Neuronal events correlated with long-term adaptation of the horizontal vestibulo-ocular reflex in the primate flocculus.

The activity of flocculus Purkinje cells was examined in Japanese monkeys during sustained vestibular-visual stimulation which caused adaptation of the horizontal vestibulo-ocular reflex (H-VOR). In the floccular area related to the H-VOR by microstimulation. Purkinje cells consistently changed their simple spike responsiveness to head rotation in parallel with the adaptive H-VOR gain change. Similar changes occurred even after the H-VOR had been extinguished by lesioning of the vestibular nuclei. The complex spike discharge, on the other hand, modulated during vestibular-visual stimulation with a reciprocal pattern to the adaptive changes in the simple spike discharge. These results support the hypothesis that the flocculus adaptively modifies the H-VOR through their simple spike activity under the influence of visual climbing fiber signals.