N20 and P40 somatosensory evoked potentials: thalamic lesions and subcortical origin.

Three patients with well-defined clinical and radiographic lesions have been studied with somatosensory evoked potentials (SSEPs). The data indicate that the primary scalp potentials from stimulation of both the arm and leg (N20 and P40) can be lost with thalamic lesions and would be consistent with these potentials being generated in either the thalamus or thalamocortical radiations.