“Characteristics and stability of sensorimotor activity driven by isolated-muscle group activation in a human with tetraplegia”

ABSTRACT Understanding cortical movement representations and their stability can shed light on robust brain-machine interface (BMI) approaches to decode these representations without frequent recalibration. Here, we characterize the spatial organization (somatotopy) and stability of the bilateral sensorimotor map of forearm muscles in an incomplete-high spinal-cord injury study participant implanted bilaterally in the primary motor and sensory cortices with Utah microelectrode arrays (MEAs). We built the map by recording multiunit activity (MUA) and surface electromyography (EMG) as the participant executed (or attempted) contractions of 2 wrist muscles on each side of the body. To assess stability, we repeatedly mapped and compared left--wrist--extensor-related activity throughout several sessions, comparing somatotopy of active electrodes and neural signals both at the within-electrode (multiunit) and cross-electrode (network) levels. Body maps showed significant activation in motor and sensory cortical electrodes, with fractured, intermixed representations of both intact and paralytic muscles. Within electrodes, firing strength stability decreased with time, with higher stability observed in sensory cortex than in motor, and in the contralateral hemisphere than in the ipsilateral. However, we observed no differences at network level, and no evidence of decoding instabilities for wrist EMG, either across timespans of hours or days, or across recording area. These results demonstrate first-time construction of a bilateral human sensorimotor map with MEAs. Further, while map stability differs between brain area and hemisphere at multiunit/electrode level, these differences are nullified at ensemble level.