[Analysis of the generators of early cortical somatosensory evoked potentials (N. medianus) using dipole source...

There is still much controversy about the contribution of the brainstem, the thalamus and the somatosensory and motor areas of the various scalp recorded peaks of the somatosensory evoked potentials (SEP) after median nerve stimulation. This study addressed the generator problem of the scalp recorded potentials using brain electric source analysis. In 11 normal subjects median nerve SEPs were recorded from 32 locations. The brain-electric-source-analysis revealed a minimum of 5 sources with overlapping activities in the interval of 12-35 ms post stimulus. The initial deflections were in the time range of the scalp peaks (P14, P18, N20, P22, N30), but there was no single source to fully explain a scalp peak except for the brainstem source of P14. The other sources appeared to reflect activities of the thalamo-cortical-pathway (P18), of the somatosensory areas 3b (N20) and 1 (P22) and of a fifth source (contribution maximal around 30 ms) with no consistent location. The close location of multiple sources makes the precise separation and localisation of the various sources quite difficult in individual data sets.