THE SCALP TOPOGRAPHIC MAPPING OF HUMAN SOMATOSENSORY EVOKED POTENTIALS
The scalp topographic mappings of somatosensory evoked potential (SEP) to the median and posterior tibial nerve stimulation were recorded from 16 recording electrode locations in 23 normal subjects with MULTI-PURPOSE BIOPHYSICAL DATA PROCESSOR, TOPOGRAPHY-SYSTEM 500 (SAN-EI). Po (P14), the eatliest SEP component to the median nerve stimulation was distributed diffusely with frontal dominancy on the scalp. N1, P1, P2, P3 and N4 were best seen in the contralateral parietal area to the stimulated nerve. N2 and N3 were observed dominantly in the frontal area without significant laterality. The last component, P4 within 200 msec of analysing time had a highly maximum amplitude in the fronto-central region at midline. P1 (P37) component to the posterior tibial nerve stimulation was best seen in the ipsilateral parieto-occipital area to the stimulated nerve in all subjects. The subsequent peaks were observed in the parietal area maximally at midline. The topographic SEP mappings revealed a dynamic and systematic evolution on the scalp in normal individuals, and the diagnostic procedures may expand the clinical utility, especially as regards functional lesions.
