Premovement gating of somatosensory evoked potentials after tibial nerve stimulation.

Somatosensory evoked potentials (SEPs) are attenuated or gated during movement. The mechanism for this includes both centrifugal gating of afferent input and competition with other afferents caused by the movement (peripheral gating). Using a paradigm in which the signal for triggering movement is the electric stimulus for SEPs, we studied the gating of SEPs after tibial nerve stimulation prior to foot movement, and compared it with that during counting task. Significant gating was found for P40 component, which distributed centrally and ipsilaterally to the side of the stimulation, whereas the contralateral N40 component showed no changes. Dissociated gating of P40 and N40 indicates multiple generators of these components, in contrast to the previous view of a single generator dipole projecting tangentially. Together with the previous findings in median SEPs, these gating phenomena should represent a general mechanism for sensori-motor integration in preparation for limb movement.