Effects of bilateral auditory cortex ablation on behavior and unit activity in rat inferior colliculus during differential conditioning

Abstract

The development of both behavioral responses and short-latency responses of inferior colliculus neurons to tone pips was studied in normal rats and rats with bilateral ablation of auditory cortex during a differential conditioning experiment. Behavior measured was the development of a differential movement during the 1 s interval between the onset of the tone CS+ [positive conditioned stimulus] and the food pellet US [unconditioned stimulus]. Some animals with small lesions developed this behavior, but no animal with large lesions did so. Unit responses during the period 5-11 ms after stimulus onset were measured before and during conditioning. A large effect of the lesions on the variability of the background firing rates of neurons during conditioning but not during pseudoconditioning was discussed. In normal animals an approximately equal number of units showed background increases and decreases during conditioning. In the lesioned animals there were more background increases and almost no background decreases during conditioning. The idea that during the learning of such a discrimination, a nonspecific activation from noncortical structures is selectively antagonized by cortical efferents was presented.