The response of 8th nerve fibers to horizontal sinusoidal oscillation in the alert monkey.

1. The activity of single units in the vestibular nerve was recorded in alert monkeys in stationary positions and during horizontal sinusoidal angular rotations at frequencies from 0.10 to 4.0 Hz. 2. All units encountered had a spontaneous discharge rate which varied from 48.61 to 178.25 spikes/sec. The regularity of firing for each unit also varied. 3. To ipsilateral rotation of the animal the units responded with an increase in firing rate. Rotations in the opposite direction decreased the firing rate relative to the spontaneous discharge rate. The unit response was indicative of imposed velocity rather than acceleration or position. The harmonic distortion of the unit response was not a function of frequency of oscillation. For 43 units at 0.78 Hz the harmonic distortion averaged 23.9%. 4. There was some correlation between the regularity of spontaneous discharge of each unit and the degree of diminished phase lag at higher frequencies of oscillation. Those units with the most irregular spontaneous discharge patterns were most likely to exhibit a diminishing phase lag re:acceleration as frequency of oscillation increased beyond 0.5 Hz. 5. No unit activity related to eye movements was encountered in the vestibular nerve.