Momentary reward induce changes in excitability of primary motor cortex

ObjectiveTo investigate the human primary motor cortex (M1) excitability changes induced by momentary reward.MethodsTo test the changes in excitatory and inhibitory functions of M1, motor-evoked potentials (MEPs), short-interval intracortical inhibition (SICI) and short-latency afferent inhibition (SAI) were tested in the abductor pollicis brevis (APB) muscle of non-dominant hand in 14 healthy volunteers by transcranial magnetic stimulation (TMS) during a behavioral task in which subjects were pseudorandomly received either reward target or non-target stimuli in response to a cue. To control sensorimotor and attention effects, a sensorimotor control task was done replacing the reward target with non-reward target.ResultsThe SICI was increased, and the SAI was decreased significantly during the presentation of the reward target stimuli. Those changes were not evident during non-reward target stimuli in the sensorimotor control task, indicating that this change is specific to momentary reward.ConclusionsMomentary rewarding is associated with change in intracortical inhibitory circuits of M1. Significance: TMS may be a useful probe to study the reward system in health and in many diseases in which its dysfunction is suspected.

Research highlights
► By using transcranial magnetic stimulation (TMS), we tested the primary motor cortex (M1) function during the processing of the momentary reward signals.
► We found the increased intracortical inhibition and decreased afferent inhibition of M1 in response to the momentary reward signals.
► Our findings suggest the existence of the reward-related function of human M1.