Sensorimotor integration during grasping is mediated by distinct M1 circuits

Motor control relies on the dynamic interplay between excitatory and inhibitory influences shaping sensorimotor integration during hand movements. In this study, we investigated short-latency afferent inhibition (SAI)-a neurophysiological marker of sensorimotor integration-during different isometric grasping behaviors (precision vs. power grip). We applied transcranial magnetic stimulation (TMS) with different coil orientations [antero-posterior (AP) vs. postero-anterior (PA)] to engage distinct neuronal populations within the primary motor cortex (M1). We found increased SAI in the AP direction during grasp execution and enhanced corticospinal excitability for precision grip when tested with AP stimulation. These findings provide evidence that distinct cortical circuits within M1 are differentially engaged during different hand configurations. Notably, we observe no grip-specific modulation of SAI, which may reflect a less topographically precise distribution of thalamocortical afferents-along with their lower temporal resolution, potentially shaped by cholinergic modulation. Future studies should investigate SAI dynamics across different phases (i.e., preparation vs. execution) of naturalistic prehension.<b>NEW & NOTEWORTHY</b> In the present study, we assessed SAI in M1 using different coil orientations (AP vs. PA) to determine whether distinct M1-S1 circuits are selectively engaged during rest and grasping behaviors (precision vs. power grip). We found increased SAI in the AP direction during grasp execution and greater corticospinal excitability for precision grip with AP stimulation, supporting the idea that distinct M1 circuits are differentially recruited depending on hand configuration and sensorimotor demands.