[Informational neuro-morphology of the cortico-ponto-cerebello-thalamo-cortical system in primates (compared with basal ganglia system)].

The present review analyses a motor circuit which, starting from the cerebral cortex goes through the pontine nucleus, granule cells, Purkinje's neurons, the cerebellar nuclei, the motor thalamus, and back to the cortex. This system is analysed by resorting to informational neuromorphology which deduces particular properties of information processing from spatial features observed on neuronal arborisations or sets of arborisations. The main part of the cerebro-cerebellar circuit is fine grained with relatively small arborisations. Such a fine grain is not used here for the preservation of a simple somatotopic representation, as is the case for sensory systems, but instead for a processing using "patchy maps" which is a known mode of parallel processing. There is a major break of arborisations geometry which is situated in the cerebellar cortex between the granule and Purkinje cells. The grain cells axons, the parallel fibers, are numerous and almost unbranched while 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 thalamic relays level, is that the system passing through the cerebellum essentially processes sensorimotor information while the basal ganglia system receives information from almost the whole cortex. The return to the cortical targets causes complex interferences. It clearly appears that the two motor systems process information in different manners.