Effects of optokinetic velocity and medial vestibulo-cerebellum lesions on vestibulo-ocular reflex direction adaptation in the cat.

Adaptive horizontal vestibulo-ocular reflex eye movements in response to vertical (pitch) rotations were produced by exposing three cats to synchronized horizontal optokinetic and vertical vestibular oscillations at 0.25 Hz. The effects of optokinetic stimulus velocity (6-80 degrees/s peak) and nodulo-uvular cerebellum lesions were studied. All optokinetic velocities elicited vestibulo-ocular reflex direction adaptation. though 6 degrees/s stimuli were somewhat less effective. Restricted aspirations of cerebellar vermis lobules IX and X in two cats resulted in reduced but still clearly evident adaptation.