Reward anticipation modulates primary motor cortex excitability during task preparation.

Task preparation has been associated with a transient suppression of corticospinal excitability (CSE) before target onset, but it is an open question to what extent CSE suppression during task preparation is susceptible to motivational factors. Here, we examined whether CSE suppression is modulated by reward anticipation, and, if so, how this modulation develops over time. We administered a cue-target delay paradigm in which 1000ms before target onset a cue was presented indicating whether or not reward could be obtained for fast and accurate responses in a Simon task. Single-pulse transcranial magnetic stimulation was applied over left primary motor cortex (M1) during the delay period (400, 600, or 800ms after cue onset) or 200ms after target onset, and electromyography was obtained from the right first dorsal interosseous muscle. Behaviorally, the anticipation of reward improved performance (i.e. faster reaction times). Most importantly, during reward anticipation we observed a linear decrease of motor evoked potential amplitudes that was absent when no reward was anticipated. This suggests that reward anticipation modulates CSE during task preparation.