THE FUNCTION OF THE CEREBELLAR UVULA IN MONKEY DURING OPTOKINETIC ANDPURSUIT EYE-MOVEMENTS - SINGLE-UNIT RESPONSES AND LESION EFFECTS

The cerebellum is known to participate in visually guided eye movement s. The cerebellar uvula receives projections from pontine nuclei that have been implicated in visual motion processing and the generation of smooth pursuit. Single-unit and lesion studies were conducted to dete rmine how the uvula might further process these input signals. Purkinj e cells and input fibers were recorded during a variety of visual and oculomotor paradigms. Most Purkinje cells were modulated in either an excitatory or inhibitory fashion by prolonged, horizontal optokinetic drum rotation. A small proportion of cells responded during smooth tra cking of a small spot of light. As a paradox to the physiological data , lesions of the uvula produced a profound effect on smooth-pursuit ey e movements. Initial eye velocity for pursuit in the direction contrav ersive to the lesion site was increased substantially following lesion s in comparison with prelesion controls. The lesions also affected opt okinetic nystagmus in the direction contraversive to the lesion, but n ot as drastically as they did pursuit. Overall the results suggest tha t the uvula is not in the neuronal pathway that directly controls purs uit, but instead serves to adjust the gain of this system as a result of abnormal periods of motion of the visual world.