Transcranial magnetic stimulation on the dorsal premotor cortex facilitates human visuomotor adaptation

The premotor cortex is traditionally known to be involved in motor preparation and execution. More recently, evidence from neuroscience research shows that the dorsal premotor cortex (PMd) is also involved in sensory error-based motor adaptation and that invasive brain stimulation on PMd can attenuate adaptation in monkeys. The present study examines if adaptation can be modulated noninvasively in humans. Twenty-five healthy volunteers participated in a motor task in which rapid arm-reaching movements were made to hit a target, whereas the online cursor feedback about the hand position was visually rotated, inducing sensory error that drove motor adaptation. Transcranial magnetic stimulation (TMS) was delivered to PMd just before experiencing a sensory error, as in the previous study on monkeys. The degree of motor adaptation was measured as the change in the hand direction in response to the experienced error. TMS was found to increase adaptation compared with control conditions. Interestingly, the direction of modulation was opposite to the previous study on monkeys, which might originate from different methods and parameters of stimulation. The effect was also location-specific and was not a mere artifact of applying TMS because the facilitatory modulation occurred when stimulating PMd but not when stimulating the ventral premotor cortex, which was known for different roles and networks from PMd. Since noninvasive neuromodulation is a promising tool for research and clinical practice, the present study demonstrates that PMd is a feasible target region of neuromodulation to understand human motor adaptation and improve motor rehabilitation.