Hemispheric asymmetries of early cortical somatosensory evoked potentials revealed by topographic analysis.

Scalp topography of the early cortical SEPs was analysed in 50 normal right handed subjects. The following hemispheric asymmetries of the potentials were found: 1) The maximal amplitude of N20 was located predominantly at the P electrode after right sided stimulation, but varied between the CP, P and O electrode after left sided stimulation. 2) The N20 amplitudes were higher after right sided stimulation in approximately 70% of the subjects and the P25 and N30 amplitudes were higher after left sided stimulation in again approximately 70% of the subjects. No side difference of amplitudes was found for the subcortical N14. The N20 amplitude and location asymmetries were attributed to an anatomical asymmetry of the somatosensory cortex.