No-go neurons in the cerebellar oculomotor vermis and caudal fastigial nuclei: planning tracking eye movements
Anatomical locations of the Purkinje cells (P cells), showing modulations in activity during either saccadic or smooth-pursuit eye movements, during primate chair rotation, or in response to optokinetic stimulation, were studied in the posterior vermes of monkeys trained to move their eyes with a visual target. The majority (68.3%) of the responsive P cells were saccade-related units. They were located exclusively in vermal lobules VIc and VII: the oculomotor vermis. Most P cells sensitive to chair rotation were located in vermal lobules VIa,b and VIII (91.2%), designated as the paraoculomotor vermis. The P cells which modulated activity during smooth-pursuit eye movements, associated with eye position, or during optokinetic stimulation were found in both the oculomotor and paraoculomotor vermis. There were 25 P cells which modulated their activity during smooth pursuit in the oculomotor vermis. Among them, only three responded also to optokinetic stimulation but none was sensitive to chair-rotation stimulation. These findings suggest that the control of saccadic eye movements is the primary function of the oculomotor vermis.