Summary
Understanding how the body is represented in motor cortex is key to understanding how the brain controls movement. The precentral gyrus (PCG) has long been thought to contain largely distinct regions for the arm, leg and face (represented by the “motor homunculus”). However, mounting evidence has begun to reveal a more intermixed, interrelated and broadly tuned motor map. Here, we revisit the motor homunculus using microelectrode array recordings from 20 arrays that broadly sample PCG across 8 individuals, creating a comprehensive map of human motor cortex at single neuron resolution. We found whole-body representations throughout all sampled points of PCG, contradicting traditional leg/arm/face boundaries. We also found two speech-preferential areas with a broadly tuned, orofacial-dominant area in between them, previously unaccounted for by the homunculus. Throughout PCG, movement representations of the four limbs were interlinked, with homologous movements of different limbs (e.g., toe curl and hand close) having correlated representations. Our findings indicate that, while the classic homunculus aligns with each area’s preferred body region at a coarse level, at a finer scale, PCG may be better described as a mosaic of functional zones, each with its own whole-body representation.
Competing Interest Statement
The MGH Translational Research Center has a clinical research support agreement (CRSA) with Axoft, Neuralink, Neurobionics, Precision Neuro, Synchron, and Reach Neuro, for which LRH provides consultative input. LRH is a co-investigator on an NIH SBIR grant with Paradromics, and is a non-compensated member of the Board of Directors of a nonprofit assistive communication device technology foundation (Speak Your Mind Foundation). Mass General Brigham (MGB) is convening the Implantable Brain-Computer Interface Collaborative Community (iBCI-CC); charitable gift agreements to MGB, including those received to date from Paradromics, Synchron, Precision Neuro, Neuralink, and Blackrock Neurotech, support the iBCI-CC, for which LRH provides effort. JMH is a consultant for Neuralink and Paradromics, serves on the Medical Advisory Board of Enspire DBS and is a shareholder in Maplight Therapeutics. He is also an inventor on intellectual property licensed by Stanford University to Blackrock Neurotech and Neuralink Corp. SDS is an inventor on intellectual property licensed by Stanford University to Blackrock Neurotech and Neuralink Corp. He is currently an advisor to ALVI Labs. FRW is an inventor on intellectual property licensed by Stanford University to Blackrock Neurotech and Neuralink Corp. CP is a consultant for Meta (Reality Labs) and Synchron. DMB is a surgical consultant for Paradromics Inc. SDS, DMB, and MW are inventors of intellectual property related to neuroprostheses owned by the University of California, Davis. All other authors have no competing interests.