Vestibular nuclei activity in the alert monkey during suppression of vestibular and optokinetic nystagmus.

Single neurons were recorded in the vestibular nuclei of monkeys trained to suppress nystagmus by visual fixation during vestibular or optokinetic stimulation. During optokinetic nystagmus vestibular nuclei neurons exhibit frequency changes. With the suppression of optokinetic nystagmus this neuronal activity on average is attenuated by 40% at stimulus velocities of 40 degrees/s. At a stimulus velocity of 5 degrees/s responses are, under both conditions, close to threshold. For steps in velocity, suppression of vestibular nystagmus shortens the time constants of the decay of neuronal activity from 15--35 s to 5--9 s, while the amplitude of the response remains unchanged. The results are discussed in relation to current models of visual-vestibular interaction. These models use a feedback mechanism which normally operates during vestibular and optokinetic nystagmus. Nystagmus suppression interrupts this feedback loop.