Cerebellum cerebellum may be absent. The inherited neurological disorders Machado–Joseph disease, ataxia telangiectasia, and Friedreich's ataxia cause progressive neurodegeneration linked to cerebellar loss. Congenital brain malformations outside the cerebellum can, in turn, cause herniation of cerebellar tissue, as seen in some forms of Arnold–Chiari malformation. Other conditions that are closely linked to cerebellar degeneration include the idiopathic progressive neurological disorders multiple system atrophy and Ramsay Hunt syndrome type I, and the autoimmune disorder paraneoplastic cerebellar degeneration, in which tumors elsewhere in the body elicit an autoimmune response that causes neuronal loss in the cerebellum. Cerebellar atrophy can result from an acute
Anatomy of the cerebellum cerebellar cortex. Under resting conditions in animal experiments, groups of olivary neurons discharge synchronously at 5 to 10 Hz (impulses/s). In the cerebellar cortex, the response of Purkinje cells takes the form of complex spikes. The cerebellum send its projections back to the cerebral cortex via the Cerebellothalamic tract. The cerebellar lateral expansion, or the neocerebellum, may be associated with cognitive functions, and it is anatomically linked with the lateral prefrontal cortex. It shows greatest activity during speech, with a one-sided predominance consistent with a possible linkage (via the thalamus) with the motor speech area. When lesions occur in the