Hippocampus, context, and conditioning.

Rabbits (Oryctolagus cuniculus) with lesions to either the hippocampus or overlying neocortex and unoperated controls underwent acquisition of the classically conditioned nictitating membrane response to a tone conditioned stimulus and an air puff unconditioned stimulus until they reached a criterion of 8 conditioned responses in any block of 10 trials. They were then returned to their cages. On the next day, they were either placed in the same context in which they underwent initial conditioning or switched to a new context that distinctly differed along olfactory, visual, and tactile dimensions. In relation to unswitched controls, rabbits with lesions to the neocortex and unoperated controls showed a disruption of conditioning when contexts were switched. In contrast, rabbits with lesions to the hippocampus performed at the same levels as unswitched controls. The results are discussed in terms of the possible role of hippocampus in coding context in classical conditioning.