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Abstract:
Primate electrophysiological and lesion studies indicate a prominent role of the left dorsal premotor cortex (PMd) in action selection based on learned sensorimotor associations. Here we applied transcranial magnetic stimulation (TMS) to human left PMd at low or high intensity while right-handed individuals performed externally paced sequential key presses with their left hand. Movements were cued by abstract visual stimuli, and subjects either freely selected a key press or responded according to a prelearned visuomotor mapping rule. Continuous arterial spin labeling was interleaved with TMS to directly assess how stimulation of left PMd modulates task-related brain activity depending on the mode of movement selection. Relative to passive viewing, both tasks activated a frontoparietal motor network. Compared with low-intensity TMS, high-intensity TMS of left PMd was associated with an increase in activity in medial and right premotor areas without affecting task performance. Critically, this increase in task-related activity was only present when movement selection relied on arbitrary visuomotor associations but not during freely selected movements. Psychophysiological interaction analysis revealed a context-specific increase in functional coupling between the stimulated left PMd and remote right-hemispheric and mesial motor regions that was only present during arbitrary visuomotor mapping. Our TMS perturbation approach yielded causal evidence that the left PMd is implicated in mapping external cues onto the appropriate movement in humans. Furthermore, the data suggest that the left PMd may transiently form a functional network together with right-hemispheric and mesial motor regions to sustain visuomotor mapping performed with the left nondominant hand.
