SELECTIVE GATING OF LOWER-LIMB CORTICAL SOMATOSENSORY-EVOKED POTENTIALS (SEPS) DURING PASSIVE AND ACTIVE FOOT MOVEMENTS

We evaluated subcortical and cortical somatosensory evoked potentials (SEPs) in response to posterior tibial nerve stimulation in 4 experime ntal conditions of foot movement and compared them with the baseline c ondition of full relaxation. The experimental conditions were: (a) act ive flexion-extension of the stimulated foot; (b) active flexion-exten sion of the non-stimulated foot; (c) passive flexion-extension of the stimulated fool in complete relaxation; (d) tonic active flexion of th e stimulated foot. We analyzed latencies and amplitudes of the subcort ical P30 potential, of the contralateral pre-rolandic N37 and P50 resp onses and of the P37, N50 and P60 potentials recorded over the vertex. Latencies did not vary in any of the paradigms. The amplitude of subc ortical P30 potential did not change during any of the paradigms. Amon g the cortical waves, P37, N50 and P60 amplitudes were significantly a ttenuated in all conditions except active movement of the non-stimulat ed foot (b). This attenuation was less during passive (c) than during active movements of the stimulated foot (a and d). The contralateral p re-rolandic waves N37 and P50 showed no significant decrease during an y of the paradigms. These results suggest that gating occurs rostrally to the cervico-medullary junction, probably at cortical level. The di fferent behavior of N37, P50 and P37, N50 cortical responses during mo vement of the stimulated foot provides evidence suggestive of a highly localized gating process occurring al cortical level. These potential s could reflect activation of separate, functionally distinct generato rs. (C) 1997 Elsevier Science Ireland Ltd.