Microscale organization and separability of upper extremity representations in the human motor homunculus

Microscale organization and separability of upper extremity representations in the human motor homunculus | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Microscale organization and separability of upper extremity representations in the human motor homunculus Iahn Cajigas, Pedro Borges, Qasim Qureshi, Pierce Davis, Zhengjia Wang, and 21 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9528027/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Understanding the microscale spatial organization of the human motor homunculus is essential for designing surface-based brain-computer interfaces (BCIs). We investigated these dynamics using the highest-density clinically available subdural microelectrode arrays (1024 channels, 400 micrometers pitch) temporarily implanted in 11 neurosurgical patients undergoing awake surgery. We mapped broadband high gamma activity (>80 Hz) during upper extremity movements across 9 joints and hand gestures (rock, paper, scissors). Gestures produced consistent, localized spatial patterns in M1/S1, revealing shared microscale hand somatotopy across participants. Joint mapping revealed somatotopic representations organized as concentrically larger activation regions from distal to proximal joints. We characterized persistent spatial gradients in high gamma activity and representational overlap at microscale resolution. While previous macroscale studies showed overlapping motor representations, our high-density recordings provided a much finer mapping of this overlap and revealed a relationship between overlap degree and decoding performance. Our findings reveal a previously unobserved microscale mapping of motor commands in M1 and S1 and suggest that finer spatial resolution is necessary to decode complex movements from the brain surface. Biological sciences/Neuroscience/Motor control/Motor cortex Biological sciences/Neuroscience/Motor control/Brain–machine interface Biological sciences/Neuroscience/Computational neuroscience/Neural encoding Biological sciences/Neuroscience/Computational neuroscience/Neural decoding brain computer interfaces neuroengineering somatotopy motor rehabilitation Full Text Additional Declarations Yes there is potential Competing Interest. ICG (corresponding author) is a Consultant Medtronic and Paradromics, research devices from Precision Neuroscience, research funding from Boston scientific. Supplementary Files extendeddatatable1.docx Extended Data Table 1 supplementalfinal.docx Supplemental Information Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9528027","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":629569985,"identity":"93d0f9f7-44ab-4cb4-9d5d-ecef337e6745","order_by":0,"name":"Iahn Cajigas","email":"data:image/png;base64,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","orcid":"https://orcid.org/0000-0002-5808-453X","institution":"University of Pennsylvania","correspondingAuthor":true,"prefix":"","firstName":"Iahn","middleName":"","lastName":"Cajigas","suffix":""},{"id":629569986,"identity":"5bb49a68-ebea-490e-a270-07f781ccfc0a","order_by":1,"name":"Pedro Borges","email":"","orcid":"","institution":"University of Pennsylvania","correspondingAuthor":false,"prefix":"","firstName":"Pedro","middleName":"","lastName":"Borges","suffix":""},{"id":629569987,"identity":"e660505f-8c2b-44a1-8e53-de1c4193265c","order_by":2,"name":"Qasim Qureshi","email":"","orcid":"","institution":"University of Pennsylvania","correspondingAuthor":false,"prefix":"","firstName":"Qasim","middleName":"","lastName":"Qureshi","suffix":""},{"id":629569988,"identity":"0c0b0936-6efe-4b40-a7c7-8c31d3533e99","order_by":3,"name":"Pierce Davis","email":"","orcid":"","institution":"University of Pennsylvania","correspondingAuthor":false,"prefix":"","firstName":"Pierce","middleName":"","lastName":"Davis","suffix":""},{"id":629569989,"identity":"9869ed92-475f-46c2-8f3e-eea43a15d727","order_by":4,"name":"Zhengjia Wang","email":"","orcid":"https://orcid.org/0000-0001-5629-1116","institution":"University of Pennsylvania School of Medicine","correspondingAuthor":false,"prefix":"","firstName":"Zhengjia","middleName":"","lastName":"Wang","suffix":""},{"id":629569990,"identity":"1a45cdde-5f19-4677-bffa-0e6e0b359748","order_by":5,"name":"Krishna Sargur","email":"","orcid":"","institution":"University of Pennsylvania","correspondingAuthor":false,"prefix":"","firstName":"Krishna","middleName":"","lastName":"Sargur","suffix":""},{"id":629569991,"identity":"55071302-5789-42c2-812e-b544ec38d6d4","order_by":6,"name":"Jarl Haggerty","email":"","orcid":"","institution":"University of Pennsylvania","correspondingAuthor":false,"prefix":"","firstName":"Jarl","middleName":"","lastName":"Haggerty","suffix":""},{"id":629569992,"identity":"67052868-ea61-4855-a7ae-399ea28631be","order_by":7,"name":"Katie Wingel","email":"","orcid":"","institution":"University of Pennsylvania","correspondingAuthor":false,"prefix":"","firstName":"Katie","middleName":"","lastName":"Wingel","suffix":""},{"id":629569993,"identity":"095664a7-21ab-45c8-8d07-ab1bed73c404","order_by":8,"name":"Min Jae Kim","email":"","orcid":"","institution":"University of Pennsylvania","correspondingAuthor":false,"prefix":"","firstName":"Min","middleName":"Jae","lastName":"Kim","suffix":""},{"id":629569994,"identity":"ec830c4a-9ea5-49cf-be4a-ac87c64d6488","order_by":9,"name":"Thomas Pisano","email":"","orcid":"","institution":"University of Pennsylvania","correspondingAuthor":false,"prefix":"","firstName":"Thomas","middleName":"","lastName":"Pisano","suffix":""},{"id":629569995,"identity":"ccb59d50-c94e-4b5c-88af-8cd41fbdd282","order_by":10,"name":"Elton Ho","email":"","orcid":"","institution":"Precision Neuroscience","correspondingAuthor":false,"prefix":"","firstName":"Elton","middleName":"","lastName":"Ho","suffix":""},{"id":629569996,"identity":"1ce79bef-676e-43a1-b98b-318516983773","order_by":11,"name":"Katrina Barth","email":"","orcid":"","institution":"Precision Neuroscience","correspondingAuthor":false,"prefix":"","firstName":"Katrina","middleName":"","lastName":"Barth","suffix":""},{"id":629569997,"identity":"b66a8f25-dfd8-4aad-871f-9ab3c1461d15","order_by":12,"name":"Yoon Woo Byun","email":"","orcid":"","institution":"Precision Neuroscience Corporation","correspondingAuthor":false,"prefix":"","firstName":"Yoon","middleName":"Woo","lastName":"Byun","suffix":""},{"id":629569998,"identity":"475ebac1-734c-4baf-898e-bed34e02a914","order_by":13,"name":"Joshua Miller","email":"","orcid":"","institution":"Precision Neuroscience","correspondingAuthor":false,"prefix":"","firstName":"Joshua","middleName":"","lastName":"Miller","suffix":""},{"id":629569999,"identity":"cb1d3d30-52f6-48a7-ae63-ca0e5bf2b62b","order_by":14,"name":"Jacqueline Dister","email":"","orcid":"","institution":"Precision Neuroscience","correspondingAuthor":false,"prefix":"","firstName":"Jacqueline","middleName":"","lastName":"Dister","suffix":""},{"id":629570000,"identity":"27f9dece-803f-4787-af0c-2bee1c204598","order_by":15,"name":"Ramin Anushiravani","email":"","orcid":"","institution":"Precision Neuroscience","correspondingAuthor":false,"prefix":"","firstName":"Ramin","middleName":"","lastName":"Anushiravani","suffix":""},{"id":629570001,"identity":"ec33d021-786a-4db8-8505-38208c5379f6","order_by":16,"name":"Mark Murphy","email":"","orcid":"","institution":"Precision Neuroscience Corporation","correspondingAuthor":false,"prefix":"","firstName":"Mark","middleName":"","lastName":"Murphy","suffix":""},{"id":629570002,"identity":"25501bc5-fe4e-4e56-828b-58a70d683cb8","order_by":17,"name":"Adam Poole","email":"","orcid":"","institution":"Precision Neuroscience","correspondingAuthor":false,"prefix":"","firstName":"Adam","middleName":"","lastName":"Poole","suffix":""},{"id":629570003,"identity":"d7650a56-d80d-4e93-916b-bf9b8c764371","order_by":18,"name":"Jayme Strauss","email":"","orcid":"","institution":"Precision Neuroscience","correspondingAuthor":false,"prefix":"","firstName":"Jayme","middleName":"","lastName":"Strauss","suffix":""},{"id":629570004,"identity":"1cb88d7f-dcba-4fd5-b274-fe4294d0bda2","order_by":19,"name":"Craig Mermel","email":"","orcid":"https://orcid.org/0000-0002-0816-3395","institution":"Precision Neuroscience","correspondingAuthor":false,"prefix":"","firstName":"Craig","middleName":"","lastName":"Mermel","suffix":""},{"id":629570005,"identity":"861817fb-0556-4f10-a39d-be21d2da0aba","order_by":20,"name":"Liming Qiu","email":"","orcid":"","institution":"University of Pennsylvania","correspondingAuthor":false,"prefix":"","firstName":"Liming","middleName":"","lastName":"Qiu","suffix":""},{"id":629570006,"identity":"9b1c601f-cf4c-4e9f-80c1-b702b0d7c55e","order_by":21,"name":"Casey Halpern","email":"","orcid":"https://orcid.org/0000-0003-3907-216X","institution":"University of Pennsylvania","correspondingAuthor":false,"prefix":"","firstName":"Casey","middleName":"","lastName":"Halpern","suffix":""},{"id":629570007,"identity":"b5b46d0a-3d57-4ea1-bc11-d2c3d323ad1a","order_by":22,"name":"Daniel Yoshor","email":"","orcid":"","institution":"University of Pennsylvania","correspondingAuthor":false,"prefix":"","firstName":"Daniel","middleName":"","lastName":"Yoshor","suffix":""},{"id":629570008,"identity":"dc40d717-1af2-4663-8c62-cccb8cdf664e","order_by":23,"name":"Michael Beauchamp","email":"","orcid":"","institution":"University of Pennsylvania","correspondingAuthor":false,"prefix":"","firstName":"Michael","middleName":"","lastName":"Beauchamp","suffix":""},{"id":629570009,"identity":"5d2e1efd-387b-42a1-9620-fe321b81276f","order_by":24,"name":"Bijan Pesaran","email":"","orcid":"","institution":"University of Pennsylvania","correspondingAuthor":false,"prefix":"","firstName":"Bijan","middleName":"","lastName":"Pesaran","suffix":""},{"id":629570010,"identity":"8f5df1a6-ed09-4895-a9fa-e70430be5a2d","order_by":25,"name":"Benjamin Rapoport","email":"","orcid":"https://orcid.org/0000-0002-0049-6419","institution":"Precision Neuroscience Corporation","correspondingAuthor":false,"prefix":"","firstName":"Benjamin","middleName":"","lastName":"Rapoport","suffix":""}],"badges":[],"createdAt":"2026-04-25 20:00:36","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9528027/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9528027/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108184528,"identity":"31f8c671-9090-4247-a7e1-769bb9835cc7","added_by":"auto","created_at":"2026-04-30 09:04:21","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2666899,"visible":true,"origin":"","legend":"","description":"","filename":"manuscriptrevisedfinal.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9528027/v1_covered_5857f4d0-87bf-4358-bc91-f3b3066b06de.pdf"},{"id":108077041,"identity":"959b372c-f069-4893-8af4-0bf85b7e27ec","added_by":"auto","created_at":"2026-04-29 07:06:28","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":3126940,"visible":true,"origin":"","legend":"Extended Data Table 1","description":"","filename":"extendeddatatable1.docx","url":"https://assets-eu.researchsquare.com/files/rs-9528027/v1/411074d5b78bfcd00e88bcff.docx"},{"id":108181317,"identity":"981c0f3c-8d63-4e51-b23d-02099f9147b1","added_by":"auto","created_at":"2026-04-30 08:58:33","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":9446295,"visible":true,"origin":"","legend":"Supplemental Information","description":"","filename":"supplementalfinal.docx","url":"https://assets-eu.researchsquare.com/files/rs-9528027/v1/19a2ed6dbbd06497ca3abd91.docx"}],"financialInterests":"\u003cb\u003eYes\u003c/b\u003e there is potential Competing Interest.\nICG (corresponding author) is a Consultant Medtronic and Paradromics, research devices from Precision Neuroscience, research funding from Boston scientific.","formattedTitle":"Microscale organization and separability of upper extremity representations in the human motor homunculus","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"brain computer interfaces, neuroengineering, somatotopy, motor rehabilitation","lastPublishedDoi":"10.21203/rs.3.rs-9528027/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9528027/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Understanding the microscale spatial organization of the human motor homunculus is essential for designing surface-based brain-computer interfaces (BCIs). We investigated these dynamics using the highest-density clinically available subdural microelectrode arrays (1024 channels, 400 micrometers pitch) temporarily implanted in 11 neurosurgical patients undergoing awake surgery. We mapped broadband high gamma activity (\u003e80 Hz) during upper extremity movements across 9 joints and hand gestures (rock, paper, scissors). Gestures produced consistent, localized spatial patterns in M1/S1, revealing shared microscale hand somatotopy across participants. Joint mapping revealed somatotopic representations organized as concentrically larger activation regions from distal to proximal joints. We characterized persistent spatial gradients in high gamma activity and representational overlap at microscale resolution. While previous macroscale studies showed overlapping motor representations, our high-density recordings provided a much finer mapping of this overlap and revealed a relationship between overlap degree and decoding performance. Our findings reveal a previously unobserved microscale mapping of motor commands in M1 and S1 and suggest that finer spatial resolution is necessary to decode complex movements from the brain surface.","manuscriptTitle":"Microscale organization and separability of upper extremity representations in the human motor homunculus","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-29 07:06:24","doi":"10.21203/rs.3.rs-9528027/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-neuroscience","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"neuro","sideBox":"Learn more about [Nature Neuroscience](http://www.nature.com/neuro/)","snPcode":"","submissionUrl":"","title":"Nature Neuroscience","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Research","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"435d7413-3f73-46df-91da-359249f1bce1","owner":[],"postedDate":"April 29th, 2026","published":true,"recentEditorialEvents":[{"type":"reviewerAgreed","content":"This content is not available.","date":"2026-05-12T16:27:31+00:00","index":2,"fulltext":"This content is not available."},{"type":"reviewerAgreed","content":"This content is not available.","date":"2026-05-12T13:19:40+00:00","index":1,"fulltext":"This content is not available."},{"type":"reviewersInvited","content":"6","date":"2026-05-12T13:00:28+00:00","index":"","fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":67012686,"name":"Biological sciences/Neuroscience/Motor control/Motor cortex"},{"id":67012687,"name":"Biological sciences/Neuroscience/Motor control/Brain\u0026#x2013;machine interface"},{"id":67012688,"name":"Biological sciences/Neuroscience/Computational neuroscience/Neural encoding"},{"id":67012689,"name":"Biological sciences/Neuroscience/Computational neuroscience/Neural decoding"}],"tags":[],"updatedAt":"2026-05-12T13:24:10+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-29 07:06:24","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9528027","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9528027","identity":"rs-9528027","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}