Multiple brain systems generating the rat auditory evoked potential. II. Dissociation of auditory cortex and non-lemniscal generator systems

This study addressed the issue of multiple parallel auditory processing systems and their relationship to the skull-recorded auditory evoked potentials (AEPs) in the unanesthetized, unrestrained rat. In the preceding paper ( Brain Res., 602 (1993) 240–250) it has been shown that auditory cortex activity does not contribute significantly to the vertex maximal AEPs recorded from the dorsal skull of the rat. In the present study, mapping of the AEP skull distribution revealed two sets of components: one set maximal at the dorsal skull vertex, and another set maximal at the lateral skull over auditory cortex. Barbiturate anesthesia eliminated the dorsal skull maximal components (and later components at the lateral skull), but not the early (P7–P11, N15) lateral skull components generated in auditory cortex. Bilateral auditory cortex ablation eliminated the lateral skull maximal AEP components, but not the dorsal skull maximal components. These findings support extensive parallel processing of auditory inputs (reflected by the dorsal AEPs) in the absence of primary auditorycortex. Ablation of primary auditory cortex did result in a modulation of the dorsal skull AEPs, indicative of an interaction between the geniculocortical system and the parallel system which generates the dorsal AEPs.