JOURNALOFNEUROPHYSIOLOGY Vol. 58, No. 4, October 1987. Printed in U.S.A. Effects of Occipital Lobectomy Upon Eye Movements in Primate DAVID S. ZEE, RONALD J. TUSA, SUSAN J. HERDMAN, PHYLLIS H. BUTLER, AND GijNDEZ GUCER Departments ofNeurology, Ophthalmology, Neuroscience, and Neurosurgery, Johns Hopkins University SchoolofMedicine, 21205; and Department ofPhysical Therapy, University ofMaryland Schoolof Medicine, Baltimore, Maryland 21201 SUMMARY AND CONCLUSIONS 1. Eye movements were recorded before and after bilateral occipital lobectomy in six rhesus monkeys trained to fixate and to fol- low small targets. Striate cortex was com- pletely removed in two animals; small is- lands remained in the others. In all animals portions of extrastriate cortex were also re- moved but the medial superior temporal area in the superior temporal sulcus was largely spared. Optokinetic nystagmus (OKN) was markedly altered but not abol- ished in all animals. The immediate pursuit component of OKN was eliminated leading to a poor response to stimuli comprised of high frequencies. The velocity-storage com- ponent of OKN was present, but the maxi- mum value of OKN that could be achieved was decreased to 6 and 16”/s in the two most severely affected animals (preop, 65- 116O/s). The residual OKN was similar to that of afo- veate animals with a diminished response to high velocities of retinal-image motion and a temporal to nasal predominance during monocular viewing. 2. In the initial postoperative period all animals appeared completely blind. Within l-6 mo, however, they regained an ability to make visually guided saccades to, and smooth pursuit of, small targets. Saccades were nearly as accurate aspreoperatively, but saccade amplitudes were more variable and saccade latencies increased. In the two ani- mals with a complete removal of striate cor- tex, gains (eye velocity/target velocity) of smooth pursuit during sinusoidal tracking (6O”/s, 0.5 Hz) were 0.9 and 0.95. During tracking of step-ramp (Rashbass) stimuli with 6O”/s ramps, the average acceleration of the eyes during the first 120 ms of smooth pursuit was 189-278’ l s-’ l s-l (preop range, 154-4 18O l s-’ l ss’). In other respects, though, smooth pursuit was not normal. La- tencies were increased two- to threefold, and tracking was more variable. 3. Paradoxically, as visually guided sac- cadesand pursuit recovered, some other ocu- lar motor functions deteriorated. Spontane- ous and gaze-evoked nystagmus developed 3-6 mo after occipital lobectomy; the time constant of the neural eye-position integrator dropped to values as low as 2.6-4.8 s. The maximum slow-phase velocity of OKN also decreased. 4. The findings immediately after occipi- tal lobectomy indicate that in normal pri- mates occipital cortex is necessary for vi- sually guided saccades and smooth pursuit as well as for the immediate component of OKN. Occipital cortex also makes the pre- dominant contribution toward the gen- eration of the velocity-storage component of OKN. 5. The long-term changes after occipital lobectomy indicate that monkeys can learn to use extrastriate pathways to generate more volitional types of visual-ocular motor be- havior such as saccades and smooth pursuit. On the other hand, some of the more reflex- ive mechanisms that stabilize images on the retina eventually deteriorate, presumably from a chronic loss of visual feedback. 0022-3077/87 $1 SO Copyright 0 1987 The American Physiological Society 883 wnloaded from www.physiology.org/journal/jn by ${individualUser.givenNames} ${individualUser.surname} (132.174.254.155) on December 1, 2 Copyright © 1987 the American Physiological Society. All rights reserved.