Role of cerebellar dorsal vermis in generation of pursuit eye movements in three dimensional space

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Frontal-eyed primates use both smooth-pursuit in fronto-parallel planes and pursuit-in-depth to track objects moving slowly in three-dimensional (3D) space. 3D-pursuit signals are represented in frontal eye fields (FEF). Previous studies have shown that the cerebellar dorsal vermis is involved in smooth-pursuit and the control of rotational vestibulo-ocular reflex (VOR). To understand how it is involved in processing of 3D-pursuit signals and translational VOR, we performed two series of studies in monkeys. In the first year, we characterized pursuit signals. In 40% of vermal pursuit P-cells, 3D-pursuit signals were observed. However, the majority of vermal pursuit P-cells (60%) discharged either for vergence-pursuit or frontal-pursuit. Furthermore, the majority of vergence pursuit P-cells discharged for convergence and discharged before the onset of eye movements. Muscimol infusion into the dorsal vermis resulted in a reduction of peak convergent eye velocity and of initial convergent … More eye acceleration. These results suggest involvement of the dorsal vermis in decomposition of 3D-pursuit signals into frontal and depth components. In the second year, we tested discharge of vermal P-cells during right/left translation by passively moving the whole body while a target was presented at different viewing distances. The target was moved either with the whole body or stayed stationary in virtual space. Results were compared with those obtained in FEF pursuit neurons. The majority of vermal pursuit P-cells that were activated by right/left translation had horizontal preferred directions. In contrast, the majority of pursuit P-cells that had preferred directions in vertical directions or pursuit-in-depth rarely responded to right/left translation. During target stationary in space during translation, discharge modulation was correlated with resultant horizontal eye velocity. These results suggest that signals carried by FEF pursuit neurons during whole body translation are sent to the dorsal vermis for further processing of pursuit signals during translation. Less