Discharge of frontal eye field neurons during saccadic and following eye movements in unanesthetized monkeys.

The cortical mechanism of eye-movement control was investigated by recording single cell activity from the frontal eye field (FEF) in unanesthetized monkeys seated in a primate chair with head restrained. Two types of cells (I and II) were found. Type I neurons fired during voluntary saccades occurring in a given direction and during the fast phase of nystagmus. Cells of this type were silent during slow pursuit movement. Type II cells showed steady discharge when the eyes were oriented in a specific direction. These cells discharged also during smooth pursuit movements and the slow phase of nystagmus, provided that the eyes were moving across positions which would have been associated with neuronal activity had the eyes come to rest there. All of Type II and a few of Type I neurons were identified by antidromic response to stimulation of the cerebral peduncle. These results indicate that cortical neurons have patterns of discharge distinctly related either to saccadic or to pursuit movements, in line with the view that these two different types of eye movement are generated by distinct neuronal mechanisms.