Behavior of floccular Purkinje cells correlated with adaptation of vestibulo-ocular reflex in pigmented rabbits.

The responsiveness of floccular Purkinje cells to head oscillations was examined in alert pigmented rabbits subjected to adaptation of horizontal vestibulo-ocular reflex (HVOR) under three different combinations of turntable and screen oscillations. Purkinje cells involved in the HVOR control (H-zone cells) were identified by local stimulation effects that induced horizontal eye movements. In control states, simple spike discharges of H-zone cells were modulated predominantly out of phase with the velocity of sinusoidal turntable oscillation (0.1Hz, 5 degrees peak-to-peak). A sustained 180 degrees outphase combination (5 degrees turntable and 5 degrees screen oscillation) was found to increase the average HVOR gain by 0.16, at which point the majority of H-zone cells increased the outphase simple spike modulation. A sustained inphase combination (5 degrees turntable and 5 degrees screen oscillation) decreased the average HVOR gain by 0.09, with the majority of H-zone cells decreasing the outphase simple spike modulation or becoming converted to the inphase modulation. With a vision-reversal combination (5 degrees turntable and 10 degrees screen oscillation), there was no change in the gain of the HVOR, but a moderate advancement in the phase. In this case, H-zone cells showed no appreciable changes in their simple spike modulation. Complex spike discharges of all H-zone cells tested were modulated in response to optokinetic stimuli involved in the combinations of turntable and screen oscillations. These results support the hypothesis that H-zone cells adaptively control HVOR dynamic characteristics through modification of mossy fiber responsiveness to head oscillation under influences of retinal error signals conveyed by climbing fiber afferents.