[Corticospinal excitabillity during vibratory reaction of forearm muscles in man].

We investigated the effects of forearm flexor/extensor muscles vibration on corticospinal excitability by means of transcranial magnetic stimulation (TMS) in healthy subjects. Motor evoked potentials (MEPs) and ongoing baseline activity of forearm flexor and extensor muscles were analyzed during muscle activity increase produced by vibration of these muscles (Tonic Vibratory Reflex) and by antagonist muscle vibration in isometrical condition (Antagonist Vibratory Response) and during voluntary contraction. The results showed that the normalized MEPs of forearm flexor increased by 66% during TVR, by 75% during AVR, and by 18% during voluntary contraction of this muscle as compared to threshold value. However, the increase in MEP response produced by vibratory reactions in wrist muscles did not significantly differ from that produced by the voluntary contraction of these muscles unlike the MEP response change during vibratory and voluntary activation of the forearm muscles in our previous article. Different involvement of the motor cortex in the control of vibratory reactions of the distal and proximal muscles is discussed.