Neuronal responses of the rabbit cerebellum during acquisition and performance of a classically conditioned nictitating membrane-eyelid response.

Neuronal activity was recorded from regions of the cerebellar cortex and dentate-interpositus nuclei during learning and/or performance of a classically conditioned nictitating membrane (NM-a third eyelid)/eyeblink response in the rabbit. It was found that neurons located within restricted portions of the ansiform lobule and anterior lobe cortical regions and of the dentate-interpositus nuclei respond in relation to the performance of the learned eyeblink response. Furthermore, chronic recordings from the dentate-interpositus nuclei revealed that these responses develop in close relation to the learning of the conditioned eyeblink response. Stimulation of the dentate-interpositus nuclei through the recording electrodes in some cases yielded eyelid closure and NM extension in both trained and untrained animals. Lesion of the axons of the dentate-interpositus nuclei (superior cerebellar peduncle), a manipulation which is known to abolish the learned eyeblink response, abolished the stimulation effect. We have previously reported that lesions of the dentate-interpositus nuclei cause abolition of the learned eyeblink response. In the present study, we report that lesions of the regions of cerebellar cortex projecting to the dentate-interpositus nuclei do not permanently abolish the conditioned response, although the amplitude-time course of the learned response could be affected. These results, together with results of other studies, demonstrate that the medial dentate and/or lateral interpositus nuclei are active during learning and performance of the conditioned eyeblink response, are capable of producing this learned response, and are essential for the learning and retention of the conditioned eyeblink response. Therefore, the medial dentate and/or lateral interpositus nuclei are a part of the essential neuronal circuit involved in the learning and production of the classically conditioned eyeblink response in the rabbit.