The largest structure of the HINDBRAIN, involved in MOTOR CONTROL and LEARNING. Although its simple neuronal circuitry has made it a popular target of anatomists, neurologists such as Gordon Holmes (1876–1966) have emphasized the motor deficits which follow from cerebellar damage. Holmes described three main signs of cerebellar disease: changes in muscular tone, postural difficulties (see POSTURE) and INTENTION TREMOR Studies of the cerebellum have therefore focused largely on motor coordination and learning. More recently, there has been a revival of interest in the idea that the cerebellum contributes to some higher-level functions such as LANGUAGE and MEMORY. The cerebellum is typically subdivided into three divisions or lobes. The phylogenetically ‘oldest’ of these is the FLOCCULONODULAR LOBE (the ‘ARCHICEREBELLUM’), largely related to vestibular functions. The anterior lobe (the PALAEOCEREBELLUM) is typically associated with position sense. Damage to these two lobes results in abnormalities in GAIT and decreased muscular tone. The NEOCEREBELLUM (largely synonymous with the posterior lobe) is greatly expanded in species with substantial extents of cerebral cortex. Damage in this lobe can results in ab-normal reaching movements, intention tremor, and so on.
The cerebellum receives its inputs via two major systems: the CLIMBING FIBRES and the MOSSY FIBRES. The mossy fibre system is largely concerned with conveying visual information from extrastriate visual cortices and the SUPERIOR COLLICULUS to the ccrebellum. The climbing fibre system carries infomation from many sensory systems, not just vision, and its visual inputs are largely from the pretectal area and the accessory optic system. Some theorists believe that the climbing fibre system detects unexpected sensory stimuli which are not a consequence of the subject’s own movements, and as a consequence can serve as ‘error detectors’, important for recalibration of many sensorimotor systems. The uniformity of cerebellar circuitry implies that similar operations are performed for a number of different sensorimotor activities, including error correction in pursuit eye movements, the vestibulo-ocular reflex, and visually guided limb movements. The cerebellum does not control movements directly; instead it seems to play some sort of regulatory role by inhibiting and disinhibiting motor networks in MOTOR CORTEX, BRAINSTEM premotor networks and the SPINAL CORD. The neocerebellum is massively expanded in man. Given the large connections with many regions of neocortex, some theorists now argue for language and cognitive functions of the cerebellum. Although an attractive hypothesis from the point of view of a physiological psychologist, the evidence for cognitive functions of the cerebellum remains controversial.
