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1. The purpose of this study is 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 [15O]-H2O 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 (FEFs) and of the hand- and eye-movement-related regions of the supplementary motor area (SMA). 3. Friston's statistical parametric mapping (SPM) method was used to identify significant changes in rCBF associated with task performance. Because SPM does not take advantage of the anatomic 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 with 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 for identification of 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 FEFs, 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 ...

The ocular-following responses elicited by brief unexpected movements of the visual scene were studied in human subjects. Response latencies varied with the type of stimulus and decreased systematically with increasing stimulus speed but, unlike those of monkeys, were not solely determined by the temporal frequency generated by sine-wave stimuli. Minimum latencies (70-75 ms) were considerably shorter than those reported for other visually driven eye movements. The magnitude of the responses to sine-wave stimuli changed markedly with stimulus speed and only slightly with spatial frequency over the ranges used. When normalized with respect to spatial frequency, all responses shared the same dependence on temporal frequency (band-pass characteristics with a peak at 16 Hz), indicating that temporal frequency, rather than speed per se, was the limiting factor over the entire range examined. This suggests that the underlying motion detectors respond to the local changes in luminance associated with the motion of the scene. Movements of the scene in the immediate wake of a saccadic eye movement were on average twice as effective as movements 600 ms later: post-saccadic enhancement. Less enhancement was seen in the wake of saccade-like shifts of the scene, which themselves elicited weak ocular following, something not seen in the wake of real saccades. We suggest that there are central mechanisms that, on the one hand, prevent the ocular-following system from tracking the visual disturbances created by saccades but, on the other, promote tracking of any subsequent disturbance and thereby help to suppress post-saccadic drift. Partitioning the visual scene into central and peripheral regions revealed that motion in the periphery can exert a weak modulatory influence on ocularfollowing responses resulting from motion at the center. We suggest that this may help the moving observer to stabilize his/her eyes on nearby stationary objects.

We studied pursuit eye movements in seven normal human subjects with the scleral search-coil technique. The initial eye movements in response to unpredictable changes in target motion were analyzed to determine the effect of target velocity and position on the latency and acceleration of the response. By restricting our analysis to the presaccadic portion of the response we were able to eliminate any saccadic interactions, and the randomized stimulus presentation minimized anticipatory responses. This approach has allowed us to characterize a part of the smooth-pursuit system that is dependent primarily on retinal image properties. The latency of the smooth-pursuit response was very consistent, with a mean of 100 +/- 5 ms to targets moving 5 degrees/s or faster. The responses were the same whether the velocity step was presented when the target was initially stationary or after tracking was established. The latency did increase for lower velocity targets; this increase was well described by a latency model requiring a minimum target movement of 0.028 degrees, in addition to a fixed processing time of 98 ms. The presaccadic accelerations were fairly low, and increased with target velocity until an acceleration of about 50 degrees/s2 was reached for target velocities of 10 degrees/s. Higher velocities produced only a slight increase in eye acceleration. When the target motion was adjusted so that the retinal image slip occurred at increasing distances from the fovea, the accelerations declined until no presaccadic response was measurable when the image slip started 15 degrees from the fovea. The smooth-pursuit response to a step of target position was a brief acceleration; this response occurred even when an oppositely directed velocity stimulus was present. The latency of the pursuit response to such a step was also approximately 100 ms. This result seems consistent with the idea that sensory pathways act as a low-pass spatiotemporal filter of the retinal input, effectively converting position steps into briefly moving stimuli. There was a large asymmetry in the responses to position steps: the accelerations were much greater when the position step of the target was away from the direction of tracking, compared with steps in the direction of tracking. The asymmetry may be due to the addition of a fixed slowing of the eyes whenever the target image disappears from the foveal region. When saccades were delayed by step-ramp stimuli, eye accelerations increased markedly approximately 200 ms after stimulus onset.(ABSTRACT TRUNCATED AT 400 WORDS)