CORTICAL CONTROL OF VESTIBULAR-GUIDED SACCADES IN MAN

Memory-guided saccades, made to a remembered location to which gaze was directed before a passive body rotation (i.e. with a vestibular input), were electro-oculographically recorded in 24 patients with various cortical lesions and in 18 control subjects. Anticipation and latency, direction errors and accuracy of the first saccade, stability of eye position in darkness and final eye position were quantified. Patients were divined into small groups, each with lesions affecting one of the following cortical areas: left or right frontal eye field (FEF), left or right prefrontal cortex (al-ea 46 of Brodmann) (PFC), left supplementary eye field (SEF), left or right posterior parietal cortex (PPC) and right parieto-temporal cortex (PTC). There were some abnormalities in the results of the right FEF group, concerning anticipation, direction en ors and latency of the first saccade, but no abnormality in the accuracy of the first saccade or of the final eye position. Results in the left FEF group were normal. Accuracy of the first saccade was impaired in the SEF group, bilaterally Final eye position was also inaccurate in the SEF group. In both PFC groups, significant and, in general, bilateral abnormalities existed for all tested parameters. Accuracy of the first saccade was impaired in the PTC group, leftwards. In contrast, the results in both PPC groups were not significantly different from those of control subjects. Our results suggest that (i) the PFC is involved in the memorization of saccade goals probably encoded in spatiotopic coordinates, (ii) the SEF: but not the FEF is involved in the control of accuracy of these vestibular-derived goal-directed saccades, (iii) the PTC (i.e. the vestibular cortex), but not the PPC, is involved in the control of such saccades. Therefore, a cortical network different from that involved in the control of memory-guided saccades made to visual targets, with only the PFC in common, could control vestibular-derived goal-directed saccades.