<?xml version="1.0" encoding="utf-8"?>
<!--XBRL document created with Toppan Merrill Bridge  11.1.0.0 -->
<!--Based on XBRL 2.1-->
<!--Created on: 11/18/2025 9:28:30 PM-->
<!--Modified on: 11/18/2025 9:28:30 PM-->
<link:linkbase xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xbrli="http://www.xbrl.org/2003/instance">
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#StatementUnauditedCondensedConsolidatedStatementsOfStockholdersDeficitEquity" roleURI="http://www.heliusmedical.com/20220331/taxonomy/role/StatementUnauditedCondensedConsolidatedStatementsOfStockholdersDeficitEquity" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureCommonStockAndWarrantsTables" roleURI="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsTables" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureBusinessOrganizationNatureOfOperationsAndBasisOfPresentationDetails" roleURI="http://www.heliusmedical.com/role/DisclosureBusinessOrganizationNatureOfOperationsAndBasisOfPresentationDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureDigitalAssetsFairValueActivityDetails" roleURI="http://www.heliusmedical.com/role/DisclosureDigitalAssetsFairValueActivityDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureDigitalAssetsMasterLoanAgreementDetails" roleURI="http://www.heliusmedical.com/role/DisclosureDigitalAssetsMasterLoanAgreementDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureFairValueMeasurementsDigitalAssetsToFairValueMeasurementsDetails" roleURI="http://www.heliusmedical.com/role/DisclosureFairValueMeasurementsDigitalAssetsToFairValueMeasurementsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureFairValueMeasurementsDerivativeLiabilityWarrantsToFairValueMeasurementsDetails" roleURI="http://www.heliusmedical.com/role/DisclosureFairValueMeasurementsDerivativeLiabilityWarrantsToFairValueMeasurementsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureCommonStockAndWarrantsSeptember2025PrivatePlacementDetails" roleURI="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsSeptember2025PrivatePlacementDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureCommonStockAndWarrantsSeptember2025AdvisorWarrantsDetails" roleURI="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsSeptember2025AdvisorWarrantsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureCommonStockAndWarrantsJune2025OfferingDetails" roleURI="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsJune2025OfferingDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureCommonStockAndWarrantsJune2025OfferingEstimateFairValueOfWarrantsAtIssuanceDateDetails" roleURI="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsJune2025OfferingEstimateFairValueOfWarrantsAtIssuanceDateDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureCommonStockAndWarrantsApril2025PrivatePlacementDetails" roleURI="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsApril2025PrivatePlacementDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureCommonStockAndWarrants2024PublicOfferingDetails" roleURI="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrants2024PublicOfferingDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureCommonStockAndWarrantsWarrantInducementDetails" roleURI="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsWarrantInducementDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureCommonStockAndWarrants2025AtMarketOfferingDetails" roleURI="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrants2025AtMarketOfferingDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureCommonStockAndWarrants2023AtMarketOfferingDetails" roleURI="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrants2023AtMarketOfferingDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureCommonStockAndWarrantsSeptember2025WarrantsDetails" roleURI="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsSeptember2025WarrantsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureCommonStockAndWarrantsWarrantsFairValueInputsForSeptember2025WarrantsDetails" roleURI="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsWarrantsFairValueInputsForSeptember2025WarrantsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureCommonStockAndWarrantsRollForwardOfFairValueOfDerivativeLiabilitiesDetails" roleURI="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsRollForwardOfFairValueOfDerivativeLiabilitiesDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureCommonStockAndWarrantsSummaryOfRollForwardOfNumberOfSharesOfCommonStockUnderlyingWarrantsIssuedDetails" roleURI="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsSummaryOfRollForwardOfNumberOfSharesOfCommonStockUnderlyingWarrantsIssuedDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureStockBasedCompensationPlanInformationDetails" roleURI="http://www.heliusmedical.com/role/DisclosureStockBasedCompensationPlanInformationDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureStockBasedCompensationAwardsGrantedAndOutstandingDetails" roleURI="http://www.heliusmedical.com/20220331/taxonomy/role/DisclosureStockBasedCompensationAwardsGrantedAndOutstandingDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureStockBasedCompensationFairValueAssumptionsAndOtherDetails" roleURI="http://www.heliusmedical.com/20220331/taxonomy/role/DisclosureStockBasedCompensationFairValueAssumptionsAndOtherDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureStockBasedCompensationStockBasedCompensationExpenseDetails" roleURI="http://www.heliusmedical.com/20220331/taxonomy/role/DisclosureStockBasedCompensationStockBasedCompensationExpenseDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureBasicAndDilutedLossPerSharePublicOfferingDetails" roleURI="http://www.heliusmedical.com/role/DisclosureBasicAndDilutedLossPerSharePublicOfferingDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureBasicAndDilutedLossPerShareAntidilutiveSecuritiesDetails" roleURI="http://www.heliusmedical.com/role/DisclosureBasicAndDilutedLossPerShareAntidilutiveSecuritiesDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureRelatedPartiesStrategicAdvisoryAgreementTradingAdvisoryAgreementDetails" roleURI="http://www.heliusmedical.com/role/DisclosureRelatedPartiesStrategicAdvisoryAgreementTradingAdvisoryAgreementDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <roleRef xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureSubsequentEventsDetails" roleURI="http://www.heliusmedical.com/role/DisclosureSubsequentEventsDetails" xmlns="http://www.xbrl.org/2003/linkbase" />
  <link:roleRef roleURI="http://www.heliusmedical.com/role/DisclosureStandardAndCustomAxisDomainDefaults" xlink:type="simple" xlink:href="hsdt-20250930.xsd#DisclosureStandardAndCustomAxisDomainDefaults" />
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-roles-2025.xsd#eedm" />
  <link:arcroleRef arcroleURI="http://www.esma.europa.eu/xbrl/esef/arcrole/wider-narrower" xlink:type="simple" xlink:href="http://www.xbrl.org/lrr/arcrole/esma-arcrole-2018-11-21.xsd#wider-narrower" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" />
  <link:definitionLink xlink:type="extended" xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1" xlink:title="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ValuationTechniqueOptionPricingModelMember" xlink:label="us-gaap_ValuationTechniqueOptionPricingModelMember" xlink:title="us-gaap_ValuationTechniqueOptionPricingModelMember" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1" xlink:to="us-gaap_ValuationTechniqueOptionPricingModelMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1 To us-gaap_ValuationTechniqueOptionPricingModelMember" order="1" priority="0" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WarrantyRightsAndObligationsFairValueOptionMember" xlink:label="us-gaap_WarrantyRightsAndObligationsFairValueOptionMember" xlink:title="us-gaap_WarrantyRightsAndObligationsFairValueOptionMember" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1" xlink:to="us-gaap_WarrantyRightsAndObligationsFairValueOptionMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:title="definition:us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_1 To us-gaap_WarrantyRightsAndObligationsFairValueOptionMember" order="2" priority="0" />
  </link:definitionLink>
  <link:definitionLink xlink:type="extended" xlink:role="http://www.heliusmedical.com/role/DisclosureStandardAndCustomAxisDomainDefaults">
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis" xlink:label="ProductOrServiceAxis" xlink:title="ProductOrServiceAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain" xlink:label="ProductsAndServicesDomain" xlink:title="ProductsAndServicesDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ProductOrServiceAxis" xlink:to="ProductsAndServicesDomain" xlink:title="definition: ProductOrServiceAxis to ProductsAndServicesDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="StatementEquityComponentsAxis" xlink:title="StatementEquityComponentsAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain" xlink:label="EquityComponentDomain" xlink:title="EquityComponentDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementEquityComponentsAxis" xlink:to="EquityComponentDomain" xlink:title="definition: StatementEquityComponentsAxis to EquityComponentDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis" xlink:label="AwardTypeAxis" xlink:title="AwardTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AwardTypeAxis" xlink:to="ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:title="definition: AwardTypeAxis to ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="ConcentrationRiskByBenchmarkAxis" xlink:title="ConcentrationRiskByBenchmarkAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="ConcentrationRiskBenchmarkDomain" xlink:title="ConcentrationRiskBenchmarkDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ConcentrationRiskByBenchmarkAxis" xlink:to="ConcentrationRiskBenchmarkDomain" xlink:title="definition: ConcentrationRiskByBenchmarkAxis to ConcentrationRiskBenchmarkDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis" xlink:label="PropertyPlantAndEquipmentByTypeAxis" xlink:title="PropertyPlantAndEquipmentByTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain" xlink:label="PropertyPlantAndEquipmentTypeDomain" xlink:title="PropertyPlantAndEquipmentTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PropertyPlantAndEquipmentByTypeAxis" xlink:to="PropertyPlantAndEquipmentTypeDomain" xlink:title="definition: PropertyPlantAndEquipmentByTypeAxis to PropertyPlantAndEquipmentTypeDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis" xlink:label="RangeAxis" xlink:title="RangeAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="RangeMember" xlink:title="RangeMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RangeAxis" xlink:to="RangeMember" xlink:title="definition: RangeAxis to RangeMember" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="BusinessAcquisitionAxis" xlink:title="BusinessAcquisitionAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="BusinessAcquisitionAcquireeDomain" xlink:title="BusinessAcquisitionAcquireeDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="BusinessAcquisitionAxis" xlink:to="BusinessAcquisitionAcquireeDomain" xlink:title="definition: BusinessAcquisitionAxis to BusinessAcquisitionAcquireeDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="IncomeStatementLocationAxis" xlink:title="IncomeStatementLocationAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="IncomeStatementLocationDomain" xlink:title="IncomeStatementLocationDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="IncomeStatementLocationAxis" xlink:to="IncomeStatementLocationDomain" xlink:title="definition: IncomeStatementLocationAxis to IncomeStatementLocationDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="RelatedPartyTransactionsByRelatedPartyAxis" xlink:title="RelatedPartyTransactionsByRelatedPartyAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain" xlink:label="RelatedPartyDomain" xlink:title="RelatedPartyDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="RelatedPartyDomain" xlink:title="definition: RelatedPartyTransactionsByRelatedPartyAxis to RelatedPartyDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="TypeOfArrangementAxis" xlink:title="TypeOfArrangementAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="ArrangementsAndNonarrangementTransactionsMember" xlink:title="ArrangementsAndNonarrangementTransactionsMember" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TypeOfArrangementAxis" xlink:to="ArrangementsAndNonarrangementTransactionsMember" xlink:title="definition: TypeOfArrangementAxis to ArrangementsAndNonarrangementTransactionsMember" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:title="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="AntidilutiveSecuritiesNameDomain" xlink:title="AntidilutiveSecuritiesNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="AntidilutiveSecuritiesNameDomain" xlink:title="definition: AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis to AntidilutiveSecuritiesNameDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:title="FiniteLivedIntangibleAssetsByMajorClassAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="FiniteLivedIntangibleAssetsMajorClassNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:title="definition: FiniteLivedIntangibleAssetsByMajorClassAxis to FiniteLivedIntangibleAssetsMajorClassNameDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis" xlink:label="StatementClassOfStockAxis" xlink:title="StatementClassOfStockAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain" xlink:title="ClassOfStockDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="StatementClassOfStockAxis" xlink:to="ClassOfStockDomain" xlink:title="definition: StatementClassOfStockAxis to ClassOfStockDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="SubsidiarySaleOfStockAxis" xlink:title="SubsidiarySaleOfStockAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="SaleOfStockNameOfTransactionDomain" xlink:title="SaleOfStockNameOfTransactionDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="SubsidiarySaleOfStockAxis" xlink:to="SaleOfStockNameOfTransactionDomain" xlink:title="definition: SubsidiarySaleOfStockAxis to SaleOfStockNameOfTransactionDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualAxis" xlink:label="TitleOfIndividualAxis" xlink:title="TitleOfIndividualAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain" xlink:label="TitleOfIndividualWithRelationshipToEntityDomain" xlink:title="TitleOfIndividualWithRelationshipToEntityDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="TitleOfIndividualAxis" xlink:to="TitleOfIndividualWithRelationshipToEntityDomain" xlink:title="definition: TitleOfIndividualAxis to TitleOfIndividualWithRelationshipToEntityDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis" xlink:label="CounterpartyNameAxis" xlink:title="CounterpartyNameAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="RepurchaseAgreementCounterpartyNameDomain" xlink:title="RepurchaseAgreementCounterpartyNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="CounterpartyNameAxis" xlink:to="RepurchaseAgreementCounterpartyNameDomain" xlink:title="definition: CounterpartyNameAxis to RepurchaseAgreementCounterpartyNameDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="ClassOfWarrantOrRightAxis" xlink:title="ClassOfWarrantOrRightAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="ClassOfWarrantOrRightDomain" xlink:title="ClassOfWarrantOrRightDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="ClassOfWarrantOrRightAxis" xlink:to="ClassOfWarrantOrRightDomain" xlink:title="definition: ClassOfWarrantOrRightAxis to ClassOfWarrantOrRightDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis" xlink:label="PlanNameAxis" xlink:title="PlanNameAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain" xlink:label="PlanNameDomain" xlink:title="PlanNameDomain" />
    <link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="PlanNameAxis" xlink:to="PlanNameDomain" xlink:title="definition: PlanNameAxis to PlanNameDomain" use="optional" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis" xlink:label="srt_StatementGeographicalAxis_1" xlink:title="srt_StatementGeographicalAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain" xlink:label="srt_SegmentGeographicalDomain_1" xlink:title="srt_SegmentGeographicalDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="srt_StatementGeographicalAxis_1" xlink:to="srt_SegmentGeographicalDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_StatementGeographicalAxis_1 To srt_SegmentGeographicalDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis_1" xlink:title="us-gaap_SubsequentEventTypeAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain_1" xlink:title="us-gaap_SubsequentEventTypeDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_SubsequentEventTypeAxis_1" xlink:to="us-gaap_SubsequentEventTypeDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_SubsequentEventTypeAxis_1 To us-gaap_SubsequentEventTypeDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementScenarioAxis" xlink:label="srt_StatementScenarioAxis_1" xlink:title="srt_StatementScenarioAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain" xlink:label="srt_ScenarioUnspecifiedDomain_1" xlink:title="srt_ScenarioUnspecifiedDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="srt_StatementScenarioAxis_1" xlink:to="srt_ScenarioUnspecifiedDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_StatementScenarioAxis_1 To srt_ScenarioUnspecifiedDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegistrationPaymentArrangementByArrangementAxis" xlink:label="us-gaap_RegistrationPaymentArrangementByArrangementAxis" xlink:title="us-gaap_RegistrationPaymentArrangementByArrangementAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RegistrationPaymentArrangementArrangementDomain" xlink:label="us-gaap_RegistrationPaymentArrangementArrangementDomain" xlink:title="us-gaap_RegistrationPaymentArrangementArrangementDomain" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_RegistrationPaymentArrangementByArrangementAxis" xlink:to="us-gaap_RegistrationPaymentArrangementArrangementDomain" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_RegistrationPaymentArrangementByArrangementAxis To us-gaap_RegistrationPaymentArrangementArrangementDomain" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" xlink:title="us-gaap_FinancialInstrumentAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:title="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_FinancialInstrumentAxis To us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="us-gaap_MeasurementInputTypeAxis" xlink:title="us-gaap_MeasurementInputTypeAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="us-gaap_MeasurementInputTypeDomain" xlink:title="us-gaap_MeasurementInputTypeDomain" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_MeasurementInputTypeAxis" xlink:to="us-gaap_MeasurementInputTypeDomain" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_MeasurementInputTypeAxis To us-gaap_MeasurementInputTypeDomain" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByLiabilityClassAxis" xlink:label="us-gaap_FairValueByLiabilityClassAxis" xlink:title="us-gaap_FairValueByLiabilityClassAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" xlink:title="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_FairValueByLiabilityClassAxis" xlink:to="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_FairValueByLiabilityClassAxis To us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CurrencyAxis" xlink:label="srt_CurrencyAxis" xlink:title="srt_CurrencyAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/currency/2025/currency-2025.xsd#currency_AllCurrenciesDomain" xlink:label="currency_AllCurrenciesDomain" xlink:title="currency_AllCurrenciesDomain" />
    <link:definitionArc xlink:type="arc" xlink:from="srt_CurrencyAxis" xlink:to="currency_AllCurrenciesDomain" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_CurrencyAxis To currency_AllCurrenciesDomain" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:title="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:title="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_FairValueByFairValueHierarchyLevelAxis To us-gaap_FairValueMeasurementsFairValueHierarchyDomain" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:label="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:title="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfAdoptionMember" xlink:label="us-gaap_TypeOfAdoptionMember" xlink:title="us-gaap_TypeOfAdoptionMember" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_AdjustmentsForNewAccountingPronouncementsAxis" xlink:to="us-gaap_TypeOfAdoptionMember" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_AdjustmentsForNewAccountingPronouncementsAxis To us-gaap_TypeOfAdoptionMember" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis_1" xlink:title="us-gaap_DebtInstrumentAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain_1" xlink:title="us-gaap_DebtInstrumentNameDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_DebtInstrumentAxis_1" xlink:to="us-gaap_DebtInstrumentNameDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_DebtInstrumentAxis_1 To us-gaap_DebtInstrumentNameDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReportingUnitAxis" xlink:label="us-gaap_ReportingUnitAxis_1" xlink:title="us-gaap_ReportingUnitAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReportingUnitDomain" xlink:label="us-gaap_ReportingUnitDomain_1" xlink:title="us-gaap_ReportingUnitDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_ReportingUnitAxis_1" xlink:to="us-gaap_ReportingUnitDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_ReportingUnitAxis_1 To us-gaap_ReportingUnitDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablesPeriodPastDueAxis" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueAxis_1" xlink:title="us-gaap_FinancingReceivablesPeriodPastDueAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancingReceivablesPeriodPastDueDomain" xlink:label="us-gaap_FinancingReceivablesPeriodPastDueDomain_1" xlink:title="us-gaap_FinancingReceivablesPeriodPastDueDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_FinancingReceivablesPeriodPastDueAxis_1" xlink:to="us-gaap_FinancingReceivablesPeriodPastDueDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_FinancingReceivablesPeriodPastDueAxis_1 To us-gaap_FinancingReceivablesPeriodPastDueDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="us-gaap_ConcentrationRiskByTypeAxis_1" xlink:title="us-gaap_ConcentrationRiskByTypeAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="us-gaap_ConcentrationRiskTypeDomain_1" xlink:title="us-gaap_ConcentrationRiskTypeDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_ConcentrationRiskByTypeAxis_1" xlink:to="us-gaap_ConcentrationRiskTypeDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_ConcentrationRiskByTypeAxis_1 To us-gaap_ConcentrationRiskTypeDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis" xlink:label="srt_MajorCustomersAxis_1" xlink:title="srt_MajorCustomersAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain" xlink:label="srt_NameOfMajorCustomerDomain_1" xlink:title="srt_NameOfMajorCustomerDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="srt_MajorCustomersAxis_1" xlink:to="srt_NameOfMajorCustomerDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_MajorCustomersAxis_1 To srt_NameOfMajorCustomerDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ExpirationPeriodAxis" xlink:label="hsdt_ExpirationPeriodAxis_1" xlink:title="hsdt_ExpirationPeriodAxis_1" />
    <link:loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ExpirationPeriodDomain" xlink:label="hsdt_ExpirationPeriodDomain_1" xlink:title="hsdt_ExpirationPeriodDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="hsdt_ExpirationPeriodAxis_1" xlink:to="hsdt_ExpirationPeriodDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:hsdt_ExpirationPeriodAxis_1 To hsdt_ExpirationPeriodDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TaxCreditCarryforwardAxis" xlink:label="us-gaap_TaxCreditCarryforwardAxis_1" xlink:title="us-gaap_TaxCreditCarryforwardAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TaxCreditCarryforwardNameDomain" xlink:label="us-gaap_TaxCreditCarryforwardNameDomain_1" xlink:title="us-gaap_TaxCreditCarryforwardNameDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_TaxCreditCarryforwardAxis_1" xlink:to="us-gaap_TaxCreditCarryforwardNameDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_TaxCreditCarryforwardAxis_1 To us-gaap_TaxCreditCarryforwardNameDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityAxis" xlink:label="us-gaap_IncomeTaxAuthorityAxis_1" xlink:title="us-gaap_IncomeTaxAuthorityAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain" xlink:label="us-gaap_IncomeTaxAuthorityDomain_1" xlink:title="us-gaap_IncomeTaxAuthorityDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_IncomeTaxAuthorityAxis_1" xlink:to="us-gaap_IncomeTaxAuthorityDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_IncomeTaxAuthorityAxis_1 To us-gaap_IncomeTaxAuthorityDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityNameAxis" xlink:label="us-gaap_IncomeTaxAuthorityNameAxis_1" xlink:title="us-gaap_IncomeTaxAuthorityNameAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityNameDomain" xlink:label="us-gaap_IncomeTaxAuthorityNameDomain_1" xlink:title="us-gaap_IncomeTaxAuthorityNameDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_IncomeTaxAuthorityNameAxis_1" xlink:to="us-gaap_IncomeTaxAuthorityNameDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_IncomeTaxAuthorityNameAxis_1 To us-gaap_IncomeTaxAuthorityNameDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GranteeStatusAxis" xlink:label="us-gaap_GranteeStatusAxis_1" xlink:title="us-gaap_GranteeStatusAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GranteeStatusDomain" xlink:label="us-gaap_GranteeStatusDomain_1" xlink:title="us-gaap_GranteeStatusDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_GranteeStatusAxis_1" xlink:to="us-gaap_GranteeStatusDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_GranteeStatusAxis_1 To us-gaap_GranteeStatusDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="us-gaap_BalanceSheetLocationAxis_1" xlink:title="us-gaap_BalanceSheetLocationAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="us-gaap_BalanceSheetLocationDomain_1" xlink:title="us-gaap_BalanceSheetLocationDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_BalanceSheetLocationAxis_1" xlink:to="us-gaap_BalanceSheetLocationDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_BalanceSheetLocationAxis_1 To us-gaap_BalanceSheetLocationDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="us-gaap_StatementBusinessSegmentsAxis_1" xlink:title="us-gaap_StatementBusinessSegmentsAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain" xlink:label="us-gaap_SegmentDomain_1" xlink:title="us-gaap_SegmentDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_StatementBusinessSegmentsAxis_1" xlink:to="us-gaap_SegmentDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_StatementBusinessSegmentsAxis_1 To us-gaap_SegmentDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CryptoAssetAxis" xlink:label="srt_CryptoAssetAxis_1" xlink:title="srt_CryptoAssetAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CryptoAssetDomain" xlink:label="srt_CryptoAssetDomain_1" xlink:title="srt_CryptoAssetDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="srt_CryptoAssetAxis_1" xlink:to="srt_CryptoAssetDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:srt_CryptoAssetAxis_1 To srt_CryptoAssetDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis_1" xlink:title="us-gaap_FairValueByMeasurementFrequencyAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain_1" xlink:title="us-gaap_FairValueMeasurementFrequencyDomain_1" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis_1" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_FairValueByMeasurementFrequencyAxis_1 To us-gaap_FairValueMeasurementFrequencyDomain_1" order="1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="us-gaap_FairValueByMeasurementBasisAxis_1" xlink:title="us-gaap_FairValueByMeasurementBasisAxis_1" />
    <link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember_1" xlink:title="us-gaap_PortionAtFairValueFairValueDisclosureMember_1" />
    <link:definitionArc xlink:type="arc" xlink:from="us-gaap_FairValueByMeasurementBasisAxis_1" xlink:to="us-gaap_PortionAtFairValueFairValueDisclosureMember_1" use="optional" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:title="definition:us-gaap_FairValueByMeasurementBasisAxis_1 To us-gaap_PortionAtFairValueFairValueDisclosureMember_1" order="1" />
  </link:definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/20220331/taxonomy/role/StatementUnauditedCondensedConsolidatedStatementsOfStockholdersDeficitEquity" xlink:type="extended" xlink:title="995200300 - Statement - Unaudited Condensed Consolidated Statements of Stockholders' (Deficit) Equity" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable" xlink:label="us-gaap_StatementTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_StatementTable" xlink:to="us-gaap_StatementEquityComponentsAxis" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember" xlink:label="us-gaap_AdditionalPaidInCapitalMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AdditionalPaidInCapitalMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember" xlink:label="us-gaap_RetainedEarningsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_RetainedEarningsMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems" xlink:label="us-gaap_StatementLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StatementTable" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesIssued" xlink:label="us-gaap_SharesIssued" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_SharesIssued" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity" xlink:label="us-gaap_StockholdersEquity" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockholdersEquity" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodValueNewIssues" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodValueNewIssues" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalWarrantIssued" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_SharesIssuedDuringPeriodSharesSharesAndWarrants" xlink:label="hsdt_SharesIssuedDuringPeriodSharesSharesAndWarrants" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_StatementLineItems" xlink:to="hsdt_SharesIssuedDuringPeriodSharesSharesAndWarrants" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_SharesIssuedDuringPeriodValueSharesAndWarrants" xlink:label="hsdt_SharesIssuedDuringPeriodValueSharesAndWarrants" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_StatementLineItems" xlink:to="hsdt_SharesIssuedDuringPeriodValueSharesAndWarrants" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalStockIssuedIssuanceCosts" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_StockIssuedDuringPeriodSharesWarrantExercised" xlink:label="hsdt_StockIssuedDuringPeriodSharesWarrantExercised" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_StatementLineItems" xlink:to="hsdt_StockIssuedDuringPeriodSharesWarrantExercised" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_StockIssuedDuringPeriodValueWarrantExercised" xlink:label="hsdt_StockIssuedDuringPeriodValueWarrantExercised" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_StatementLineItems" xlink:to="hsdt_StockIssuedDuringPeriodValueWarrantExercised" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" xlink:label="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardGross" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" xlink:label="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss" xlink:label="us-gaap_NetIncomeLoss" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="us-gaap_StatementLineItems" xlink:to="us-gaap_NetIncomeLoss" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsTables" xlink:type="extended" xlink:title="99930603 - Disclosure - COMMON STOCK AND WARRANTS (Tables)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityTable" xlink:label="hsdt_ScheduleOfStockholdersEquityTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_ClassOfWarrantOrRightAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_WarrantsIssuedJune62025Member" xlink:label="hsdt_WarrantsIssuedJune62025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_WarrantsIssuedJune62025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_StapledWarrants2025Member" xlink:label="hsdt_StapledWarrants2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_StapledWarrants2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityLineItems" xlink:label="hsdt_ScheduleOfStockholdersEquityLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ScheduleOfStockholdersEquityTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTableTextBlock" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock" xlink:label="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTextBlock" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfStockholdersEquityNoteWarrantsOrRightsTextBlock" xlink:label="us-gaap_ScheduleOfStockholdersEquityNoteWarrantsOrRightsTextBlock" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ScheduleOfStockholdersEquityNoteWarrantsOrRightsTextBlock" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureBusinessOrganizationNatureOfOperationsAndBasisOfPresentationDetails" xlink:type="extended" xlink:title="99940101 - Disclosure - BUSINESS ORGANIZATION, NATURE OF OPERATIONS AND BASIS OF PRESENTATION (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfBasisOfPresentationTable" xlink:label="hsdt_ScheduleOfBasisOfPresentationTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="hsdt_ScheduleOfBasisOfPresentationTable" xlink:to="srt_RangeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="srt_RangeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_BasisOfPresentationLineItems" xlink:label="hsdt_BasisOfPresentationLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="hsdt_BasisOfPresentationLineItems" xlink:to="hsdt_ScheduleOfBasisOfPresentationTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_NumberOfProcessingTransactionsPerSecond" xlink:label="hsdt_NumberOfProcessingTransactionsPerSecond" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_BasisOfPresentationLineItems" xlink:to="hsdt_NumberOfProcessingTransactionsPerSecond" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_NumberOfBlockchainDevelopersOnBoarded" xlink:label="hsdt_NumberOfBlockchainDevelopersOnBoarded" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="hsdt_BasisOfPresentationLineItems" xlink:to="hsdt_NumberOfBlockchainDevelopersOnBoarded" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="hsdt_BasisOfPresentationLineItems" xlink:to="us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="hsdt_BasisOfPresentationLineItems" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_WorkingCapital" xlink:label="hsdt_WorkingCapital" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="hsdt_BasisOfPresentationLineItems" xlink:to="hsdt_WorkingCapital" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivities" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="hsdt_BasisOfPresentationLineItems" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivities" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureDigitalAssetsFairValueActivityDetails" xlink:type="extended" xlink:title="99940302 - Disclosure - DIGITAL ASSETS - Fair value activity (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CryptoAssetActivityTable" xlink:label="us-gaap_CryptoAssetActivityTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CryptoAssetAxis" xlink:label="srt_CryptoAssetAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_CryptoAssetActivityTable" xlink:to="srt_CryptoAssetAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CryptoAssetDomain" xlink:label="srt_CryptoAssetDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CryptoAssetAxis" xlink:to="srt_CryptoAssetDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CryptoAssetsTokensUnrestrictedMember" xlink:label="hsdt_CryptoAssetsTokensUnrestrictedMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_CryptoAssetDomain" xlink:to="hsdt_CryptoAssetsTokensUnrestrictedMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CryptoAssetsTokensRestrictedMember" xlink:label="hsdt_CryptoAssetsTokensRestrictedMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_CryptoAssetDomain" xlink:to="hsdt_CryptoAssetsTokensRestrictedMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CryptoAssetActivityLineItems" xlink:label="us-gaap_CryptoAssetActivityLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_CryptoAssetActivityLineItems" xlink:to="us-gaap_CryptoAssetActivityTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CryptoAssetRollForward" xlink:label="us-gaap_CryptoAssetRollForward" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_CryptoAssetActivityLineItems" xlink:to="us-gaap_CryptoAssetRollForward" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CryptoAssetFairValue" xlink:label="us-gaap_CryptoAssetFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_CryptoAssetRollForward" xlink:to="us-gaap_CryptoAssetFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CryptoAssetCustomerReceipt" xlink:label="us-gaap_CryptoAssetCustomerReceipt" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_CryptoAssetRollForward" xlink:to="us-gaap_CryptoAssetCustomerReceipt" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CryptoAssetPurchase" xlink:label="us-gaap_CryptoAssetPurchase" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_CryptoAssetRollForward" xlink:to="us-gaap_CryptoAssetPurchase" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_StakingRewardsIncome" xlink:label="hsdt_StakingRewardsIncome" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_CryptoAssetRollForward" xlink:to="hsdt_StakingRewardsIncome" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CryptoAssetUnrealizedGainLossOperating" xlink:label="us-gaap_CryptoAssetUnrealizedGainLossOperating" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_CryptoAssetRollForward" xlink:to="us-gaap_CryptoAssetUnrealizedGainLossOperating" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureDigitalAssetsMasterLoanAgreementDetails" xlink:type="extended" xlink:title="99940303 - Disclosure - DIGITAL ASSETS - Master Loan Agreement (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShortTermDebtTable" xlink:label="us-gaap_ScheduleOfShortTermDebtTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfShortTermDebtTable" xlink:to="us-gaap_DebtInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_MasterLoanAgreementMember" xlink:label="hsdt_MasterLoanAgreementMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="hsdt_MasterLoanAgreementMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermDebtLineItems" xlink:label="us-gaap_ShortTermDebtLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ShortTermDebtLineItems" xlink:to="us-gaap_ScheduleOfShortTermDebtTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_DebtInstrumentMinimumCollateralRatio" xlink:label="hsdt_DebtInstrumentMinimumCollateralRatio" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShortTermDebtLineItems" xlink:to="hsdt_DebtInstrumentMinimumCollateralRatio" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermBorrowings" xlink:label="us-gaap_ShortTermBorrowings" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShortTermDebtLineItems" xlink:to="us-gaap_ShortTermBorrowings" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureFairValueMeasurementsDigitalAssetsToFairValueMeasurementsDetails" xlink:type="extended" xlink:title="99940501 - Disclosure - FAIR VALUE MEASUREMENTS - Digital assets to fair value measurements (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="us-gaap_FairValueMeasurementsRecurringMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="us-gaap_FairValueInputsLevel1Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel1Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="us-gaap_FairValueByMeasurementBasisAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByMeasurementBasisAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementBasisAxis" xlink:to="us-gaap_PortionAtFairValueFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="us-gaap_EstimateOfFairValueFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_EstimateOfFairValueFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="srt_RangeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="srt_RangeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_WeightedAverageMember" xlink:label="srt_WeightedAverageMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="srt_RangeMember" xlink:to="srt_WeightedAverageMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CryptoAssetFairValueUnrestricted" xlink:label="us-gaap_CryptoAssetFairValueUnrestricted" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_CryptoAssetFairValueUnrestricted" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CryptoAssetFairValueRestricted" xlink:label="us-gaap_CryptoAssetFairValueRestricted" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_CryptoAssetFairValueRestricted" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CryptoAssetFairValue" xlink:label="us-gaap_CryptoAssetFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_CryptoAssetFairValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CryptoAssetFairValuePerUnit" xlink:label="hsdt_CryptoAssetFairValuePerUnit" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="hsdt_CryptoAssetFairValuePerUnit" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_AverageRateOfDiscountForLackOfMarketability" xlink:label="hsdt_AverageRateOfDiscountForLackOfMarketability" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="hsdt_AverageRateOfDiscountForLackOfMarketability" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureFairValueMeasurementsDerivativeLiabilityWarrantsToFairValueMeasurementsDetails" xlink:type="extended" xlink:title="99940502 - Disclosure - FAIR VALUE MEASUREMENTS - Derivative liability warrants to fair value measurements (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementFrequencyAxis" xlink:label="us-gaap_FairValueByMeasurementFrequencyAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByMeasurementFrequencyAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementFrequencyDomain" xlink:label="us-gaap_FairValueMeasurementFrequencyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementFrequencyAxis" xlink:to="us-gaap_FairValueMeasurementFrequencyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsRecurringMember" xlink:label="us-gaap_FairValueMeasurementsRecurringMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementFrequencyDomain" xlink:to="us-gaap_FairValueMeasurementsRecurringMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="us-gaap_FairValueByFairValueHierarchyLevelAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByFairValueHierarchyLevelAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:to="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="us-gaap_FairValueInputsLevel3Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:to="us-gaap_FairValueInputsLevel3Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementBasisAxis" xlink:label="us-gaap_FairValueByMeasurementBasisAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FairValueByMeasurementBasisAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:label="us-gaap_PortionAtFairValueFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FairValueByMeasurementBasisAxis" xlink:to="us-gaap_PortionAtFairValueFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember" xlink:label="us-gaap_EstimateOfFairValueFairValueDisclosureMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PortionAtFairValueFairValueDisclosureMember" xlink:to="us-gaap_EstimateOfFairValueFairValueDisclosureMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_StapledWarrants2025Member" xlink:label="hsdt_StapledWarrants2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="hsdt_StapledWarrants2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilities" xlink:label="us-gaap_DerivativeLiabilities" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:to="us-gaap_DerivativeLiabilities" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsSeptember2025PrivatePlacementDetails" xlink:type="extended" xlink:title="99940601 - Disclosure - COMMON STOCK AND WARRANTS - September 2025 Private Placement (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityTable" xlink:label="hsdt_ScheduleOfStockholdersEquityTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_Pipe2025OfferingsMember" xlink:label="hsdt_Pipe2025OfferingsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="hsdt_Pipe2025OfferingsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_September2025PrivatePlacementCryptocurrencyOfferingMember" xlink:label="hsdt_September2025PrivatePlacementCryptocurrencyOfferingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="hsdt_Pipe2025OfferingsMember" xlink:to="hsdt_September2025PrivatePlacementCryptocurrencyOfferingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_September2025PrivatePlacementCashOfferingMember" xlink:label="hsdt_September2025PrivatePlacementCashOfferingMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_Pipe2025OfferingsMember" xlink:to="hsdt_September2025PrivatePlacementCashOfferingMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_ClassOfWarrantOrRightAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PreFundedWarrants2025Member" xlink:label="hsdt_PreFundedWarrants2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_PreFundedWarrants2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_StapledWarrants2025Member" xlink:label="hsdt_StapledWarrants2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_StapledWarrants2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="srt_CounterpartyNameAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ClearStreetLlcMember" xlink:label="hsdt_ClearStreetLlcMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="hsdt_ClearStreetLlcMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityLineItems" xlink:label="hsdt_ScheduleOfStockholdersEquityLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ScheduleOfStockholdersEquityTable" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="us-gaap_SharesIssuedPricePerShare" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_SharesIssuedPricePerShare" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ClassOfWarrantOrRightExercisePriceDiscountFromSharePrice" xlink:label="hsdt_ClassOfWarrantOrRightExercisePriceDiscountFromSharePrice" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ClassOfWarrantOrRightExercisePriceDiscountFromSharePrice" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PlacementAgentCompensationAmount" xlink:label="hsdt_PlacementAgentCompensationAmount" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_PlacementAgentCompensationAmount" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_NonCashFinancingCosts" xlink:label="hsdt_NonCashFinancingCosts" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_NonCashFinancingCosts" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PlacementAgentMaximumReimbursementOfLegalFees" xlink:label="hsdt_PlacementAgentMaximumReimbursementOfLegalFees" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_PlacementAgentMaximumReimbursementOfLegalFees" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOrSaleOfEquity" xlink:label="us-gaap_ProceedsFromIssuanceOrSaleOfEquity" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ProceedsFromIssuanceOrSaleOfEquity" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ProceedsOfDigitalAssetsFromIssuanceOrSaleOfEquity" xlink:label="hsdt_ProceedsOfDigitalAssetsFromIssuanceOrSaleOfEquity" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ProceedsOfDigitalAssetsFromIssuanceOrSaleOfEquity" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CryptoAssetsReceivedInKindFromPrivatePlacement" xlink:label="hsdt_CryptoAssetsReceivedInKindFromPrivatePlacement" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_CryptoAssetsReceivedInKindFromPrivatePlacement" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CryptoAssetsReceivedInKindUsdc" xlink:label="hsdt_CryptoAssetsReceivedInKindUsdc" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_CryptoAssetsReceivedInKindUsdc" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CryptoAssetsReceivedInKindUsdt" xlink:label="hsdt_CryptoAssetsReceivedInKindUsdt" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_CryptoAssetsReceivedInKindUsdt" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsOfStockIssuanceCosts" xlink:label="us-gaap_PaymentsOfStockIssuanceCosts" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_PaymentsOfStockIssuanceCosts" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="us-gaap_SaleOfStockConsiderationReceivedOnTransaction" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_SaleOfStockConsiderationReceivedOnTransaction" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsSeptember2025AdvisorWarrantsDetails" xlink:type="extended" xlink:title="99940602 - Disclosure - COMMON STOCK AND WARRANTS - September 2025 Advisor Warrants (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityTable" xlink:label="hsdt_ScheduleOfStockholdersEquityTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_ClassOfWarrantOrRightAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_September2025AdvisorWarrantsMember" xlink:label="hsdt_September2025AdvisorWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_September2025AdvisorWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PanteraBaseAdvisorWarrantsMember" xlink:label="hsdt_PanteraBaseAdvisorWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="hsdt_September2025AdvisorWarrantsMember" xlink:to="hsdt_PanteraBaseAdvisorWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_SummerBaseAdvisorWarrantsMember" xlink:label="hsdt_SummerBaseAdvisorWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_September2025AdvisorWarrantsMember" xlink:to="hsdt_SummerBaseAdvisorWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityLineItems" xlink:label="hsdt_ScheduleOfStockholdersEquityLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ScheduleOfStockholdersEquityTable" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PercentageOfAdditionalWarrantsGrantedBasedOnSharesIssuedUponExercise" xlink:label="hsdt_PercentageOfAdditionalWarrantsGrantedBasedOnSharesIssuedUponExercise" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_PercentageOfAdditionalWarrantsGrantedBasedOnSharesIssuedUponExercise" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_NonCashFinancingCosts" xlink:label="hsdt_NonCashFinancingCosts" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_NonCashFinancingCosts" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="us-gaap_SharesIssuedPricePerShare" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_SharesIssuedPricePerShare" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_AdvisorLockUpPeriod" xlink:label="hsdt_AdvisorLockUpPeriod" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_AdvisorLockUpPeriod" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsJune2025OfferingDetails" xlink:type="extended" xlink:title="99940603 - Disclosure - COMMON STOCK AND WARRANTS - June 2025 Offering (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityTable" xlink:label="hsdt_ScheduleOfStockholdersEquityTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PublicOffering2025Member" xlink:label="hsdt_PublicOffering2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="hsdt_PublicOffering2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_ClassOfWarrantOrRightAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PreFundedWarrants2025Member" xlink:label="hsdt_PreFundedWarrants2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_PreFundedWarrants2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CommonStockWarrantsMember" xlink:label="hsdt_CommonStockWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_CommonStockWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PlacementAgentWarrantsMember" xlink:label="hsdt_PlacementAgentWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_PlacementAgentWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementScenarioAxis" xlink:label="srt_StatementScenarioAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="srt_StatementScenarioAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain" xlink:label="srt_ScenarioUnspecifiedDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_StatementScenarioAxis" xlink:to="srt_ScenarioUnspecifiedDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_FirstResetDateMember" xlink:label="hsdt_FirstResetDateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_ScenarioUnspecifiedDomain" xlink:to="hsdt_FirstResetDateMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_SecondResetDateMember" xlink:label="hsdt_SecondResetDateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_ScenarioUnspecifiedDomain" xlink:to="hsdt_SecondResetDateMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="srt_CounterpartyNameAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_MaximGroupLlcMember" xlink:label="hsdt_MaximGroupLlcMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="hsdt_MaximGroupLlcMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityLineItems" xlink:label="hsdt_ScheduleOfStockholdersEquityLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ScheduleOfStockholdersEquityTable" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_SaleOfStockCombinedOfferingPricePerShare" xlink:label="hsdt_SaleOfStockCombinedOfferingPricePerShare" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_SaleOfStockCombinedOfferingPricePerShare" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ClassOfWarrantOrRightExercised" xlink:label="hsdt_ClassOfWarrantOrRightExercised" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ClassOfWarrantOrRightExercised" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ClassOfWarrantOrRightIssuePriceOfWarrantsOrRights" xlink:label="hsdt_ClassOfWarrantOrRightIssuePriceOfWarrantsOrRights" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ClassOfWarrantOrRightIssuePriceOfWarrantsOrRights" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WarrantsAndRightsOutstandingTerm" xlink:label="us-gaap_WarrantsAndRightsOutstandingTerm" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_WarrantsAndRightsOutstandingTerm" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ShareMultiplierOnWarrantExercise" xlink:label="hsdt_ShareMultiplierOnWarrantExercise" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ShareMultiplierOnWarrantExercise" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_IncreaseInSharesAvailableForIssuance" xlink:label="hsdt_IncreaseInSharesAvailableForIssuance" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_IncreaseInSharesAvailableForIssuance" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightOutstanding" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightOutstanding" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilitiesNoncurrent" xlink:label="us-gaap_DerivativeLiabilitiesNoncurrent" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="12" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_DerivativeLiabilitiesNoncurrent" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_OfferingCostsAllocatedToDerivativeLiability" xlink:label="hsdt_OfferingCostsAllocatedToDerivativeLiability" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="13" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_OfferingCostsAllocatedToDerivativeLiability" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_DerivativeGainLossOnDerivativeNetCashFlowImpact" xlink:label="hsdt_DerivativeGainLossOnDerivativeNetCashFlowImpact" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="14" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_DerivativeGainLossOnDerivativeNetCashFlowImpact" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PlacementAgentFeesPercentageOfGrossProceedsOfOffering" xlink:label="hsdt_PlacementAgentFeesPercentageOfGrossProceedsOfOffering" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="15" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_PlacementAgentFeesPercentageOfGrossProceedsOfOffering" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PlacementAgentMaximumReimbursementOfLegalFees" xlink:label="hsdt_PlacementAgentMaximumReimbursementOfLegalFees" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="16" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_PlacementAgentMaximumReimbursementOfLegalFees" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_FinancialAdvisoryFees" xlink:label="hsdt_FinancialAdvisoryFees" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="17" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_FinancialAdvisoryFees" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOrSaleOfEquity" xlink:label="us-gaap_ProceedsFromIssuanceOrSaleOfEquity" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="18" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ProceedsFromIssuanceOrSaleOfEquity" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsOfStockIssuanceCosts" xlink:label="us-gaap_PaymentsOfStockIssuanceCosts" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="19" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_PaymentsOfStockIssuanceCosts" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RepaymentsOfDebt" xlink:label="us-gaap_RepaymentsOfDebt" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="20" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_RepaymentsOfDebt" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsJune2025OfferingEstimateFairValueOfWarrantsAtIssuanceDateDetails" xlink:type="extended" xlink:title="99940604 - Disclosure - COMMON STOCK AND WARRANTS - June 2025 Offering, Estimate the fair value of the warrants at the Issuance Date (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityTable" xlink:label="hsdt_ScheduleOfStockholdersEquityTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="us-gaap_MeasurementInputTypeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_MeasurementInputTypeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="us-gaap_MeasurementInputTypeDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_MeasurementInputTypeAxis" xlink:to="us-gaap_MeasurementInputTypeDomain" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputSharePriceMember" xlink:label="us-gaap_MeasurementInputSharePriceMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputSharePriceMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputExpectedTermMember" xlink:label="us-gaap_MeasurementInputExpectedTermMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputExpectedTermMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputPriceVolatilityMember" xlink:label="us-gaap_MeasurementInputPriceVolatilityMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputPriceVolatilityMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember" xlink:label="us-gaap_MeasurementInputRiskFreeInterestRateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputRiskFreeInterestRateMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputExpectedDividendRateMember" xlink:label="us-gaap_MeasurementInputExpectedDividendRateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputExpectedDividendRateMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CommonStockWarrantsMember" xlink:label="hsdt_CommonStockWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="hsdt_CommonStockWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_WarrantsIssuedJune62025Member" xlink:label="hsdt_WarrantsIssuedJune62025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="hsdt_CommonStockWarrantsMember" xlink:to="hsdt_WarrantsIssuedJune62025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_WarrantsIssuedJune92025Member" xlink:label="hsdt_WarrantsIssuedJune92025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_CommonStockWarrantsMember" xlink:to="hsdt_WarrantsIssuedJune92025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_WarrantsIssuedJune112025PreResetMember" xlink:label="hsdt_WarrantsIssuedJune112025PreResetMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="hsdt_CommonStockWarrantsMember" xlink:to="hsdt_WarrantsIssuedJune112025PreResetMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_WarrantsIssuedJune112025PostResetMember" xlink:label="hsdt_WarrantsIssuedJune112025PostResetMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="hsdt_CommonStockWarrantsMember" xlink:to="hsdt_WarrantsIssuedJune112025PostResetMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_WarrantsIssuedJune122025Member" xlink:label="hsdt_WarrantsIssuedJune122025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="hsdt_CommonStockWarrantsMember" xlink:to="hsdt_WarrantsIssuedJune122025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_WarrantsIssuedJune132025Member" xlink:label="hsdt_WarrantsIssuedJune132025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="hsdt_CommonStockWarrantsMember" xlink:to="hsdt_WarrantsIssuedJune132025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_WarrantsIssuedJune162025PreResetMember" xlink:label="hsdt_WarrantsIssuedJune162025PreResetMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="hsdt_CommonStockWarrantsMember" xlink:to="hsdt_WarrantsIssuedJune162025PreResetMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_WarrantsIssuedJune162025PostResetMember" xlink:label="hsdt_WarrantsIssuedJune162025PostResetMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="hsdt_CommonStockWarrantsMember" xlink:to="hsdt_WarrantsIssuedJune162025PostResetMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_WarrantsIssuedJune172025Member" xlink:label="hsdt_WarrantsIssuedJune172025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="hsdt_CommonStockWarrantsMember" xlink:to="hsdt_WarrantsIssuedJune172025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_WarrantsIssuedJune182025Member" xlink:label="hsdt_WarrantsIssuedJune182025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="hsdt_CommonStockWarrantsMember" xlink:to="hsdt_WarrantsIssuedJune182025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_WarrantsIssuedJune202025Member" xlink:label="hsdt_WarrantsIssuedJune202025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="hsdt_CommonStockWarrantsMember" xlink:to="hsdt_WarrantsIssuedJune202025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityLineItems" xlink:label="hsdt_ScheduleOfStockholdersEquityLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ScheduleOfStockholdersEquityTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilityMeasurementInput" xlink:label="us-gaap_DerivativeLiabilityMeasurementInput" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_DerivativeLiabilityMeasurementInput" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsApril2025PrivatePlacementDetails" xlink:type="extended" xlink:title="99940605 - Disclosure - COMMON STOCK AND WARRANTS - April 2025 Private Placement (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityTable" xlink:label="hsdt_ScheduleOfStockholdersEquityTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PrivatePlacement2025Member" xlink:label="hsdt_PrivatePlacement2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="hsdt_PrivatePlacement2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="srt_CounterpartyNameAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_MaximGroupLlcMember" xlink:label="hsdt_MaximGroupLlcMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="hsdt_MaximGroupLlcMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_DebtInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PromissoryNotesApril2025Member" xlink:label="hsdt_PromissoryNotesApril2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="hsdt_PromissoryNotesApril2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityLineItems" xlink:label="hsdt_ScheduleOfStockholdersEquityLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ScheduleOfStockholdersEquityTable" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PromissoryNotesOriginalIssueDiscount" xlink:label="hsdt_PromissoryNotesOriginalIssueDiscount" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_PromissoryNotesOriginalIssueDiscount" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentFaceAmount" xlink:label="us-gaap_DebtInstrumentFaceAmount" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_DebtInstrumentFaceAmount" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PlacementAgentFeesPercentageOfGrossProceedsOfOffering" xlink:label="hsdt_PlacementAgentFeesPercentageOfGrossProceedsOfOffering" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_PlacementAgentFeesPercentageOfGrossProceedsOfOffering" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PlacementAgentMaximumReimbursementOfLegalFees" xlink:label="hsdt_PlacementAgentMaximumReimbursementOfLegalFees" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_PlacementAgentMaximumReimbursementOfLegalFees" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOfDebt" xlink:label="us-gaap_ProceedsFromIssuanceOfDebt" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ProceedsFromIssuanceOfDebt" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsOfDebtIssuanceCosts" xlink:label="us-gaap_PaymentsOfDebtIssuanceCosts" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_PaymentsOfDebtIssuanceCosts" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrants2024PublicOfferingDetails" xlink:type="extended" xlink:title="99940606 - Disclosure - COMMON STOCK AND WARRANTS - 2024 Public Offering (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityTable" xlink:label="hsdt_ScheduleOfStockholdersEquityTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PublicOffering2024Member" xlink:label="hsdt_PublicOffering2024Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="hsdt_PublicOffering2024Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_StatementEquityComponentsAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_ClassOfWarrantOrRightAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PublicWarrantsMember" xlink:label="hsdt_PublicWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_PublicWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_SeriesWarrantsMember" xlink:label="hsdt_SeriesWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_SeriesWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_SeriesBWarrantsMember" xlink:label="hsdt_SeriesBWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_SeriesBWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PreFundedWarrantsMember" xlink:label="hsdt_PreFundedWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_PreFundedWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityLineItems" xlink:label="hsdt_ScheduleOfStockholdersEquityLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ScheduleOfStockholdersEquityTable" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_SaleOfStockCombinedOfferingPricePerShare" xlink:label="hsdt_SaleOfStockCombinedOfferingPricePerShare" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_SaleOfStockCombinedOfferingPricePerShare" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_SaleOfStockPreFundedWarrantsAndAccompanyingPublicWarrantsPricePerShare" xlink:label="hsdt_SaleOfStockPreFundedWarrantsAndAccompanyingPublicWarrantsPricePerShare" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_SaleOfStockPreFundedWarrantsAndAccompanyingPublicWarrantsPricePerShare" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ClassOfWarrantOrRightExercised" xlink:label="hsdt_ClassOfWarrantOrRightExercised" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ClassOfWarrantOrRightExercised" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ProceedsFromIssuanceOfCommonStockNet" xlink:label="hsdt_ProceedsFromIssuanceOfCommonStockNet" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ProceedsFromIssuanceOfCommonStockNet" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ClassOfWarrantsOrRightExpirationPeriod" xlink:label="hsdt_ClassOfWarrantsOrRightExpirationPeriod" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ClassOfWarrantsOrRightExpirationPeriod" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsWarrantInducementDetails" xlink:type="extended" xlink:title="99940607 - Disclosure - COMMON STOCK AND WARRANTS - Warrant inducement (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityTable" xlink:label="hsdt_ScheduleOfStockholdersEquityTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_ClassOfWarrantOrRightAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ExistingWarrantsMember" xlink:label="hsdt_ExistingWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_ExistingWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_InducementWarrantsMember" xlink:label="hsdt_InducementWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_InducementWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityLineItems" xlink:label="hsdt_ScheduleOfStockholdersEquityLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ScheduleOfStockholdersEquityTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromWarrantExercises" xlink:label="us-gaap_ProceedsFromWarrantExercises" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ProceedsFromWarrantExercises" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProfessionalFees" xlink:label="us-gaap_ProfessionalFees" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ProfessionalFees" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_OtherLegalAndRegulatoryExpenses" xlink:label="hsdt_OtherLegalAndRegulatoryExpenses" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_OtherLegalAndRegulatoryExpenses" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ProceedsFromWarrantExercisesNetOfExpenses" xlink:label="hsdt_ProceedsFromWarrantExercisesNetOfExpenses" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ProceedsFromWarrantExercisesNetOfExpenses" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_StockIssuedStockIssuanceCosts" xlink:label="hsdt_StockIssuedStockIssuanceCosts" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_StockIssuedStockIssuanceCosts" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" xlink:label="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_CommonStockCapitalSharesReservedForFutureIssuance" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrants2025AtMarketOfferingDetails" xlink:type="extended" xlink:title="99940608 - Disclosure - COMMON STOCK AND WARRANTS - 2025 At-The-Market Offering (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityTable" xlink:label="hsdt_ScheduleOfStockholdersEquityTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_AtMarketOffering2025Member" xlink:label="hsdt_AtMarketOffering2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="hsdt_AtMarketOffering2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityLineItems" xlink:label="hsdt_ScheduleOfStockholdersEquityLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ScheduleOfStockholdersEquityTable" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_MaximumAggregateOfferingAmount" xlink:label="hsdt_MaximumAggregateOfferingAmount" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_MaximumAggregateOfferingAmount" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_MaximumCommissionRateAsPercentageOfGrossProceeds" xlink:label="hsdt_MaximumCommissionRateAsPercentageOfGrossProceeds" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_MaximumCommissionRateAsPercentageOfGrossProceeds" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="us-gaap_SaleOfStockConsiderationReceivedOnTransaction" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_SaleOfStockConsiderationReceivedOnTransaction" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrants2023AtMarketOfferingDetails" xlink:type="extended" xlink:title="99940609 - Disclosure - COMMON STOCK AND WARRANTS - 2023 At-The-Market Offering (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityTable" xlink:label="hsdt_ScheduleOfStockholdersEquityTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_AtMarketOffering2023Member" xlink:label="hsdt_AtMarketOffering2023Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="hsdt_AtMarketOffering2023Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityLineItems" xlink:label="hsdt_ScheduleOfStockholdersEquityLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ScheduleOfStockholdersEquityTable" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_MaximumAggregateOfferingAmount" xlink:label="hsdt_MaximumAggregateOfferingAmount" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_MaximumAggregateOfferingAmount" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_MaximumCommissionRateAsPercentageOfGrossProceeds" xlink:label="hsdt_MaximumCommissionRateAsPercentageOfGrossProceeds" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_MaximumCommissionRateAsPercentageOfGrossProceeds" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ProceedsFromIssuanceOfCommonStockNet" xlink:label="hsdt_ProceedsFromIssuanceOfCommonStockNet" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ProceedsFromIssuanceOfCommonStockNet" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesIssuedPricePerShare" xlink:label="us-gaap_SharesIssuedPricePerShare" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_SharesIssuedPricePerShare" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="us-gaap_SaleOfStockConsiderationReceivedOnTransaction" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_SaleOfStockConsiderationReceivedOnTransaction" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsSeptember2025WarrantsDetails" xlink:type="extended" xlink:title="99940610 - Disclosure - COMMON STOCK AND WARRANTS - September 2025 Warrants (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityTable" xlink:label="hsdt_ScheduleOfStockholdersEquityTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_Pipe2025OfferingsMember" xlink:label="hsdt_Pipe2025OfferingsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="hsdt_Pipe2025OfferingsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis" xlink:label="us-gaap_FinancialInstrumentAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_FinancialInstrumentAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:label="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_FinancialInstrumentAxis" xlink:to="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_StapledWarrants2025Member" xlink:label="hsdt_StapledWarrants2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain" xlink:to="hsdt_StapledWarrants2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="us-gaap_MeasurementInputTypeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_MeasurementInputTypeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="us-gaap_MeasurementInputTypeDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_MeasurementInputTypeAxis" xlink:to="us-gaap_MeasurementInputTypeDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputSharePriceMember" xlink:label="us-gaap_MeasurementInputSharePriceMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputSharePriceMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_MeasurementInputSoftCallThresholdMember" xlink:label="hsdt_MeasurementInputSoftCallThresholdMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="hsdt_MeasurementInputSoftCallThresholdMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputExpectedTermMember" xlink:label="us-gaap_MeasurementInputExpectedTermMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputExpectedTermMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputPriceVolatilityMember" xlink:label="us-gaap_MeasurementInputPriceVolatilityMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputPriceVolatilityMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember" xlink:label="us-gaap_MeasurementInputRiskFreeInterestRateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputRiskFreeInterestRateMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputExpectedDividendRateMember" xlink:label="us-gaap_MeasurementInputExpectedDividendRateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputExpectedDividendRateMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_ClassOfWarrantOrRightAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightDomain" use="optional" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_StapledWarrants2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityLineItems" xlink:label="hsdt_ScheduleOfStockholdersEquityLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ScheduleOfStockholdersEquityTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilityMeasurementInput" xlink:label="us-gaap_DerivativeLiabilityMeasurementInput" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_DerivativeLiabilityMeasurementInput" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilities" xlink:label="us-gaap_DerivativeLiabilities" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_DerivativeLiabilities" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsWarrantsFairValueInputsForSeptember2025WarrantsDetails" xlink:type="extended" xlink:title="99940611 - Disclosure - COMMON STOCK AND WARRANTS - Warrants, Fair Value Inputs for September 2025 Warrants (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeAxis" xlink:label="us-gaap_MeasurementInputTypeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" xlink:to="us-gaap_MeasurementInputTypeAxis" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain" xlink:label="us-gaap_MeasurementInputTypeDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_MeasurementInputTypeAxis" xlink:to="us-gaap_MeasurementInputTypeDomain" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputExpectedTermMember" xlink:label="us-gaap_MeasurementInputExpectedTermMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputExpectedTermMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputSharePriceMember" xlink:label="us-gaap_MeasurementInputSharePriceMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputSharePriceMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputPriceVolatilityMember" xlink:label="us-gaap_MeasurementInputPriceVolatilityMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputPriceVolatilityMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputRiskFreeInterestRateMember" xlink:label="us-gaap_MeasurementInputRiskFreeInterestRateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputRiskFreeInterestRateMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputExpectedDividendRateMember" xlink:label="us-gaap_MeasurementInputExpectedDividendRateMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_MeasurementInputTypeDomain" xlink:to="us-gaap_MeasurementInputExpectedDividendRateMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:label="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilityMeasurementInput" xlink:label="us-gaap_DerivativeLiabilityMeasurementInput" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems" xlink:to="us-gaap_DerivativeLiabilityMeasurementInput" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsRollForwardOfFairValueOfDerivativeLiabilitiesDetails" xlink:type="extended" xlink:title="99940612 - Disclosure - COMMON STOCK AND WARRANTS - Roll-forward of the fair value of the derivative liabilities (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityTable" xlink:label="hsdt_ScheduleOfStockholdersEquityTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityTable" xlink:to="us-gaap_ClassOfWarrantOrRightAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_Warrants2022Member" xlink:label="hsdt_Warrants2022Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_Warrants2022Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CommonStockWarrantsMember" xlink:label="hsdt_CommonStockWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_CommonStockWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_StapledWarrants2025Member" xlink:label="hsdt_StapledWarrants2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_StapledWarrants2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ScheduleOfStockholdersEquityLineItems" xlink:label="hsdt_ScheduleOfStockholdersEquityLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="hsdt_ScheduleOfStockholdersEquityTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityIssues" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilitySettlements" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" xlink:label="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="hsdt_ScheduleOfStockholdersEquityLineItems" xlink:to="us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureCommonStockAndWarrantsSummaryOfRollForwardOfNumberOfSharesOfCommonStockUnderlyingWarrantsIssuedDetails" xlink:type="extended" xlink:title="99940613 - Disclosure - COMMON STOCK AND WARRANTS - Summary of roll-forward of number of shares of common stock underlying warrants issued (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightTable" xlink:label="us-gaap_ClassOfWarrantOrRightTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightTable" xlink:to="us-gaap_ClassOfWarrantOrRightAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PreFundedWarrants2025Member" xlink:label="hsdt_PreFundedWarrants2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_PreFundedWarrants2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_StapledWarrants2025Member" xlink:label="hsdt_StapledWarrants2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_StapledWarrants2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_BaseAdvisorWarrantsMember" xlink:label="hsdt_BaseAdvisorWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_BaseAdvisorWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_Warrants2022Member" xlink:label="hsdt_Warrants2022Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_Warrants2022Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CommonStockWarrantsMember" xlink:label="hsdt_CommonStockWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_CommonStockWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_OtherEquityWarrantsMember" xlink:label="hsdt_OtherEquityWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_OtherEquityWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ClassOfWarrantOrRightTable" xlink:to="srt_RangeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="srt_RangeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightLineItems" xlink:label="us-gaap_ClassOfWarrantOrRightLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightOutstanding" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightOutstanding" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ClassOfWarrantOrRightIssued" xlink:label="hsdt_ClassOfWarrantOrRightIssued" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="hsdt_ClassOfWarrantOrRightIssued" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ClassOfWarrantOrRightExercised" xlink:label="hsdt_ClassOfWarrantOrRightExercised" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="hsdt_ClassOfWarrantOrRightExercised" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ClassOfWarrantOrRightExpired" xlink:label="hsdt_ClassOfWarrantOrRightExpired" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="hsdt_ClassOfWarrantOrRightExpired" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_StockIssuedDuringPeriodSharesWarrantExercised" xlink:label="hsdt_StockIssuedDuringPeriodSharesWarrantExercised" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ClassOfWarrantOrRightLineItems" xlink:to="hsdt_StockIssuedDuringPeriodSharesWarrantExercised" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureStockBasedCompensationPlanInformationDetails" xlink:type="extended" xlink:title="99940701 - Disclosure - STOCK-BASED COMPENSATION - Plan information (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis" xlink:label="us-gaap_PlanNameAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_PlanNameAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_TwoThousandTwentyOneInducementPlanMember" xlink:label="hsdt_TwoThousandTwentyOneInducementPlanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PlanNameDomain" xlink:to="hsdt_TwoThousandTwentyOneInducementPlanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_EquityIncentive2022PlanMember" xlink:label="hsdt_EquityIncentive2022PlanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PlanNameDomain" xlink:to="hsdt_EquityIncentive2022PlanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ShareBasedCompensationAnnualIncreaseInAuthorizedSharesAsPercentageOfFullyDilutedSharesOfCommonStockOutstanding" xlink:label="hsdt_ShareBasedCompensationAnnualIncreaseInAuthorizedSharesAsPercentageOfFullyDilutedSharesOfCommonStockOutstanding" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="hsdt_ShareBasedCompensationAnnualIncreaseInAuthorizedSharesAsPercentageOfFullyDilutedSharesOfCommonStockOutstanding" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/20220331/taxonomy/role/DisclosureStockBasedCompensationAwardsGrantedAndOutstandingDetails" xlink:type="extended" xlink:title="99940702 - Disclosure - STOCK-BASED COMPENSATION - Awards granted and outstanding (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis" xlink:label="us-gaap_PlanNameAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_PlanNameAxis" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameDomain" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_EquityIncentive2022PlanMember" xlink:label="hsdt_EquityIncentive2022PlanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_PlanNameDomain" xlink:to="hsdt_EquityIncentive2022PlanMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_TwoThousandTwentyOneInducementPlanMember" xlink:label="hsdt_TwoThousandTwentyOneInducementPlanMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_PlanNameDomain" xlink:to="hsdt_TwoThousandTwentyOneInducementPlanMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_AwardTypeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="us-gaap_EmployeeStockOptionMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember" xlink:label="us-gaap_RestrictedStockUnitsRSUMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_RestrictedStockUnitsRSUMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="srt_RangeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="srt_RangeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/20220331/taxonomy/role/DisclosureStockBasedCompensationFairValueAssumptionsAndOtherDetails" xlink:type="extended" xlink:title="99940703 - Disclosure - STOCK-BASED COMPENSATION - Fair value assumptions and other (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:to="us-gaap_AwardTypeAxis" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="us-gaap_EmployeeStockOptionMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsWeightedAverageVolatilityRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" xlink:label="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/20220331/taxonomy/role/DisclosureStockBasedCompensationStockBasedCompensationExpenseDetails" xlink:type="extended" xlink:title="99940704 - Disclosure - STOCK-BASED COMPENSATION - Stock-based compensation expense (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:label="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis" xlink:label="us-gaap_IncomeStatementLocationAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" xlink:to="us-gaap_IncomeStatementLocationAxis" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain" xlink:label="us-gaap_IncomeStatementLocationDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_IncomeStatementLocationAxis" xlink:to="us-gaap_IncomeStatementLocationDomain" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpenseMember" xlink:label="us-gaap_ResearchAndDevelopmentExpenseMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_ResearchAndDevelopmentExpenseMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfSalesMember" xlink:label="us-gaap_CostOfSalesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_CostOfSalesMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember" xlink:label="us-gaap_SellingGeneralAndAdministrativeExpensesMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_IncomeStatementLocationDomain" xlink:to="us-gaap_SellingGeneralAndAdministrativeExpensesMember" priority="2" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable" priority="2" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="us-gaap_AllocatedShareBasedCompensationExpense" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureBasicAndDilutedLossPerSharePublicOfferingDetails" xlink:type="extended" xlink:title="99940802 - Disclosure - BASIC AND DILUTED LOSS PER SHARE - Public Offering (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSubsidiaryOrEquityMethodInvesteeTable" xlink:label="us-gaap_ScheduleOfSubsidiaryOrEquityMethodInvesteeTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfSubsidiaryOrEquityMethodInvesteeTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PublicOffering2024Member" xlink:label="hsdt_PublicOffering2024Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="hsdt_PublicOffering2024Member" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_Pipe2025OfferingsMember" xlink:label="hsdt_Pipe2025OfferingsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="hsdt_Pipe2025OfferingsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfSubsidiaryOrEquityMethodInvesteeTable" xlink:to="us-gaap_ClassOfWarrantOrRightAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PreFundedWarrantsMember" xlink:label="hsdt_PreFundedWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_PreFundedWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PreFundedWarrants2025Member" xlink:label="hsdt_PreFundedWarrants2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_PreFundedWarrants2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems" xlink:label="us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems" xlink:to="us-gaap_ScheduleOfSubsidiaryOrEquityMethodInvesteeTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" xlink:label="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByWarrantsOrRights" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_SaleOfStockCombinedOfferingPricePerShare" xlink:label="hsdt_SaleOfStockCombinedOfferingPricePerShare" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems" xlink:to="hsdt_SaleOfStockCombinedOfferingPricePerShare" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_SaleOfStockPreFundedWarrantsAndAccompanyingPublicWarrantsPricePerShare" xlink:label="hsdt_SaleOfStockPreFundedWarrantsAndAccompanyingPublicWarrantsPricePerShare" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems" xlink:to="hsdt_SaleOfStockPreFundedWarrantsAndAccompanyingPublicWarrantsPricePerShare" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" xlink:label="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ClassOfWarrantOrRightExercised" xlink:label="hsdt_ClassOfWarrantOrRightExercised" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems" xlink:to="hsdt_ClassOfWarrantOrRightExercised" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightOutstanding" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightOutstanding" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureBasicAndDilutedLossPerShareAntidilutiveSecuritiesDetails" xlink:type="extended" xlink:title="99940803 - Disclosure - BASIC AND DILUTED LOSS PER SHARE - Antidilutive securities (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:label="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain" xlink:label="us-gaap_AntidilutiveSecuritiesNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis" xlink:to="us-gaap_AntidilutiveSecuritiesNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="us-gaap_EmployeeStockOptionMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="us-gaap_EmployeeStockOptionMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WarrantMember" xlink:label="us-gaap_WarrantMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AntidilutiveSecuritiesNameDomain" xlink:to="us-gaap_WarrantMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PublicOffering2025Member" xlink:label="hsdt_PublicOffering2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="hsdt_PublicOffering2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis" xlink:label="us-gaap_ClassOfWarrantOrRightAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" xlink:to="us-gaap_ClassOfWarrantOrRightAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain" xlink:label="us-gaap_ClassOfWarrantOrRightDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightAxis" xlink:to="us-gaap_ClassOfWarrantOrRightDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CommonStockWarrantsMember" xlink:label="hsdt_CommonStockWarrantsMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_ClassOfWarrantOrRightDomain" xlink:to="hsdt_CommonStockWarrantsMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" xlink:label="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightOutstanding" xlink:label="us-gaap_ClassOfWarrantOrRightOutstanding" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="us-gaap_ClassOfWarrantOrRightOutstanding" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ShareMultiplierOnWarrantExercise" xlink:label="hsdt_ShareMultiplierOnWarrantExercise" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems" xlink:to="hsdt_ShareMultiplierOnWarrantExercise" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureRelatedPartiesStrategicAdvisoryAgreementTradingAdvisoryAgreementDetails" xlink:type="extended" xlink:title="99940901 - Disclosure - RELATED PARTIES - Strategic Advisory Agreement &amp; Trading Advisory Agreement (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:label="us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_Pipe2025OfferingsStrategicAdvisoryAgreementMember" xlink:label="hsdt_Pipe2025OfferingsStrategicAdvisoryAgreementMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="hsdt_Pipe2025OfferingsStrategicAdvisoryAgreementMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_Pipe2025OfferingsTradingAdvisoryAgreementMember" xlink:label="hsdt_Pipe2025OfferingsTradingAdvisoryAgreementMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="hsdt_Pipe2025OfferingsTradingAdvisoryAgreementMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis" xlink:label="srt_CounterpartyNameAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="srt_CounterpartyNameAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain" xlink:label="srt_RepurchaseAgreementCounterpartyNameDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_CounterpartyNameAxis" xlink:to="srt_RepurchaseAgreementCounterpartyNameDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_SummerWisdomHoldingsLimitedMember" xlink:label="hsdt_SummerWisdomHoldingsLimitedMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="hsdt_SummerWisdomHoldingsLimitedMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_PanteraCapitalManagementLpMember" xlink:label="hsdt_PanteraCapitalManagementLpMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RepurchaseAgreementCounterpartyNameDomain" xlink:to="hsdt_PanteraCapitalManagementLpMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementScenarioAxis" xlink:label="srt_StatementScenarioAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="srt_StatementScenarioAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain" xlink:label="srt_ScenarioUnspecifiedDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_StatementScenarioAxis" xlink:to="srt_ScenarioUnspecifiedDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_AssetsManagedLessThan1BillionMember" xlink:label="hsdt_AssetsManagedLessThan1BillionMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_ScenarioUnspecifiedDomain" xlink:to="hsdt_AssetsManagedLessThan1BillionMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_AssetsManagedBetween1BillionTo5BillionMember" xlink:label="hsdt_AssetsManagedBetween1BillionTo5BillionMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_ScenarioUnspecifiedDomain" xlink:to="hsdt_AssetsManagedBetween1BillionTo5BillionMember" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_AssetsManagedMoreThan5BillionMember" xlink:label="hsdt_AssetsManagedMoreThan5BillionMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="srt_ScenarioUnspecifiedDomain" xlink:to="hsdt_AssetsManagedMoreThan5BillionMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="srt_RangeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="srt_RangeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember" xlink:label="srt_MinimumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MinimumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:label="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="5" xlink:from="us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" xlink:to="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain" xlink:label="us-gaap_RelatedPartyDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_RelatedPartyTransactionsByRelatedPartyAxis" xlink:to="us-gaap_RelatedPartyDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyMember" xlink:label="us-gaap_RelatedPartyMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_RelatedPartyDomain" xlink:to="us-gaap_RelatedPartyMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockLineItems" xlink:label="us-gaap_SubsidiarySaleOfStockLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_SubsidiaryOrEquityMethodInvesteeSaleOfStockBySubsidiaryOrEquityInvesteeTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_TermOfAgreement" xlink:label="hsdt_TermOfAgreement" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="hsdt_TermOfAgreement" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_RenewalTermOfAgreement" xlink:label="hsdt_RenewalTermOfAgreement" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="hsdt_RenewalTermOfAgreement" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ManagementAndServiceFeesRate" xlink:label="us-gaap_ManagementAndServiceFeesRate" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_ManagementAndServiceFeesRate" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_ThresholdInvestmentForCalculatingAssetManagementFee" xlink:label="hsdt_ThresholdInvestmentForCalculatingAssetManagementFee" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="hsdt_ThresholdInvestmentForCalculatingAssetManagementFee" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ManagementFeeExpense" xlink:label="us-gaap_ManagementFeeExpense" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_ManagementFeeExpense" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsPayableCurrent" xlink:label="us-gaap_AccountsPayableCurrent" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_SubsidiarySaleOfStockLineItems" xlink:to="us-gaap_AccountsPayableCurrent" priority="1" use="optional" />
  </definitionLink>
  <definitionLink xlink:role="http://www.heliusmedical.com/role/DisclosureSubsequentEventsDetails" xlink:type="extended" xlink:title="99941001 - Disclosure - SUBSEQUENT EVENTS (Details)" xmlns="http://www.xbrl.org/2003/linkbase">
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTable" xlink:label="us-gaap_SubsequentEventTable" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="us-gaap_SubsequentEventTypeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="1" xlink:from="us-gaap_SubsequentEventTable" xlink:to="us-gaap_SubsequentEventTypeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="us-gaap_SubsequentEventTypeDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsequentEventTypeAxis" xlink:to="us-gaap_SubsequentEventTypeDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventMember" xlink:label="us-gaap_SubsequentEventMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SubsequentEventTypeDomain" xlink:to="us-gaap_SubsequentEventMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsidiarySaleOfStockAxis" xlink:label="us-gaap_SubsidiarySaleOfStockAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="2" xlink:from="us-gaap_SubsequentEventTable" xlink:to="us-gaap_SubsidiarySaleOfStockAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockNameOfTransactionDomain" xlink:label="us-gaap_SaleOfStockNameOfTransactionDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_SubsidiarySaleOfStockAxis" xlink:to="us-gaap_SaleOfStockNameOfTransactionDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_AtMarketOffering2025Member" xlink:label="hsdt_AtMarketOffering2025Member" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_SaleOfStockNameOfTransactionDomain" xlink:to="hsdt_AtMarketOffering2025Member" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis" xlink:label="srt_RangeAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="3" xlink:from="us-gaap_SubsequentEventTable" xlink:to="srt_RangeAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember" xlink:label="srt_RangeMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="srt_RangeAxis" xlink:to="srt_RangeMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember" xlink:label="srt_MaximumMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="srt_RangeMember" xlink:to="srt_MaximumMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="us-gaap_StatementEquityComponentsAxis" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" order="4" xlink:from="us-gaap_SubsequentEventTable" xlink:to="us-gaap_StatementEquityComponentsAxis" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" order="1" xlink:from="us-gaap_StatementEquityComponentsAxis" xlink:to="us-gaap_EquityComponentDomain" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember" xlink:label="us-gaap_CommonStockMember" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="1" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_CommonStockMember" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubsequentEventLineItems" xlink:label="us-gaap_SubsequentEventLineItems" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" order="1" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_SubsequentEventTable" use="optional" xbrldt:contextElement="segment" xbrldt:closed="true" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CryptoAssetNumberOfUnitsPurchased" xlink:label="hsdt_CryptoAssetNumberOfUnitsPurchased" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="2" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="hsdt_CryptoAssetNumberOfUnitsPurchased" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CryptoAssetPurchasePricePerUnit" xlink:label="hsdt_CryptoAssetPurchasePricePerUnit" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="3" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="hsdt_CryptoAssetPurchasePricePerUnit" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CryptoAssetNumberOfUnits" xlink:label="us-gaap_CryptoAssetNumberOfUnits" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="4" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_CryptoAssetNumberOfUnits" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CryptoAssetFairValuePerUnit" xlink:label="hsdt_CryptoAssetFairValuePerUnit" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="5" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="hsdt_CryptoAssetFairValuePerUnit" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="hsdt-20250930.xsd#hsdt_CryptoAssetFairValueDeclinePercentage" xlink:label="hsdt_CryptoAssetFairValueDeclinePercentage" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="6" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="hsdt_CryptoAssetFairValueDeclinePercentage" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues" xlink:label="us-gaap_StockIssuedDuringPeriodSharesNewIssues" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="7" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_StockIssuedDuringPeriodSharesNewIssues" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SaleOfStockConsiderationReceivedOnTransaction" xlink:label="us-gaap_SaleOfStockConsiderationReceivedOnTransaction" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="8" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_SaleOfStockConsiderationReceivedOnTransaction" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StockRepurchaseProgramAuthorizedAmount1" xlink:label="srt_StockRepurchaseProgramAuthorizedAmount1" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="9" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="srt_StockRepurchaseProgramAuthorizedAmount1" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="10" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare" priority="1" use="optional" />
    <loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockRepurchasedDuringPeriodValue" xlink:label="us-gaap_StockRepurchasedDuringPeriodValue" />
    <definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" order="11" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_StockRepurchasedDuringPeriodValue" priority="1" use="optional" />
  </definitionLink>
</link:linkbase>
