The somatosensory-evoked potential in reaction time is gated and elicited earlier when the motor response to a somatosensory cue is faster.

The aim of this study was to investigate whether the somatosensory-evoked potential (SEP) is gated and elicited earlier when a motor response to a somatosensory stimulus is faster. In healthy humans, the left index finger and thumb were pinched in response to a somatosensory stimulus administered over the left median nerve. The SEP elicited by this stimulus when producing a fast motor response was compared with that when producing a slow motor response. The amplitudes of N18 and frontal P40 when producing a fast motor response were smaller than those when producing a slow motor response. The latencies of frontal P22 and P40 when producing a fast motor response were shorter than those when producing a slow motor response. These findings indicated that the responses of the primary sensory and frontal areas elicited by a somatosensory stimulus are gated and that the responses of the frontal areas elicited by this stimulus occur earlier when a motor response to this stimulus is faster. The enhanced efficiency or increased speed of the stimulus identification process may be related to the gating and early onset of the SEP components when producing a fast motor response.