Difference of flocculus and paraflocculus in the control of vestibulo-ocular and smooth pursuit eye movements in the primate.

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We examined the adaptability of macaque smooth pursuit eye movements and compared the responses of single unit activities of purkinje neurons during the adaptation of smooth pursuit between the cerebellar flocculus and its adjacent ventral paraflocculus. When the monkey pursued a target moving in 3^0step-l0^0/2rarnp mode, slow eye movement (4^0/s) first started lOOms after the onset of target movement, and later small saccade (2-3^0) occurred, which was followed by 8^0/s constant velocity smooth pursuit. Adaptive changes of the smooth pursuit velocity were seen when the target velocity was increased to 200/s or decreased to 5^0/s immediately after the onset of saccade for brief period(100-200ms). Moreover, the amplitude of saccade was modified and the latency for the saccade increased. The flocculus purkinje neurons exhibited modest responses during the eye movements to step-ramp target movements, but the ventral parafloccuhis purkinje neurons exhibited rather strong responses to the pursuit eye movements to step-ramp target movements. Neuronal changes correlated with the adaptation of the smooth pursuit was recognized in most (8 of 14 examined neurons) of ventral paraflocculus purkinje neurons, while the none of the flocculus purkinje neurons examined (12 neurons) showed responses correlated with adaptation of smooth pursuit. These results strongly suggest that the flocculus and ventral paraflocculus mediate different role in the control of smooth pursuit.