S192 The role of the cerebellum in motion control

Abstract

Objectives To assess the roles of the cerebellum in motion control on the basis of clinical, anatomical, functional imaging and electrophysiological investigations. Methods (a) Review of experimental findings starting from works of pioneers of the 19th century until 2017, (b) assessment of the theory of internal models. Results Anatomically, the cerebellum has a modular organization. Parasagittal bands of Purkinje cells (PCs) project to specific areas of cerebellar nuclei (CN). Functionally, cerebellar cortex (CC) is composed of microzones gathering groups of about 1000 PCs having the same somatotopic receptive field. The intrinsic connectivity networks (ICNs) derived from fMRI studies overlap with maps of structural connectivity. Transsynaptic tracer studies reveal disynaptic pathways linking the cerebellum and basal ganglia. Neurophysiologically, a very robust property of CN is their ability to fire rebound spike bursts following strong hyperpolarization, turning inhibition in CN output spiking. The timing of spiking is critical for the CC and is a pre-requisite for internal models. Anticipation of action is mandatory to plan the sequential movements on the basis of internal/external constraints. Cerebellar dysmetria can now be explained by biased internal models of limb dynamics. Similarly, in Schmahmann’s syndrome a mismatch between reality and perceived reality is suspected. Conclusions The leading theory of forward models is now embracing not only the motor symptoms but also the cognitive deficits observed in cerebellar ataxias. Significance The redundant architecture of the CC makes of the cerebellum an ideal structure to convey signals across microzones in a time-dependent fashion.