Extrastriate cortical neurons correlated with ocular convergence in the cat

Effect of motion stimulation without changing binocular disparity on stereopsis in strabismus patients

PURPOSE

To evaluate the effect of motion stimulation without changing binocular disparity on stereopsis in strabismic patients.

METHODS

Static and moving stereopsis were measured in 120 normal children and 30 strabismic patients (9 esotropia, 14 exotropia, 7 intermittent exotropia). Using a portable game device (PSP; SONY, Japan), we created stereoscopic targets and produced stereopsis using a closed tube binocular viewing device. Stereoscopic disparity of targets was adjusted in 20 steps of 100 s each over a range from 2000 s to 100 s. In stereo testing using our apparatus, static test targets were used for static stereograms (SS), and test targets with clockwise planar rotation were used for moving stereograms (MS) without changing binocular disparity.

RESULTS

All normal children were able to perceive stereopsis with stereoscopic disparity from 2000 s to 100 s, and were interested in our apparatus, more than the Titmus stereo tests. All esotropic patients failed both SS and MS. In the exotropic patients (14 exotropia and 17 intermittent exotropia patients), 19 (90.4%) passed the MS, and 13 (61.9%) passed the SS.

CONCLUSION

The exotropic patient might be able to perceive the binocular stereopsis by moving stereogram that was created by adding clockwise planner rotation without changing the binocular disparity to the static stereopsis target.

Visual cortical contribution to open-loop and feed-back control of convergence eye movements in the cat

Open-loop and closed loop controls in convergence eye movement have been reported by human psycho-physical studies. To investigate the visual cortical involvement in open-loop convergence eye movement, we trained a cat to elicit anticipatory convergence (convergence eye movement before the onset of target movement) by using an approaching visual target with a preceding alarm signal. After 1-2 weeks of training, anticipatory convergence was observed in more than half of the trials in seven cats. The frequency of occurrence of anticipatory convergence was significantly decreased after electrocoagulation in the convergence-related region of the lateral suprasylvian (LS) area, an extrastriate visual cortex of the cat. On the other hand, the localized injection of Muscimol, a GABA-A agonist, reduced visually evoked convergence, but caused no significant effects to anticipatory convergence. These differential results suggest that the LS plays a role in both open-loop and feed-back control of convergence eye movement, and a GABA-A sensitive subregion is involved in the feed-back control of convergence eye movement.

Present concepts of oculomotor organization

This chapter gives an introduction to the oculomotor system, thus providing a framework for the subsequent chapters. This chapter describes the characteristics, and outlines the structures involved, of the five basic types of eye movements, for gaze holding ("neural integrator") and eye movements in three dimensions (Listing's law, pulleys).

Spatial disparity sensitivity in area PMLS of the Siamese cat

Previous studies of the visual system of Siamese cats have shown that binocular cells are scarce in areas 17, 18 and 19, yet significantly more abundant in suprasylvian areas such as the postero-medial lateral suprasylvian area (PMLS). The present study aims at evaluating the sensitivity to spatial disparity of PMLS binocular cells in paralyzed and anesthetized Siamese cats. Centrally located receptive fields were mapped, separated using prisms and then stimulated simultaneously using two luminous bars optimally adjusted to the size of the excitatory receptive fields. Delays were introduced in the arrival of the luminous bars in the receptive fields so as to create the desired spatial disparities. Results indicate that approximately a third of PMLS units are binocular and that these binocular cells can detect spatial disparity cues. Indeed, although the sample was relatively small, cells of the tuned excitatory (14/34), tuned inhibitory (2/34), near (6/34) and far (1/34) types were identified. The spatial selectivity, as measured by the width at half height of the tuning curves of the excitatory and inhibitory cells and the slopes of the near and far cells, was similar to that obtained in PMLS of normal cats but not as precise as that found for primary visual areas in these animals. This suggests that these cells might serve as a substrate for coarse stereopsis.

The properties of convergence eye movements evoked from the rostral and caudal lateral suprasylvian cortex in the cat

Convergence eye movements were evoked in the lateral suprasylvian cortex (LS cortex) in the cat. Three effective regions were found: the rostral and caudal parts of the postero-medial LS cortex (the PMLS) and the rostral part of the postero-lateral LS cortex (the PLLS). These three areas represent the central and paracentral visual fields in the published retinotopic map (Palmer et al., 1978). Convergence eye movements evoked from the caudal PMLS were divided into two groups based on their latencies; the short-latency components (SLC) and long-latency components (LLC). The SLC and the LLC had differences in their symmetry of right and left eye movements during vergence eye movement. The SLC had symmetric right and left eye components and the LLC had dominant contralateral eye components. In the rostral PMLS, latencies of evoked convergence eye movement were comparable to those of the caudal PMLS, but they did not divided into two groups. Convergence eye movements evoked from the PLLS had longer latencies than those from the PMLS and asymmetric right and left eye components. It is suggested that different subregions in the LS cortex contribute to the control of convergence eye movement, playing different roles.

Effects of localized lesions in the lateral suprasylvian cortex on convergence eye movement in cats

We evaluated the effects of electrolytic lesions in the extrastriate cortical area on the amplitudes and velocities of vergence eye movements in six alert cats that were trained to track a target moving in depth. Bilateral or unilateral lesions in the lateral suprasylvian (LS) cortex reduced the amplitudes and velocities of vergence eye movements, but the positive correlation between them was maintained. Furthermore, unilateral lesions changed the symmetry of eye movements. Movements of the left eye were decreased by lesions in the right LS cortex, resulting in asymmetric vergence eye movement with right eye predominance, and vice versa. These results support the hypothesis that the LS cortex plays an essential role in controlling vergence eye movement.

Human cortical areas activated in relation to vergence eye movements-a PET study

Human cortical areas activated in relation to vergence eye movements were determined using positron emission tomography. Binocular disparity-driven visual stimuli were presented using a head-mounted display. Eye movements were monitored continuously by an infrared limbus tracker. A combination of a bar and a cross was used as the target. In the vergence task, subjects were instructed to follow an approaching bar, while ignoring a stationary cross. Activation in relation to vergence eye movement was discriminated from activation in relation to motion vision by using the ignore-bar task as the control. In the ignore-bar task, subjects were instructed to fixate on a stationary cross, while ignoring an approaching bar. The fixation task was used as the basic control for both the vergence and the ignore-bar tasks. Areas of activation in relation to vergence eye movements were found in the bilateral temporooccipital junction, the left inferior parietal lobule, and the right fusiform gyrus by comparing regional cerebral flow between the vergence and ignore-bar tasks and by the conjunctive analyses of vergence-vs-ignore comparison with vergence-vs-fixation comparison.

Changes in oculomotor functions before and after loading of a 3-D visually-guided task by using a head-mounted display

Changes in visual and oculomotor functions were tested in eight young volunteer subjects after performing a 3-D visually-guided task for 25 min. The visual stimuli were given by using a head-mounted display. No significant change was detected in the AC/A ratio and the stereo acuity. Changes were found in refraction and ocular convergence. Slight but significant hyperopic changes were detected in refraction after the task. The mean amplitude of convergence eye movement elicited by test stimuli after the task was significantly changed in the pooled data. They were significantly reduced when the subjects were tested by the disparity step of 0.7 degrees, but significantly increased when tested by the step of 6 degrees. The mean amplitudes were not significantly changed after the task when the subjects were tested by the intermediate disparity steps of 1.5 and 3 degrees. In data obtained for each subject, the amplitude of ocular convergence evoked by test stimuli after the task was reduced significantly in most subjects. In the majority of subjects, however, the results were not consistently significant when they were tested by step stimuli with different disparities. In only a few subjects, the changes were consistently significant except when the largest disparity was tested. On the other hand, the mean peak velocities of ocular convergence after the task were not significantly changed in the pooled data. In individual subjects, the changes of velocities of ocular convergence evoked by test stimuli after the task were more variable: they increased in some subjects but decreased in other subjects. Consequently, in only one subject, both amplitudes and peak velocities of ocular convergence tested by the disparity steps of 0.7, 1.5 and 3 degrees were consistently reduced after the task. The changes in refraction or ocular convergence found in this study were relatively small, and were not in the pathological range. The significance of these data are discussed. The results of the present study provide the basis for the more detailed analyses of the human factor in the head-mounted display.

Roles of the lateral suprasylvian cortex in convergence eye movement in cats

Ocular convergence and lens accomodation were evoked by microstimulation in the lateral suprasylvian area (LS cortex) in the parieto-occipital cortex in the cat. Electrolytic lesions in LS cortex reduced the amplitude and velocity of ocular convergence. Neurons in LS cortex discharged in relation to ocular convergence and/or lens accommodation. These results support the hypothesis that the LS cortex plays an important role in controlling ocular convergence The LS cortex receives visual inputs from cortical visual areas 17, 18 and 19, and in addition from the superior colliculus through the LP nucleus of the thalamus. Electrophysiological recordings have revealed that these visual inputs, which include cues about 3-dimensional target motion, are integrated in the LS cortex. The integrated output from LS cortex may provide the brainstem motor centers with the neural signals that facilitate eye movements, especially when the target is moving at high speeds. Outputs from the LS cortex travel directly to brainstem structures including the superior colliculus and pretectum. Evidence from monkey suggests that information may also travel to the mesencephalic reticular formation, where neurons have been recorded that are related to ocular convergence, lens accomodation or both. Although comparable data is lacking in the cat, it is suggested that the efferent circuit from the LS cortex to the motor nuclei in the brainstem included both the superior colliculus and the mesencephalic reticular formation. It is also suggested that this pathway is rather short, given that the mean latency of the early component of evoked disjunctive eye movements was approximately 60 ms.