Relative Contributions of the Cerebellar Cortex and Cerebellar Nucleus to Eyelid Conditioning

We have presented data addressing the relative contributions of the cerebellar cortex and nuclei in the acquisition and expression of conditioned eyelid responses. Data from a series of studies support the notion that while plasticity occurs in both the cerebellar cortex and nucleus, the cerebellar cortex is essential for acquisition, extinction, and for the proper expression of conditioned eyelid responses. We have presented arguments that the experiments that support this position were designed in ways to preclude confounds that were present in other attempts to identify the role of the cerebellar cortex in eyelid conditioning. We have also presented evidence that suggests plasticity in both the cerebellar cortex and nucleus is required for the expression of a conditioned response, and that reversing this plasticity only in the cerebellar cortex may be sufficient to produce extinction of conditioned responses. Computer simulations based on the connectivity of the cerebellum and on the sites and rules for plasticity suggested by our studies are able to acquire properly timed conditioned responses, and to extinguish responses with CS-alone presentations. These simulations will provide many empirically testable predictions that should facilitate our understanding of the cerebellar mechanisms of eyelid conditioning.