HUMAN SHORT-LATENCY CORTICAL RESPONSES TO SOMATOSENSORY STIMULATION -A HIGH-RESOLUTION EEG STUDY

HUMAN short-latency cortical responses to median nerve stimulation wer e investigated with a new high resolution electroencephalography techn ology that markedly enhanced spatial details of somatosensory-evoked p otentials (SEPs). Maximum amplitude potentials were estimated over con tralateral and/or frontal-mesial scalp regions about 20, 22, 24, 26, 3 0, 32 and 45 ms following the stimulation. Frontal-lateral P20-N24-N30 -P45 and parietal-lateral N20-P24-P30-N45 showed dipolar patterns, whe reas frontal-mesial N24-N30-P45 and central-lateral P22-N26-N32-P45 pr esented no clearcut dipole counterpart. Plausibly, the spatially enhan ced frontal-parietal SEP components were generated (tangential dipoles ) within the lateral central sulcus cortex, and anticipated the centra l-lateral and frontal-mesial components generated (radial dipoles) fro m the crown of the pre- and/or post-central gyri and the supplementary motor area, respectively.