Functional interaction between human dorsal premotor cortex and the ipsilateral primary motor cortex for grasp plans: A dual-site TMS study
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Recent findings suggest that the dorsal premotor cortex (PMd), a cortical area in the dorsomedial pathway, is involved in grasp control. It is unclear, however, whether human PMd transfers grasp-related information to the primary motor cortex hand area (M1 HAND) during action preparation. The present study tested whether ipsilateral cortico-cortical connections between PMd and M1 HAND in the left hemisphere are modulated during grasp preparation. Ten participants performed object-directed grasps and reaches with the right hand. Functional connectivity between left PMd and ipsilateral M1 HAND was probed with dual-site transcranial magnetic stimulation. We found that PMd-M1 HAND functional interactions were facilitated selectively for the muscles involved in the preparation of the upcoming grasps. The PMd-M1 HAND interaction was facilitated for first dorsal interosseous muscle for both precision grip and whole-hand grasps and for abductor digiti minimi muscle for whole-hand grasps. We conclude that human dorsomedial PMd-M1 HAND circuit encodes handgrip formation during grasp preparation.