LASER-EVOKED POTENTIALS AFTER PAINFUL HAND AND FOOT STIMULATION IN HUMANS - EVIDENCE FOR GENERATION OF THE MIDDLE-LATENCY COMPONENT IN THE SECONDARY SOMATOSENSORY CORTEX

The vertex potential (N2, P2) of the laser-evoked potential (LEP) is p receded by a small negativity (N1). The role of the secondary somatose nsory cortex (SII) in generation of the N1 is established for the uppe r but not for the lower limb. We therefore investigated the N1 after p ainful radiant heat stimulation of hand and foot dorsum in 22 subjects . LEPs were recorded from the scalp with midline and temporal electrod es. After hand stimulation N1 was maximal in the contralateral tempora l lead (mean peak latency 156 +/- 23 ms). After foot stimulation N1 wa s maximal in the same lead (200 +/- 22 ms). In the ipsilateral tempora l lead, N1 appeared significantly smaller and later. N2 and P2 were ma ximal in midline electrodes for both stimulus sites. The latency shift between hand and foot stimulation was identical for all three compone nts. These results suggest a contribution of temporo-parietal cortex ( e.g. SII) to the N1 generation for stimulation of upper and lower limb .