Intracranial studies on potential generators of some vertex auditory evoked potentials in man.

Potential generators for surface brain stem (ABSP), P200 and P300 auditory evoked potentials have been localized in patients with implanted electrodes used as an electrophysiological procedure for surgical treatment. Results suggest that surface SP and SN1-2 and components V, VI and VII of ABSP and component P3 and P300 result from specific auditory system activation, while components N1-P2 of P200 and N2-N4 of P300 result from nonspecific systems. Two subcortical generators were localized related to surface ABSP-one at the medial geniculate thalamic region (MG) related to SP and SN1 and V, VI, VII potentials, the other near the hippocampal region related to SN2. One subcortical generator related to surface N1-P2 of P200 was found near the caudal mesencephalic reticular formation, and the other two subcortical generators related to surface N2-P4 and P3 of P300 were found at the subthalamic and MG regions, respectively. Reverse polarity of some bipolar responses and lack of amplitude-latency gradients of some referential potentials at the gyrus orbitalis, rostral thalamus and anterior commissure, suggest the existence of other additional potential generators more rostrally located.