Pavlovian conditioning and extinction of context cues and punctate CSs in rats with ibotenate lesions of the hippocampus

Abstract

The degree to which conditioned stimuli (CSs) control responding is often influenced when contextual cues are also associated with the unconditioned stimulus (US). In Experiment 1, selective ibotenate (IBO) lesions of the hippocampus impaired the ability of rats to inhibit responding to contextual cues made excitatory by presentation of unsignaled USs during simple Pavlovian CS—US training. Hippocampal damage had little effect on responding if few or no unsignaled USs had been delivered in the context. In Experiment 2, there was no evidence of increased responding to contextual cues when IBO lesions were given after excitatory training. However, lesioned rats showed greater resistance to CS extinction than did controls. An interpretation that encompasses these and other findings is that selective lesions of the hippocampus impair the formation of at least some types of inhibitory associations.