Adaptability of delay eyelid conditioning requires forebrain input to the cerebellum
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The cerebellum is a region of the brain responsible for an organism’s ability to perform precise, coordinated movements. An abundance of research has characterized the anatomy of the cerebellum, and provides the foundation of current theories regarding the circuitry that supports motor learning. Delay eyelid conditioning is a form of motor learning. It is the learned association of a neutral stimulus and the reflexive response of an eyelid closure resulting in a well-timed eyelid closure in anticipation of the reflexive response. Two aspects of this learning are: different-conditioned stimulus savings and savings of timing. Different-CS savings is a rapid re-learning to a new, different neutral stimulus that occurs more quickly than learning to the original stimulus. Savings of timing is a phenomenon in which the timing of a response is preserved from a prior training experience. This dissertation presents evidence that forebrain input to the cerebellum is required for these aspects of delay eyelid conditioning. We trained animals with electrical stimulation as our neutral stimulus and thereby engaged a specific input pathway to the cerebellum, limiting forebrain inputs. In Chapter 2 we implement this technique and eliminate different-CS savings. These data suggest that forebrain input mediates this phenomenon. We then proceeded to investigate if the prefrontal cortex (PFC) is the forebrain region involved in supporting this aspect of delay eyelid conditioning. We administered electrolytic lesions to the PFC of animals and found their ability to express different-CS savings was impaired. Evidence from these two chapters suggests the PFC provides input to the cerebellum necessary for different-CS savings. Finally, in Chapter 4 we examine savings of timing. We again limit forebrain input to the cerebellum and implement electrical stimulation as our neutral training stimulus. With stimulation as the neutral stimulus, animals do not exhibit savings of timing. The data suggest that a forebrain region is necessary to sustain this phenomenon as well. This dissertation provides two lines of evidence strongly supporting forebrain involvement in these modifications of delay eyelid conditioning - savings and savings of timing. These results convey the importance of accommodating forebrain-cerebellum interactions when developing theories of cerebellar function.