Cross -modal savings of the classically conditioned eyeblink response

Over the past century classical conditioning procedures have been widely used to determine numerous behavioral and neurobiological components underlying associative learning. The experiments in this thesis used eyeblink classical conditioning procedures to investigate a form of associative memory called cross-modal savings. Cross-modal savings occurs when a conditioned stimulus (CS) from one sensory modality (e.g., an auditory CS) is greatly enhanced when the subject has been previously trained with a CS from a different sensory modality (e.g., a visual CS). Enhanced acquisition to the new modality CS is evidence that associative memories can generalize across different sensory modalities. Previous experiments have investigated some of the behavioral mechanics of cross-modal savings in eyeblink conditioning, but what has been lacking is an understanding about the neurobiological substrates that support this type of learning. The experiments in this thesis were, therefore, designed to identify some of these neurobiological components. Temporary brain inactivation and single-unit neuronal recording techniques were used to examine the role of the cerebellum and pontine nucleus for establishing cross modal savings in eyeblink conditioning with rats. The first experiment demonstrated that rats show substantial savings during transfer training from one modality CS to a different modality CS. The second experiment found that cerebellar inactivation during initial acquisition to the first modality CS completely prevented savings when training was switched to the second modality CS. The third experiment showed that cerebellar inactivation during cross modal training also prevented learning the second modality CS. The fourth experiment revealed that a mechanism of cross-modal savings involves multimodal processing in individual neurons in the cerebellar interpositus nucleus (IPN) during cross-modal transfer. The fourth experiment also showed a mechanism of cross-modal savings involves multisensory integration in the pontine nucleus (PN) which relays CS information to the cerebellum. It is possible feedback from the IPN to the PN is a mechanism for the enhancement of learning with the cross-modal CS.