ROLE OF AUDITORY CORTEX IN DISCRIMINATION OF CHANGES IN FREQUENCY

Abstract

Cats were trained to avoid shock by responding to small changes in the frequency of a tonal stimulus. After bilateral ablation of auditory areas I, II, and Ep, and after bilateral ablation of somatic area II in addition to AI, AII, and Ep, ability to discriminate changes in frequency was essentially unimpaired. A temporary amnesia for the learned habit occurred but all animals were able to relearn. Postmortem examination of the brains of experimental animals revealed that in all cases of auditory cortex ablation, the anterior 2/3 of the principal part of the medial geniculate was completely degenerated. As the ablation was enlarged to include temporal and insular cortex ventral to the boundaries of the auditory cortex as usually defined, degeneration extended further into the posterior tip of the medial geniculate. In all cases, a small portion of the dorsal posterior tip remained intact. Retrograde degeneration also occurred in the magnocellular division of the medial geniculate and in other thalamic nuclei, such as the pulvinar, lateral geniculate, n. lateralis posterior and n. ventralis posterior. The degeneration outside of the medial geniculate was the result of damage to subcortical pathways or to cortex outside of areas AI, AII, and Ep.