Effects of ablation of flocculus and paraflocculus of eye movements in primate

Abstract

Eye movements were recorded in 4 rhesus monkeys [M. mulatta] before and after bilateral ablations of the flocculi and portions of the paraflocculi (flocculectomy). Animals were trained to fixate and follow targets so that pursuit, saccades and vestibular and optokinetic nystagmus [OKN] could be quantitated. The flocculus and possibly paraflocculus apparently participate in the control of oculomotor reflexes that insure best visual acuity by preventing retinal slip. The flocculus serves both the specific needs of the fovea (pursuit, saccades and gaze holding) and the phylogenetically older requisite for stabilization of images on the retina during head rotation (VOR [vestibuloocular reflex] and OKN). The unpredictable effect of flocculectomy on VOR gain, postsaccadic drif and the waveforms of vertical nystagmus may reflect the basic regulatory role of the cerebellum so that inherent imperfections in oculomotor performance are exposed by removal of the flocculus.