Conditioning transcranial magnetic stimulation of ventral premotor cortex shortens simple reaction time.

The ventral premotor cortex (PMv) is a key area of the sensorimotor control loop, it subtends complex motor sequences, especially when the hand is involved. However, its specific contribution to simple motor response to sensory cue is still not completely clear. To investigate the role of PMv, we used transcranial magnetic stimulation (TMS) to interfere with its function during a simple reaction time (SRT) task. We ran two experiments where participants were required to respond as fast as possible to a median nerve stimulation (go-signal), while sub-M1-threshold single pulse TMS was delivered either on left (contralateral) PMv or right (ipsilateral to sensory stimulus and motor response) PMv, 5-65 ms after the go-signal. TMS delivered on either PMv up to 25 ms after the go-signal shortened reaction time. This is the time window compatible with the arrive of sensory afferences, as if conditioning before sensory afferences arrive lower the threshold needed to release the pre-planned motor program to the primary motor cortex. This is in line with a putative PMv function of buffer of pre-planned motor program not strictly lateralized in one hemisphere.