Cerebellum and oculomotor defi cits

The cerebellum is a key structure within a widely distributed neural network that controls movements including those of the eyes. Both the immediate, on-line control of movement and more long-term adaptive functions are within the purview of the cerebellum. Ocular motor abnormalities are prominent in patients with cerebellar disorders and aid clinical anatomical localization. Assigning specifi c functions to structures within the cerebellum, however, is more problematic. For example, each of the ocular motor subsystems-saccades, pursuit, vestibular, and vergence-has multiple representations in different parts of the cerebellum, and a functional distinction is not always possible. Furthermore, the cerebellum is so richly interconnected with other parts of the brain that understanding its function depends on considering the entire motor control circuit within which it resides. There are three major structural units in the cerebellum associated with control of eye movements: (1) the fl occulus and parafl occulus (tonsil), (2) nodulus and uvula, and (3) the dorsal vermis (lobules VI-VII) and underlying fastigial nuclei. Here we review the main ocular motor defi cits associated with cerebellar lesions and infer function accordingly.