Links from complex spikes to local plasticity and motor learning in the cerebellum of awake-behaving monkeys

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Abstract
This study presents a trial-by-trial analysis of responses of Purkinje cells of the cerebellum in awake-behaving monkeys as they carry out a simple motor learning task. The results show that the presence of a complex spike on one learning trial is linked to a depression of simple-spike responses on a subsequent trial when behavioral learning takes place. The hypothesis of cerebellar learning proposes that complex spikes in Purkinje cells engage mechanisms of plasticity in the cerebellar cortex; in turn, changes in the cerebellum depress the simple-spike response of Purkinje cells to a given stimulus and cause the adaptive modification of a motor behavior. Many elements of this hypothesis have been supported by prior experiments, and correlations have been found between complex spikes, simple-spike plasticity and behavior during the learning process. We carried out a trial-by-trial analysis of Purkinje cell responses in awake-behaving monkeys and found evidence for a causal role for complex spikes in the induction of cerebellar plasticity during a simple motor learning task. We found that the presence of a complex spike on one learning trial was linked to a substantial depression of simple-spike responses on the subsequent trial, at a time when behavioral learning was expressed.