The role of PMd in voluntary motor control: insights from TMS research

Transcranial magnetic stimulation (TMS) research has furthered understanding of human PMd function due to its unrivalled ability to measure the inhibitory and facilitatory influences of PMd over M1 in a temporally precise manner. Findings from TMS research indicate that PMd transiently modulates inhibitory output to effector representations within M1 during motor preparation depending on which effectors are selected for response, and that the timing of these modulations correlates with the cognitive demands of the task. In this review, we critically assess this literature within the context of prevailing theories of PMd function borne out of single/multi unit recording research in non-human primates. Through this process we identify gaps in the literature and propose future experiments to address lingering questions.