CORTICAL CONTROL OF REFLEXIVE VISUALLY-GUIDED SACCADES

Abstract

Reflexive visually-guided saccade triggering may be facilitated or inhibited by the cerebral cortex. To study this control, saccades made towards suddenly appearing visual targets (saccade task) or away from them (antisaccade task) were recorded electro-oculographically in 45 patients with limited unilateral cerebral infarction. Lesions affected (1) the superior part of the angular gyrus (area 39 of Brodmann) in the posterior parietal cortex (PPC), (2) the dorsolateral prefrontal cortex (PFC) (area 46 of Brodmann), (3) the frontal eye field (FEF), or (4) the supplementary motor area (SMA). As these 4 types of lesions were located either in the right or the left cerebral hemisphere, patients were divided into 8 groups. Saccade latency, in the saccade task, and the percentage of errors (misdirected saccades made towards the visual target), in the antisaccade task, were compared in each group of patients with the values of 20 control subjects. In the saccade task, saccade latency was significantly increased bilaterally in the right PPC group. In the left PPC group, the increase in latency was less marked, and significant only for saccades made contralaterally to the lesion. In the different frontal groups, latency was unchanged or only slightly increased. These results confirm that the main area facilitating the triggering of reflexive visually-guided saccades is located in the PPC, in or near the superior part of the angular gyrus. The difference between right and left parietal lesions could be due to the predominance of the right hemisphere in the control of these saccades. In the antisaccade task, the percentage of errors was significantly increased bilaterally in both PFC groups compared with the control group and also to the FEF and SMA groups. These results suggest that the PFC is the main area in the cerebral hemisphere inhibiting reflexive visually-guided saccades.