Changes of somatosensory evoked potentials preceding rapid voluntary movement in Go/No-go choice reaction time task

To elucidate the sensorimotor mechanisms in preparation of voluntary movement, we examined the changes of the somatosensory evoked potentials (SEPs) following median nerve stimulation in Go/No-go choice-reaction time task. Eleven normal subjects performed extension of the middle finger according to the Go signal while they did not make any movement and relaxed on the No-go and Control signals, respectively. Each signal was randomly presented on a computer screen in front of the subject. Single pulse stimulation was applied to the right median nerve at 150 ms after the response signal in each Go/No-go and Control sequence so as to be just before the voluntary movement in the Go sequence. The SEPs were recorded from F3, C3' (midpoint between P3 and C3) and P3 on the left hemisphere. In comparison with the Control sequence, the amplitude of N20 and P25 recorded from C3' and P3 was significantly attenuated before movement in the Go sequence (P<0.02, ANOVA with Bonferroni-Dunn post hoc procedure). On the other hand, the parietal N33 and frontal N30 were attenuated in both Go and No-go sequences (P<0.02). None of the SEP components were changed when the stimulus was delivered before the response signal. We speculate that the attenuation of N20 was linked with the activation of the motor cortex followed by the actual movement. The attenuation of other components up to 33 ms after stimulus were considered to be more related to the preparation or the attention to the voluntary movement than to the movement itself.