Developments in the Marr-Albus-Ito hypothesis: a review of the role of the cerebellum in error processing

The cerebellum is a complex part of the brain that plays a role in co-ordination, motor learning and error processing. The ‘Marr-Albus-Ito hypothesis’ provides a description of how different types of neurons within the cerebellum interact to facilitate motor learning. In the classical model, climbing fibres from the inferior olive influence Purkinje cells to produce complex spikes. These signals modulate interactions between Purkinje cells and parallel fibres, contributing to error processing and increasing sensitivity of reflexes such as the vestibulo-occular reflex (VOR). Certain cerebellar functions, such as down regulation of reflex sensitivity, were not fully explained by the classical model. New insights have contributed to our understanding of the structure and function of the cerebellum. For example, when acted upon only by parallel fibres, Purkinje cells create simple spikes that allow for decreasing sensitivity of the VOR. Simple spikes also play a role in error processing through facilitating prediction of movement within the cerebellum. Further developments, such as uncovering additional sites of neuroconnection between Purkinje cells and vestibular nuclei, have contributed to our understanding of how the cerebellum influences ocular reflexes. Finally, we have also accumulated evidence that the cerebellum not only processes motor errors, but also functions to refine mental models held within the temporo-parietal cortex. This article reviews how recent developments have added to the Mar-Albus-Ito hypothesis to provide a more complete understanding of the inner workings of the cerebellum