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Learning-Dependent Plasticity in Cerebellar Deep Nucleus During Eyelid Conditioning

Michael Mauk

University of Texas Health Science Center at Houston Medical School , Dept of Neurobiology and Anatomy , Texas , USA

Everyone in this group is aware of the many ideas about learning-related plasticity in cerebellar cortex during motor learning. Most may be equally aware of debates over the years about relative contributions of plasticity in cerebellar cortex versus plasticity in cerebellar deep nucleus, in particular to examples of learning such as eyelid conditioning and VOR adaptation. Early on, we have been swayed by evidence consistent with the notion that plasticity in both cortex and deep nucleus occurs during these examples of learning. We have also produced ideas how the relative contributions of these forms of plasticity may vary depending on various circumstances. The central observation guiding this thinking relates to the effects of removing or inactivating the contribution of cerebellar cortex on the expression of already learned conditioned responses. This is, as many will know, a strongly debated topic. In our hands, the effect of removing the contribution of the cerebellar cortex has not been abolition of conditioned responses, but rather, the disruption of their learned timing. Pre lesion responses are time to peak appropriately just before the presentation of the US . Post-lesion responses show much shorter and relatively fixed latencies to onset. We have argued since 1993 that these short latency responses reflect learning related plasticity outside the cerebellar cortex, possibly in deep cerebellar nucleus. I will present results from stimulation and reversible inactivation studies that demonstrate these short-latency responses are associative and are mediated by plasticity in deep cerebellar nucleus. I will also review older work showing that this plasticity contributes to savings – relearning is faster than original learning. Time permitting, I will also present newer data suggesting the existence of a short-term form of cerebellar plasticity in cerebellar cortex during eyelid conditioning.