Dipole modelling of median nerve SEPs in normal subjects and patients with small subcortical infarcts.

Somatosensory evoked potentials (SEPs) to median nerve stimulation were analyzed by means of spatio-temporal dipole modelling in 6 normal subjects and 8 patients with small infarcts in the thalamo-cortical radiation or thalamus. The SEPs could be modelled by a tangentially and a radially oriented equivalent dipole in the region of the contralateral cortical hand area and an equivalent dipole located in the region of the brain-stem. In 3 patients with absence or reduction of amplitudes of cortically generated SEP components, the activity of both cortical dipoles was lost or reduced. In 2 patients the frontally recorded SEP component P20 was lost; in one of them the activity of mainly the tangential dipole was reduced.