Olivocerebellar orchestration of learning-dependent timing

Over the past decades, theories about cerebellar learning have evolved. A relatively simple view that highlighted the contribution of one major form of heterosynaptic plasticity to cerebellar motor learning has given way to a plethora of perspectives that suggest that many different forms of synaptic and non-synaptic plasticity, acting at various sites, can control multiple types of learning behaviour including cognitive processes. The challenge is to reconcile these different mechanisms and unite them into a single overall concept. In this lecture I review our current understanding of the changes in the activity of cerebellar Purkinje cells in different ‘microzones’ during various forms of learning-dependent timing. During the initial stages of relatively simple forms of learning, such as modification of sensorimotor reflexes, the simple spike activity of each microzone is bound to either increase or decrease, dependent on the timing of the climbing fiber input originating from the inferior olive. Instead, during more complex forms of learning, including planning and decision making, mixed sequences of increases and decreases of activity can co-occur in different microzones, operating as ensembles in synergy. In either case, the upbound and downbound changes in activity in the microzones appear to depend on the directional and temporal demands of the downstream circuitry involved, continuously finetuning and orchestrating the optimal behaviour.