STIMULATION-EVOKED SACCADES FROM THE DORSOMEDIAL FRONTAL-CORTEX OF THE RHESUS-MONKEY FOLLOWING LESIONS OF THE FRONTAL EYE FIELDS AND SUPERIOR COLLICULUS

This study examined whether signals for the generation of eye movement s from the dorsomedial frontal cortex (DMFC) reach brainstem oculomoto r centers either through the frontal eye fields (FEF) or through the s uperior colliculi (SC). The DMFC was stimulated when the monkeys studi ed were intact and after either one FEF or one SC was ablated. Followi ng lesions of either the FEF or SC, the topographic order of the DMFC was largely preserved. After either lesion, stimulation of anterior DM FC sites still evoked saccades that terminated in contralateral space, and stimulation of posterior DMFC sites still evoked saccades that te rminated in central space. The probability of evoking saccades decreas ed and the latency to evoke saccades increased as fixation neared the termination zone (a restricted region within craniotopic space) both b efore and after either lesion. Ablation of the SC. but not of the FEF, eliminated the saccadic inhibition to visual targets which resulted w hen the DMFC was stimulated in the intact animal. The findings suggest that additional channels besides those coursing through the FEF and S C are utilized by the DMFC to access the saccade generator in the brai nstem.