Journal of Neuroscience, Vol 7, 3040-3058, Copyright © 1987 by Society for Neuroscience
The role of striate cortex in the guidance of eye movements in the monkey
MA Segraves, ME Goldberg, SY Deng, CJ Bruce, LG Ungerleider and M Mishkin
Laboratory of Sensorimotor Research, National Eye Institute, Bethesda, Maryland 20892.
We studied the effect of unilateral striate cortical ablations on smooth
pursuit and saccadic eye movements in the monkey. The monkeys made quite
accurate saccades to stationary stimuli in the field contralateral to the
lesion, and they readily pursued foveal targets moving in all directions.
However, when visual stimuli were stepped into the field contralateral to
the lesion and then began to move, thus insuring that the moving stimulus
was confined to the impaired visual hemifield, several oculomotor
abnormalities emerged. Saccades to moving stimuli presented in the impaired
field consistently undershot targets that moved away from the central
fixation point after the step, and overshot targets that moved back towards
the central fixation point. There was little or no smooth pursuit eye
velocity generated in any direction to moving stimuli in the impaired
field, and the monkeys could not generate smooth pursuit to stimuli
maintained a few degrees from the fovea in the impaired field, although
they were able to pursue such stimuli held in the normal field. Ablation of
striate cortex also affected the latencies of saccades. When step-ramp
stimuli were presented in the normal field, the monkeys delayed the
initiation of saccades to targets moving towards the central fixation
point, and hastened the initiation of saccades to targets moving away from
the central fixation point. By contrast, changes in the direction of target
movement did not affect the latencies of saccades into the impaired field.
The deficits seemed permanent, lasting as long as the monkeys were
tested--over 2 years in one case--but they were not total. Each monkey
could use stimuli moving into the affected field to develop some eye
velocity, although this residual ability had a much longer latency and
lower gain than that provided by the intact visual system. These results
show that striate cortex is intimately involved in the estimation of
stimulus velocity critical to the genesis of smooth pursuit and saccadic
eye movements.
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