Microelectrode recordings of multiple-unit activity were made from the dorsal cap of the inferior olive of anesthetized and unanesthetized rabbits during vestibular and optokinetic stimulation. A large field potential could be evoked in the dorsal cap by photic stimulation of the contralateral eye when the rabbit was anesthetized with sodium pentobarbital or chloralose-urethan. This field potential could not be evoked in rabbits that were anesthetized with halothane or in unanesthetized rabbits. Dorsal cap neurons were maximally excited by large, contrast-rich stimuli in the posterior anterior direction at a velocity of 1-2°/s. The discharge rate of dorsal cap neurons was decreased by stimuli moving in the opposite direction. The activity of dorsal cap neurons was not modulated by vestibular stimulation when visual inputs were excluded. Dorsal cap neurons were sensitive to retinal slip velocity and higher derivatives of optokinetic stimulation. Their activity was related to eye movements only when the eye movements affected movement of optokinetic images on the retina.
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