MESODIENCEPHALIC AND CEREBELLAR INFLUENCES ON OPTOKINETIC AND VESTIBULAR NYSTAGMUS.

Fourteen cats were implanted with chronic electrodes in the mesodiencephalon and fastigial nuclei of the cerebellum. Concomitant electrical stimulation of the mesodiencephalon during optokinetic OKN or vestibular stimulation caused an increase in frequency of the nystagmic response when the stimulus was applied contralateral to the direction of the fast phase of nystagmus ipsilateral stimulation caused a decrement in frequency. Electrical stimulation of the fastigial nuclei during OKN or vestibular stimulation led to a complete inhibition of the nystagmus independent of the side stimulated and a centering of the eyes. Data suggest that the cerebellar roof nuclei may be involved with mediating the responses necessary for inhibition of nystagmus through visual fixation. Author