Contribution of oculomotor signals to the behavior of rabbit floccular Purkinje cells during reflex eye movements

Abstract

Alert pigmented rabbits were stimulated in 3 ways: (1) weak repetitive electrical stimulation (10–30 Hz) of an optic tract which induced nystagmic and after-nystagmic eye movements; (2) sinusoidal whole-body oscillation (5° peak-to-peak, 0.1 Hz) which induced the horizontal vestibulo-ocular reflex (HVOR); (3) sinusoidal oscillation (2.5°, 0.33 Hz) of a screen with a dot pattern which drove the horizontal optokinetic eye movement response (HOKR). Single units were recorded from Purkinje cells in the floccular H-zone where local stimulation caused a horizontal shift of the eyes. During slow phases of optic-tract-induced nystagmus and after-nystagmus, most of the H-zone Purkinje cells tested exhibited changes in discharges of simple spikes, an increase at a mean rate of 1.74 for ipsilaterally directed and 1.17 [spikes/s]/[deg/s] for contralaterally directed eye velocity. One-third of the H-zone Purkinje cells changed simple spike discharges depending on the eye position. During HVOR, most of the H-zone Purkinje cells exhibited a modulation of simple spike discharges 180° out of phase to head velocity, the mean amplitude of modulation being 9.3% of the mean discharge rate. During HOKR, these cells also exhibited modulation by 13.8% in phase to creen velocity. No specific localization was found as to the relative intensities of these responses. It is estimated that an eye velocity component accounts for 18–20% and an eye position component for 5–14% of the responses of floccular H-zone Purkinje cells during HVOR and HOKR.