THE EFFECTS OF COMBINED SUPERIOR TEMPORAL POLYSENSORY AREA AND FRONTAL EYE FIELD LESIONS ON EYE-MOVEMENTS IN THE MACAQUE MONKEY

We previously found [42] that lesions of the superior temporal polysen sory area (STP) cause temporary deficits in the production of eye move ments. In order to both define regions participating in the ensuing re covery and to further explore the cortical control of eye movements, w e examined the effects of addition of frontal eye field (FEF) lesions to STP lesions, on visual fixation, saccadic eye movements, and smooth pursuit eye movements. Three monkeys received bilateral STP lesions f ollowed by a FEF lesion and as a control, an additional monkey receive d a bilateral inferior temporal cortex (IT) lesion followed by a FEF l esion. All animals had a profound impairment in foveating the central fixation point. This impairment was completely eliminated by turning o n a dim light in the testing chamber. Large neglect-like impairments i n making saccades were only seen after combined STP and FEF lesions. I mpairments in making smooth pursuit eye movements after combined lesio ns of STP and FEF were larger than those seen after STP lesions but wi thin the range of deficits that have been reported after FEF lesions a lone. The impairment of visual fixation in darkness and the lack of im pairment under conditions of dim illumination appear to reflect a spec ific role for the FEF in spatial orientation in the absence of visual landmarks. The FEF also appears to play a more critical role than STP in smooth pursuit. By contrast, STP and the FEF appear to work coopera tively with respect to the production of saccades. We suggest that cor tical oculomotor control can flow either through the midbrain or throu gh the FEF and that the FEF pathway is specifically involved in tasks with a discontiguity between the stimuli and the behavioral response w hile the midbrain pathways are preferentially involved in more stimulu s-driven eye movements.