Vestibulo-ocular reflexThe vestibulo-ocular reflex, or VOR, is a reflex eye movement that stabilizes images on the retina during head movement by producing an eye movement in the direction opposite to head movement. If the VOR is poorly calibrated, then head movements result in image motion on the retina, resulting in blurred vision. Under such conditions, motor learning adjusts the gain of the VOR to produce more accurate eye motion. Such adjustments are needed throughout life, as neurons and muscles develop, weaken, and die--or for humans, when a new pair of eyeglasses changes the magnification of the visual field. The main neural circuit for the VOR is simple. Vestibular nuclei in the brainstem receive signals related to head movement from the vestibular nerve and project to oculomotor nuclei, which contain motoneurons that drive eye muscle activity. The flocculus and ventral paraflocculus of the cerebellum form an inhibitory side loop in the VOR circuit. Mossy fibers provide vestibular input to the cerebellum, and Purkinje cells inhibit VOR interneurons in the vestibular nucleus. For the VOR, the vestibular nuclei serve the role that the deep cerebellar nuclei serve for other cerebellum-dependent behaviors like eyeblink conditioning. Thus, when we refer to the contribution of the cerebellum to the VOR, we mean the cerebellar cortex. External links
Categories: Reflexes |
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