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Structural Foundations of Cerebellar Information Processing

Richard Apps

Dept of Physiology, University Of Bristol , UK

The talk will review recent progress in our understanding of the principles of organization that underlie cerebellar information processing, with an emphasis on the spatial distribution of climbing fibre and mossy fibre inputs to the cerebellar cortex. While it is generally accepted that a key organizational feature of the mammalian cerebellar cortex is a division into a series of longitudinally-oriented zones (that can be defined by their climbing fibre input arising from different parts of the inferior olivary complex), nevertheless, the way mossy fibre afferents map onto this precise arrangement remains ill-defined.

Evidence will be reviewed that in the paravermal cerebellum the organization of mossy fibre inputs is intimately related to the climbing fibre system. For example: 1) Cortical zones that share a common climbing fibre input also receive common mossy fibre input (as well as independent mossy fibre inputs). 2) Climbing fibre and mossy fibre projection patterns can be correlated, at least in part, to the expression of the molecular marker zebrin. 3) A precise topography is present in the projection of the largest source of mossy fibres- the ponto-cerebellar projection- which can be defined in terms of climbing fibre somatotopy. And 4) pairs of Purkinje cells that are functionally coupled by synchronous timing of their climbing fibre responses, can also display synchronous activity in their simple spike discharges. Taken together these findings suggest that a highly organized relationship exists between mossy fibre and climbing fibre inputs to the cerebellar cortex which is likely to have a significant influence on cerebellar throughput.