Frequency-specific cellular changes in the auditory system during acquisition and reversal of discriminative conditioning

Abstract

The possibility that learning induces frequency-specific changes at different levels of the auditory system was investigated by recording multiunit activity at the level of the auditory cortex, the magnocellular medial geniculate, and the dorsal cochlear nucleus. Chronically implanted rats were submitted to frequency discrimination (CS+/CS-) and reversal training while they were engaged in a leverpressing for food task. The conditioned suppression response indicated the acquisition of the discrimination and its reversal at the behavioral level. Off-line test sessions, during which different frequencies were tested, were conducted before conditioning, after acquisition of the initial discrimination, and after its reversal. They showed that frequency-specific changes occurred during the initial discrimination at the level of the auditory cortex, the medial geniculate, and, to a lesser extent, the dorsal cochlear nucleus. After acquisition of the reversal, frequency-specific changes, in relation to the new reinforcement rule, were also detected at the cortical and thalamic level but not at the cochlear nucleus level. These results indicate that frequency-specific changes can occur during conditioning at different levels of the CS auditory pathway and suggest that interactions between these different levels must be studied to understand modifications of information processing during learning.