Rahman, Shbana; (2001) The cerebellar cortex and motor learning. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The role of the cerebellum in movement control may involve the formation and storage of motor memories. This thesis examines the role of the cerebellum in a simple associative motor learning task - classical conditioning of the nictitating membrane response (NMR) of the rabbit. Repeated pairings of a tone stimulus with a tactile periocular stimulus leads to the formation of conditioned NMRs. Lesion studies have shown that conditioning of the eyelid response and NMR is critically dependent upon the cerebellum and its associated circuitry. However, permanent lesions cannot establish whether memories are stored in the cerebellum because they cannot dissociate performance and learning effects. Localised reversible inactivations can reveal whether a region is actively involved in learning and the formation of memories because the system can be tested after recovery from the inactivation. The inferior olive, cerebellar cortex and cerebellar nuclei are interconnected to form a module whose function can be altered by disturbances at any point in the circuit. Reversible inactivations of the cerebellar anterior interpositus nucleus or the olivary inputs to the cerebellum prevent NMR conditioning, but inactivation of cerebellar nuclear efferents in the brachium conjunctivum does not. These findings provide strong support for the suggestion that essential plasticity for NMR conditioning is within the cerebellum. However, reversible inactivations have not been used directly to test whether cerebellar cortical function is also critical for learning. The experiments presented in this thesis used reversible inactivations of cerebellar cortical lobule HVI to demonstrate that it is essential for performance, acquisition and extinction of NMR conditioning. These findings are consistent with several theoretical models of motor learning that assign essential plasticity to the cerebellar cortex. The results are discussed in the light of our current understanding of cerebellar cortical plasticity at the system and cellular level.

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