Saccades induced by stimulation of the frontal eye fields: interaction with voluntary and reflexive eye movements.

Saccadic eye movements were evoked in alert monkeys by electrical stimulation of the frontal eye fields (FEF). The interaction of FEF movements with voluntary saccades, pursuit, and vestibular nystagmus (VN) was examined. An FEF saccade in one direction could be evoked as little as 10 msec after the onset of a natural rapid movement (saccade, fast phase of VN) in the opposite direction. Thus, refractory periods between similar eye movements are directionally specific. The frequency of evoked FEF saccades following natural slow movements (pursuit, slow phase of VN) in either direction was reduced as though saccade thresholds were elevated. The FEF appears capable of modulating any ongoing eye movement.