Cerebellar Control of the Vestibulo-Ocular Reflex--Around the Flocculus Hypothesis

The vestibulo-ocular reflex (VOR) is an elementary reflex, which attracted the attention of a number of classical neurophysiologists who studied, in particular, the reflexive compensatory eye movements induced by head movements (cfMagnus 1924, Lorente de No 1931). The major pathway for this reflex is the well-defined trineuronal are, composed of primary vestibu­ lar neurons, secondary vestibular neurons, and oculomotor neurons (Ra­ mon y Cajal 1909, Lorente de N6 1931, 1933, Szentagothai 1943, 1950, 1964, Brodal & Pompeiano 1957). The pioneering electrophysiological work by Lorente de N6 (1939) and by subsequent investigators recognized that the vestibulo-ocular reflex involves both excitation and inhibition (Szentllgothai 1950, Cohen et al 1964). More recent data about the VOR have been reviewed by Brodal (1974), Cohen (1974), Precht (1978), and Wilson & Melvill Jones (1979). In recent years, the vestibulo-ocular refiex has been reexamined in detail because of its close relationship with the cerebellum. Supported by remark­ able advances in cerebellar physiology and eye movement studies, the VOR has become an interesting and important subject of neurophysiology, espe­ cially for investigation of cerebellar control mechanisms. This article re­ views the efforts made in the past decade toward understanding the