Abstract
For pursuit of small objects moving slowly and smoothly in space close to the observer, two independent eye movement systems are used: frontal smooth pursuit and vergence-tracking. Signals for both systems must be synthesized for pursuit of a target moving in three dimensions. Recent studies in our laboratory have demonstrated that among the cerebral cortical pursuit areas, three dimensional (3D) pursuit signals are generated primarily in the frontal eye fields (e.g. Akao et al. 2005). To drive ocular motoneurons, 3D pursuit signals must be sorted into signals for each eye movement system and finally into oculomotor signals. Studies in our laboratory indicate that such conversion was not detected in the cerebeller floccular region (Tsubuku et al. Soc Neurosci Abstr 2004). The cerebellar dorsal vermis is well known as another pathway for frontal pursuit. To examine whether vergence signals are present in this area, we examined simple-spike discharge of vermal pursuit Purkinje (P-) cells in 2 monkeys. Of a total of 64 P-cells that were examined during both frontal pursuit and vergence-tracking, 50% discharged for both, 37.5% only for vergence-tracking, and 12.5% only for frontal pursuit. These results indicate that about 90% of vermal pursuit P-cells discharged for vergence-tracking and that half of them still had 3D pursuit signals. Majority (71%) of these P-cells discharged before onset of vergence eye movements with the typical lead time of 50 ms, suggesting their involvement in the initiation of vergence eye movements. [J Physiol Sci. 2006;56 Suppl:S93]
