Subcortical correlates of the somatic, auditory and visual vertex activities in man. I. Bipolar EEG responses and electrical stimulation.

Bipolar responses correlated to somatic, auditory and visual vertex activities were studied in different subcortical structures of patients with implanted electrodes used as an electrophysiological procedure for surgical treatment. In addition, we studied the subjective responses of patients to electrical stimulation of subcortical structures where vertex-like activities (VA) were recorded, in order to determine their possible role in somatic, auditory and visual sensations. Typical subcortical VA evoked by somatic, auditory and visual stimuli, were recorded together from a single structure of a non-specific system including: reticulo-, medial dorsal-thalamic, orbito-frontal, limbic and striatal structures. Typical subcortical VA were formed by 4 consecutive components: O, A, B and C correlated to P1, N1, P2 and N2 of the surface VA. Polarity of component A was inverted between reticulo- and medial-thalamic structures while that of component B was inverted between medial thalamic and dorsal thalamic and between fronto-limbic and striatal structures. Typical subcortical VA were absent within specific thalamic nuclei and pathways in presence or absence of short latency responses evoked by specific sensory stimuli. Atypical subcortical VA of 1, 2 and 3 sensory modalities with inconsistent amplitudes, latencies and polarities were recorded from an intermediate zone surrounding and between specific and non-specific structures. Electrical stimulation of the non-specific structures at the reticulo- and medial thalamic levels elicited sensation of falling down and increase tension and tremor of the contralateral hand while no subjective responses were elicited by the stimulation at the dorsal thalamic, fronto-limbic and striatal levels. Stimulation of the specific structures and the intermediate zone elicited somatic, auditory and visual sensations with and without and apparent topographical organization, respectively.