Vergence eye movement signals in the cerebellar dorsal vermis.

We examined simple-spike activity of Purkinje cells (P-cells) that responded during a search task which required both vergence-and frontal-pursuit. Of a total of 100 responding P-cells, 16% discharged only for frontal-pursuit, 43% only for vergence-pursuit, and 41% for both. Thus, the majority of vermal pursuit P-cells modulated their activity during vergence-pursuit. These P-cells also discharged for vergence eye movements induced by step target-motion in-depth. The majority of vergence related P-cells carried convergence signals with both eye velocity and position sensitivities, and they discharged before the onset of convergence eye movements. Muscimol infusion into the sites where convergence P-cells were recorded resulted in a reduction of peak convergence eye velocity, of initial convergence eye acceleration, and of frontal-pursuit eye velocity. These results suggest specific involvement of the dorsal vermis in vergence eye movements.