MODULATION OF SOMATOSENSORY-EVOKED POTENTIALS DURING COORDINATION BETWEEN POSTURE AND MOVEMENT

Somatosensory evoked potentials (SEPs) elicited during execution of vo luntary movements undergo modification in their amplitude ('gating'). We have studied SEP changes during a motor task that includes anticipa tory postural adjustment and focal movement. Upright standing subjects were performing fast forward elevation of one arm. The electrical sti mulus was presented over the ipsilateral posterior tibial nerve within two different time frames: (1) preceding the EMG activity of femoral biceps muscle, known to be first in occurrence in such task; (2) durin g this EMG activity, yet before the EMG occurrence in anterior deltoid muscle - prime mover for the forward arm elevation. The following sig nificant changes in SEPs preceding focal movements as compared with co ntrol SEPs during quiet stance were found: The early component P42-N50 showed a marked decrease, regardless of its time relation to the anti cipatory activity in the leg. Component N50-P60 increased in amplitude , more so when elicited within an earlier time frame. Thus, diminution of amplitude as an expression of gating, was found to exist already b efore the occurrence of anticipatory postural adjustment activity and to persist during the ensuing focal movement.