FREQUENCY DISCRIMINATION AFTER BILATERAL ABLATION OF CORTICAL AUDITORY AREAS

Abstract

Cats can relearn an auditory frequency discrimination after bilateral ablation of auditory areas I, II, Ep, SII, and the suprasylvian gyrus and the subsequent degeneration of the medial geniculate body and most of the posterior group of the thalamus. A review of previous work indicates that animals deprived of the thalamocortical auditory system are able to learn frequency discriminations in which the avoidance signal is preceded by a neutral signal whose duration is 1 min. or longer, but are unable to relearn discriminations in which the neutral and avoidance signals are separated by a silent interval or in which the avoidance signal is preceded by a neutral signal which lasts for much less than 1 min. A neural model is proposed to describe the activity of subcortical auditory centers after auditory cortex removal. One distinctive feature of the model is that it assumes that the neural response to a tone will show a decrease in size (habituation) when the tone is repeated once every few seconds for about 1 min. When the neural events which take place during various discriminatory tasks are reconstructed by means of the model, it is found that the frequency discriminations which are severely disrupted by auditory cortex removal and auditory pattern discrimination have a feature in common which distinguishes these tasks from problems not severely disrupted by cortical ablation.