Human short latency cortical responses to somatosensory stimulation. A high resolution EEG study.

Human short-latency cortical responses to median nerve stimulation were investigated with a new high resolution electroencephalography technology that markedly enhanced spatial details of somatosensory-evoked potentials (SEPs). Maximum amplitude potentials were estimated over contralateral and/or frontal-mesial scalp regions about 20, 22, 24, 26, 30, 32 and 45 ms following the stimulation. Frontal-lateral P20-N24-N30-P45 and parietal-lateral N20-P24-P30-N45 showed dipolar patterns, whereas frontal-mesial N24-N30-P45 and central-lateral P22-N26-N32-P45 presented no clearcut dipole counterpart. Plausibly, the spatially enhanced frontal-parietal SEP components were generated (tangential dipoles) within the lateral central sulcus cortex, and anticipated the central-lateral and frontal-mesial components generated (radial dipoles) from the crown of the pre- and/or post-central gyri and the supplementary motor area, respectively.