Rebound nystagmus in olivocerebellar atrophy: a clinicopathological correlation

Rebound nystagmus was recorded in a patient with cerebellar dysfunction. Neuropathological examination showed degeneration of the inferior olivary nuclei and the cerebellar cortex. The basis pontis and the brainstem tegmentum were spared. Rebound nystagmus is attributed to a smooth eye movement bias that is generated within intact vestibuloocular pathways to oppose gaze-evoked centripetal drift of the eyes. The source of the rebound bias was not visual, because rebound nystagmus normally occurs in darkness, smooth pursuit was paretic, and the olivocerebellar visual relay pathway was degenerated. An extraretinal, efference copy signal of the eye position error must detect the ocular drift and generate the rebound bias. The neuropathological findings indicate that rebound nystagmus can be a sign of involvement confined to the olivocerebellar circuit and that nonvisual signals of eye position are monitored independently of this cerebellar system.