Distinct hindlimb motor cortex subregions encode forward and backward hindlimb movements in rats.

INTRODUCTION: The motor cortex is organized to coordinate voluntary movements through distinct subregions that control different parts of the body. Intracortical microstimulation (ICMS) with long-duration trains (LD-ICMS) can uncover complex, behaviorally relevant movement patterns that differ from the simple, joint-specific responses evoked by conventional short-duration trains (SD-ICMS). While previous studies have primarily examined forelimb representations, the organization of hindlimb movements remains less understood.

METHODS: Here, we characterized hindlimb movements evoked by LD-ICMS, analyzing their kinematic features, cortical location and functional relevance in rats.

RESULTS: Two distinct complex movements, Advance and Elevation, were identified, each with unique kinematic signatures. Principal component analysis revealed that overall movement amplitude and joint flexion patterns underlying movement trajectory systematically distinguished the two movement types. Advance and Elevation movements were spatially segregated within anteromedial and posterolateral cortical subregions, respectively. Phase-coherent stimulation of these subregions during locomotion selectively biased hindlimb trajectories forward or backward in an amplitude-dependent manner.

DISCUSSION: These results demonstrate that the rat hindlimb motor cortex contains distinct subregions specialized for directionally specific and functionally relevant movement control.