Functional organization of the intermediate cerebellum.

The uniform organisation of the neuronal circuitry throughout the cerebellar cortex suggests a uniform mode of operation and thus emphasises the importance of local afferent and efferent connections in determining the function of a particular part of the cortex. Based on the organisation of these connections the cerebellar cortex of the cat is divided into about ten sagittally oriented zones (see Ito, 1984 for references). A zone is anatomically defined by its projection to a restricted part of the intracerebellar or vestibular nuclei and its climbing fibre input from a circumscribed part of the inferior olive. Some of the zones are functionally coupled in that they receive branching collaterals from common olivary neurones and in turn project to the same subdivision of the intracerebellar nuclei. Since each part of the inferior olive receives input from a specific set of spino-olivary pathways, the zones can be electrophysiologically identified by the latencies and receptive fields of climbing fibre responses evoked on peripheral stimulation. The organisation of olivary afferent and nuclear efferent connections suggests that each zone, or in some cases an ensemble of zones, controls specific motor systems.