Discrete lesions of the cerebellar cortex abolish the classically conditioned nictitating membrane response of the rabbit.

The classically conditioned nictitating membrane response (NMR) of the rabbit is useful for analyses of brain structures and pathways involved in mammalian associative learning. Lesions of the entire cerebellum, its nuclei or its efferent pathway abolish conditioned NMR learning and prevent its reacquisition. Until now it has not been clear whether the cerebellar cortex is an essential part of the circuitry for NMR conditioning. Here we report that small lesions of the cerebellar cortex in the hemispheral portion of lobule VI, with sparing of the underlying nuclei, abolish the ipsilateral conditioned NMR and prevent it from being reacquired.