Vestibular nerve activity in the alert monkey during vestibular and optokinetic nystagmus.

Activity of vestibular nerve fibers and eye movements were recorded in the alert monkey during natural stimulation. The animal was rotated about a vertical axis in the dark with velocity trapezoids (vestibular), or a striped cylinder was rotated around the stationary monkey ()optokinetic), or these stimuli were combined. After velocity steps in the dark, neuronal activity declined with a dominant time constant of 5-6 s. The time constant of nystagmus recorded simultaneously was always longer, on average 23 s. Vestibular nerve activity was not influenced by optokinetic patterns or additional visual stimuli during combined visual-vestibular stimulation. Thus, in contrast to vestibular nuclei neurons, vestibular nerve activity in the alert monkey is only determined by head acceleration and cannot be related to the nystagmus response or visual stimuli.