Discharge of pursuit neurons in the caudal part of the frontal eye fields during cross-axis vestibular-pursuit training in monkeys.

Previous studies in monkeys have shown that pursuit training during orthogonal whole body rotation results in task-dependent, predictive pursuit eye movements. We examined whether pursuit neurons in the frontal eye fields (FEF) are involved in predictive pursuit induced by vestibular-pursuit training. Two monkeys were rotated horizontally at 20 degrees/s for 0.5 s either rightward or leftward with random inter-trial intervals. This chair motion trajectory was synchronized with orthogonal target motion at 20 degrees/s for 0.5 s either upward or downward. Monkeys were rewarded for pursuing the target. Vertical pursuit eye velocities and discharge of 23 vertical pursuit neurons to vertical target motion were compared before training and during the last 5 min of the 25-45 min training. The latencies of discharge modulation of 61% of the neurons (14/23) shortened after vestibular-pursuit training in association with a shortening of pursuit latency. However, their discharge modulation occurred after 100 ms following the onset of pursuit eye velocity. Only four neurons (4/23 = 17%) discharged before the eye movement onset. A significant change was not observed in eye velocity and FEF pursuit neuron discharge during pursuit alone after training without vestibular stimulation. Vestibular stimulation alone without a target after training induced no clear response. These results suggest that the adaptive change in response to pursuit prediction was induced by vestibular inputs in the presence of target pursuit. FEF pursuit neurons are unlikely to be involved in the initial stage of generating predictive eye movements. We suggest that they may participate in the maintenance of predictive pursuit.