A Positron Emission Tomography Study of Voluntary Saccadic Eye Movements and Spatial Working Memory. Sweeney, J.A., M.A. Mintun, S. Kwee, M.B. Wiseman, D.L. Brown, D.R. Rosenberg, J.R. Carl. The Neurobehavioral Studies Program, Departments of Psychiatry, Neurology, Radiology and Ophthalmology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, 15213.
APStracts 2:0265N, 1995.
SUMMARY AND CONCLUSIONS
1. The purpose of this study was to define the cortical regions that subserve voluntary saccadic eye movements and spatial working memory in humans. 2. Regional cerebral blood flow (rCBF) during performance of oculomotor tasks was measured with [ 15 O]-H 2 O positron emission tomography (PET). Eleven well- trained, healthy young adults performed the following tasks: visual fixation, visually guided saccades, antisaccades (a task in which subjects made saccades away from rather than toward peripheral targets), and either an oculomotor delayed response (ODR -- a task requiring memory-guided saccades after a delay period) or a conditional antisaccade task (a task in which the color of the peripheral target determined whether a saccade toward or away from the target was required). An additional six subjects performed a sequential hand movement task to compare localization of hand-related motor cortex and the frontal eye fields (FEF), and of the hand and eye movement-related regions of the supplementary motor area (SMA). 3. Friston's Statistical Parametric Mapping (SPM) method (Friston et al. 1991) was used to identify significant changes in rCBF associated with task performance. Since SPM does not take advantage of the anatomical information available in Magnetic Resonance (MR) scans, each subject's PET scan was registered to that individual's MR scan, after which all PET and MR studies were transformed to conform to a standard reference MR image set. Subtraction images were visually inspected, while overlayed on the reference MR scan to which PET images had been aligned, in order to confirm anatomic localization of significant rCBF changes. 4. Compared to visual fixation, performing visually guided saccades led to a significant bilateral activation in FEF, cerebellum, striate cortex and posterior temporal cortex. Right posterior thalamus activation was also observed. 5. The visually guided saccade task served as the comparison task for the ODR, antisaccade and conditional antisaccade tasks in order to identify task-related changes in rCBF beyond those associated with saccade execution. Performance on the ODR task was associated with a bilateral increase of rCBF in FEF, SMA, dorsolateral prefrontal cortex (DLPFC), and posterior parietal cortex. The cortical regions of increased regional blood flow during the ODR task also showed increased rCBF during the antisaccade task; however, FEF and SMA activations were significant only in the right hemisphere. These findings closely parallel those of single cell recording studies with behaving monkeys in indicating that FEF, DLPFC, SMA and posterior parietal cortex perform computational activity for voluntary purposive saccades. 6. Comparison of PET scans obtained during performance of eye movement and hand movement tasks indicated that peak activations in FEF were located approximately 2 cm lateral and 1 cm anterior to those of hand-related motor cortex. The oculomotor area of SMA, the supplementary eye field (SEF), was located approximately 7-8 mm anterior and superior to the hand-related area of SMA. 7. During performance of antisaccade and ODR tasks, rCBF was significantly lower in ventromedial prefrontal cortex, along the rectus gyrus, and in ventral anterior cingulate cortex than during the visually guided saccade and fixation tasks. During the antisaccade task, the ventral region of lower rCBF involved medial structures including left ventral striatum and bilateral medial temporal-limbic cortex. During the ODR task, the ventral aspect of the region of lower rCBF extended laterally, rather than medially, to include the temporal poles. The lower blood flow observed in ventromedial prefrontal cortex (PFC) during both the antisaccade and ODR tasks, relative to the visually guided saccade and fixation tasks, suggests that modulation of output from ventromedial PFC to limbic cortex and the striatum may play a role in the voluntary control of saccadic eye movements, possibly in the suppression of responses that would interrupt ongoing purposive behavior. 8. During the ODR task, rCBF changes in DLPFC, FEF, SMA, posterior parietal cortex, ventral anterior cingulate and orbital frontal cortex were highly intercorrelated. A similar pattern of activation across cortical regions was observed during the antisaccade task, with the exception that activation in SMA was independent from rCBF changes observed in other cortical regions. These findings suggest that widely distributed cortico-cortical neural circuitry mediates the voluntary control of saccades in humans. 

Received 24 April 1995; accepted in final form 8 August 1995.
APS Manuscript Number J272-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 September 1995.