Modification of cortical somatosensory evoked potentials during tactile exploration and simple active and passive movements.

The present study compares the effects of different types of movement on median nerve somatosensory evoked potentials (SEPs) recorded from frontal, central and parietal electrodes. Test conditions included tactile exploratory movements, repetitive active and passive thumb movements and isometric contraction. All these conditions modified the SEPs in a similar manner. Parietal N20, P25, and N60, central P22 and N32, and frontal N25, N30 and P40 deflections were diminished, while later centro-parietal P40 and fronto-central N60 were unchanged. A small frontal P35 emerged during movement. The subcortical P14 was not changed in any of the conditions. The similar modulatory effects of simple active movements and of tactile exploration indicate that the modification of SEPs does not depend on the importance of proprioceptive feedback information for movement execution. As all modulatory effects were present also during passive movement, these observed effects are most likely to be caused by afferent occlusion in the ascending thalamo-cortical pathways or sensorimotor cortical cell populations.