Classical Conditioning of Eyeblink in Decerebrate Cats and Ferrets

Summary

Several lines of evidence suggest that the cerebellum is involved in classical conditioning of the eyeblink response. For instance, lesions to the interpositus nucleus abolish both learning and retention of conditioned responses. There is strong disagreement about the precise nature of the cerebellar involvement, however. Although many now believe that it is the site of learning, is has also been argued that the cerebellum is merely necessary for the normal performance of conditioned responses. In order to clarify the role of the cerebellum in conditioning, electrophysiological techniques were applied to decerebrate cats and ferrets, which can acquire normal conditioned responses. Four small discrete areas of the cerebellar cortex have been identified which seem to control the orbicularis oculi muscle. Electrical stimulation of these areas, which inhibits neurones in the interpositus nucleus, completely suppresses a conditioned response but has only a weak effect on the unconditioned response. Recordings from Purkinje cells in one of these areas show firing patterns which are consistent with their being involved in the learning of the conditioned response. In combination with results from other groups, these findings provide strong support for the cerebellar learning hypothesis.