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The cerebellum is a cauliflower-shaped section of the brain. It forms the hindbrain, at the bottom rear of the head, directly behind the pons.

Two main theories address the function of the cerebellum. One claims that the cerebellum functions as a regulator of the timing of movements. This has emerged from studies of patients whose timed movements are disrupted. The other claims that the cerebellum operates as a learning machine, encoding information like a computer. This was first proposed by Marr and Albus in the early 1970's. Like many controversies in biology, some of both of these claims is true. Studies of motor learning in the vestibulo-ocular reflex and eyeblink conditioning are demonstrating that timing and amplitude of learned movements are encoded by the cerebellum. A recent review article (2004) explores how different mechanisms of the cerebellum may contribute to learning and other behaviors.

What is clear, from human patient studies and from animal behavioral studies, is that the cerebellum is a complex system mostly dedicated to the intricacies of voluntary movement, including managing walking and balance. Damage to the cerebellum leaves the sufferer with a gait that appears drunken and is difficult to control. Some modern fMRI studies show that the cerebellum is important for attention, reading, perception of time, and may be impaired in dyslexia, Alzheimer's disease, and other neurological disorders.

A tree-like internal structure has led to the region being described as the arbor vitea or tree of life. Afferent and efferent nerve traffic of the cerrebellum passes through the trunk-like cerebellar vermis.

The embryonic cerebellum develops from the superior dorsal aspect of the rhombencephalon. In the mature mammallian brain, the cerebellum comprises a distinct structure at the back of the brain. The cerebellum is of archipalliar phylogenetic origin, shared as a prototypical brain structure by animals from the most elementary to the most advanced.

Many synaptic plasticity mechanisms have been found throughout the cerebellum. The Marr-Albus model mostly attributes motor learning to a single plasticity mechanism, long-term depression of parallel fiber synapses.

See also