Stimulus-related 20-Hz activity of human cortex modulated by the way of presenting hand actions.

The neural mechanisms underlying recognition of presented hand actions are not well understood. Rolandic rhythmic activity of about 20 Hz is reproducibly induced after median nerve stimulation and has been reported to be related to various types of movements including actual movement, motor imagery and action observation. We recorded neuromagnetic brain activity from 11 healthy subjects to investigate whether the way to present hand actions modulates the 20-Hz activity after median nerve stimulation. The stimulus-related 20-Hz activity was prominently evoked in the contralateral sensorimotor cortex around 0.5-1.0 s after median nerve stimulation and was almost completely suppressed during executing actual hand action. The suppression of the stimulus-related 20-Hz activity was also observed during viewing the similar action of another person's hand. Furthermore, the suppression during viewing the action of another person's hand presented in the same direction as the subject's hand was significantly larger than that during viewing it presented in the opposite direction and was closer to that during executing subject's own hand action. These results indicate that the stimulus-related rolandic 20-Hz activity was modulated by the way to present hand actions, and suggest that the 20-Hz activity is related to neural mechanisms underlying recognition of presented hand actions.