INFORMATIONAL NEUROMORPHOLOGY OF THE CORT ICO-CEREBELLO-PONTINE-THALAMO-CORTICAL SYSTEM IN PRIMATES (COMPARED WITH THE BASAL GANGLIA SYSTEM)

The present review analyses a motor circuit which, starting from the c erebral cortex goes through the pontine nucleus, granule cells, Purkin je's neurons, the cerebellar nuclei, the motor thalamus, and back to t he cortex. This system is analysed by resorting to informational neuro morphology which deduces particular properties of information processi ng from spatial features observed on neuronal arborisations or sets of arborisations. The main part of the cerebro-cerebellar circuit is fin e grained with relatively small arborisations. Such a fine grain is no t used here for the preservation of a simple somatotopic representatio n, as is the case for sensory systems, but instead for a processing us ing << patchy maps >> which is a known mode of parallel processing. Th ere is a major break of arborisations geometry which is situated in th e cerebellar cortex between the granule and Purkinje cells. The grain cells axons, the parallel fibers, are numerous and almost unbranched w hile the dendritic arborisations of Purkinje's cells are flat, with a large surface and are perpendicular to the parallel fibers which leads to both a cardinal and a reception convergence. This is also observed in the striato-pallidal system. A significant difference between the two systems which are separated almost everywhere, notably at the thal amic relays level, is that the system passing through the cerebellum e ssentially processes sensorimotor information while the basal ganglia system receives information from almost the whole cortex. The return t o the cortical targets causes complex interferences. It clearly appear s that the two motor systems process information in different manners.