The effect of ablation of frontal eye-fields and superior colliculi on visual stability and movement discrimination in rhesus monkeys.

The neurological basis of the maintenance of a stable visual scene by means of a corollary discharge mechanism was investigated. Monkeys were trained to detect and respond to sudden rapid movement of a small spot of light in an otherwise totally dark environment. There was no evidence that after removal of the frontal eye-fields, superior colliculi, or caudal superior temporal sulcus the animals confused real movement of the target with retinal image movement caused by changing the position of head and eyes.

Brain damage and global stereopsis.

When a single object lies in front of or beyond the plane of fixation its retinal image lies on disparate positions in the two eyes. This 'local' retinal disparity is an excellent cue to depth, and retinal disparties of a few seconds of arc are detectable by people and monkeys. However, most visual scenes produce a complex array of contours in each eye and we can detect the disparity in the arrays despite the ambiguous nature of the disparities, i.

The projection of the temporal retina in rats, studied by retrograde transport of horseradish peroxidase.

Horseradish peroxidase (HRP) was injected unilaterally into the lateral geniculate nucleus or tectum, or both, in 26 hooded rats in order to mark the exact extent of the retina from which uncrossed optic axons arise. This region occupied about a quarter of the retina, in the temporal periphery, following thalamic injections, but a much smaller region following tectal injections. By comparing the proportions of HRP positive neurones in nasal and temporal retinae of both eyes it was shown that: (1) within the region supplying uncrossed axons the majority of the ganglion cells nevertheless project contralaterally, (2) a large proportion of the ganglion cells from the temporal crescent project bilaterally, which does not occur from the remainder of the retina, (3) ganglion cells of all sizes contribute to both ipsilateral and contralateral projections.

The retinal origin of uncrossed optic nerve fibres in rats and their role in visual discrimination.

An attempt was made to sever the optic chiasma in the mid-sagittal plane in 12 rats. This was successful in 8 animals. Provided there was no additional substantial damage to the uncrossed optic fibres the rats were able to relearn an intensity discrimination and to learn or relearn an orientation discrimination, although optokinetic following was abolished.

Changes in the retino-fugal pathways following cortical and tectal lesions in neonatal and adult rats.

Several months after unilateral removal of the striate cortex or superior colliculus, or both, in infant and adult rats the retinal projections were studied autoradiographically. The retinal projection areas in adult-operated animals were not different from those of unoperated controls, but aberrant pathways were found in the infant group. Following removal of striate cortex there was a small aberrant pathway to the lateral posterior nucleus of the thalamus (LP) and possibly to the pretectum.

The effects of unilateral cortical and tectal lesions on retinal ganglion cells in rats.

The ganglion cell layer of the retina was examined for retrograde transneuronal degeneration after removing the striate cortex unilaterally in infant or adult rats. No significant degeneration occurred, even after a survival time of 15 months, and the rat is therefore unlike other mammals in which the phenomenon has been studied. A possible explanation that most optic axons bifurcate in rats and that the tectal branch can sustain the ganglion cell after the branch to the dorsal lateral geniculate nucleus has degenerated following removal of striate cortex was ruled out by the demonstration that combined unilateral removal of striate cortex and superior colliculus in adults was similarly ineffective.

[The ipsilateral optic tracts in the rat. - II) Their role in visual discrimination].

Rats with compete section of the optic chiasma were able to relearn an intensity discrimination and to learn or relearn an orientation discrimination. The results unequivocally demonstrate that the uncrossed optic fibres can mediate two kinds of visual discrimination.

[The ipsilateral optic tracts in the rat. - I) Area of retinal origin].

An attempt was made to sever the optic chiasma in the mid-sagittal plane in 12 rats. This was successful in 8 animals. The area of retina giving rise to the uncrossed fibres was determined from the position of undegenerated retinal ganglion cells in each eye following section of the chiasma.

Effects of subcortical lesions on visual intensity discriminations in rats.

The role of several subcortical structures in visual intensity discrimination was examined by comparing the effects of localized lesions on a variety of intensity discriminations. In Experiment 1 light avoidance was unimpaired after lesions of the ventral lateral geniculate nucleus (LGNv), nucleus lateralis posterior (TLP), nucleus posterior of Gurdijian (NPG), dorsal pretectum (PTd), and ventral pretectum (PTv). The LGNv, TLP, NPG and PTv, but not the PTd, groups were impaired on a simultaneous black versus white (BW) discrimination in Experiment 2.

The role of the ventral lateral geniculate nucleus and posterior thalamus in intensity discrimination in rats.

The role of several subcortical structures in intensity discrimination was studies by examining the effects of localized lesions on intensity and orientation discrimination. In experiment 1 rats with lesions confined to the ventral lateral geniculate nucleus (LGNv) or posterior thalamus were specifically impaired on postoperative acquisition of the intensity discrimination compared with sham operated controls or rats with destruction of the superior colliculi. The lesions had no effect on the orientation discrimination unless the primary visual pathways were also damaged.