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PubMed1998

Bilaterally projecting neurons in the two visual pathways of chicks.

By means of a double-labeling technique, we have investigated the organization of the bilateral thalamo-Wulst and tecto-rotundal projections in 2-day old chicks. After injecting fluorogold (FG) into one side of the visual Wulst and rhodamine B isothiocyanate (RITC) into the other side of the visual Wulst, the labeled neurons in the nucleus geniculatus lateralis pars dorsalis (GLd) were examined. Although the distribution areas of ipsilaterally and contralaterally labeled neurons overlap partly, very few double-labeled neurons were found (only 0.01% double-labeled neurons). This suggests that the ipsilateral and contralateral projections to the Wulst come from different neuronal populations of the thalamus. The FG and RITC were also injected into the rotundal nuclei (Rt) on each side of the thalamus and the labeled neurons in the optic tectum (TeO) were examined. In the TeO, the distribution areas of the neurons labeled ipsilaterally and contralaterally to Rt overlap completely and we found that up to 45% of the tectal cells were double-labeled by both FG and RITC. Therefore, many tectal neurons have axon collaterals so that they project to the Rt on both sides of the thalamus and must send information simultaneously to both sides of the brain. The differences in the structural organization of the two visual pathways are discussed with reference to the transmission of information to higher centers on both sides of the brain.

Animals↗
PubMed1994

Abnormal connectivity of the visual pathways in human albinos demonstrated by susceptibility-sensitized MRI.

We studied activation of the human visual cortex (VC) using susceptibility-sensitized MRI at 1.5 Tesla. Three albinos and six healthy controls underwent a series of monocular and binocular photic flash stimulation. Monocular stimulation in albinos caused predominant contralateral activation with a small, well-delineated area in the anterior part of the VC in the ipsilateral hemisphere. This finding was consistent with a chiasmal crossing anomaly in albinism. All controls had symmetric patterns of activation during monocular stimulation. Functional MRI represents a promising method for evaluation of the visual pathways in humans.

Adolescent↗
PubMed1982

Surgical and intensification procedures for defining visual pathways with cobaltous-lysine.

The introduction of heavy metals directly into living neuronal tissue has received little attention as a method for defining connections in the vertebrate nervous system. Procedures are described for the use of cobaltous-lysine to trace visual pathways with light microscopy. The success of the technique depends on a number of variables including: the method by which the tracer is applied, the survival period, and the method of intensification. Best results were obtained by soaking the optic nerve of living animals in the filling solution for 24 hr and by using a modification of the Timm's silver sulfide intensification procedure. Several factors that lead to poor results are discussed. Cobaltous-lysine is capable of both anterograde and retrograde labeling and can fill very sparse projections. Furthermore, the success of the fill can, at times, be evaluated prior to histology.

Animals↗
PubMed1978

Delayed visual evoked potentials with bilateral disease of the posterior visual pathway.

A man of 51 years presented with sudden onset of a confusional state and marked visual deterioration. The computerised transaxial tomogram showed a mass in the corpus callosum which had spread to involve both cerebral hemispheres. The visual evoked potential to pattern stimulus was delayed by about 20 ms. Necropsy confirmed the presence of an astrocytoma of the corpus callosum involving the optic radiation and occipital cortex on both sides. The anterior visual pathway was normal.

Astrocytoma↗
PubMed1983

Rapid decompression of anterior intracranial visual pathways with bromocriptine.

Bromocriptine mesylate (2-bromo-alpha-ergocryptine) has proved to be useful in reducing the size of prolactin-secreting pituitary adenomas, but little evidence has accumulated about its effectiveness within the first two weeks of therapy. The patient described herein showed a rapid reduction in the size of the suprasellar extension of a prolactinoma and a dramatic improvement of the primary visual field abnormalities within two weeks of starting bromocriptine therapy. This experience exemplifies the potential use of the drug in acutely decompressing the anterior intracranial visual pathways.

Adenoma↗
PubMed1992

Separate visual pathways for perception and action.

Accumulating neuropsychological, electrophysiological and behavioural evidence suggests that the neural substrates of visual perception may be quite distinct from those underlying the visual control of actions. In other words, the set of object descriptions that permit identification and recognition may be computed independently of the set of descriptions that allow an observer to shape the hand appropriately to pick up an object. We propose that the ventral stream of projections from the striate cortex to the inferotemporal cortex plays the major role in the perceptual identification of objects, while the dorsal stream projecting from the striate cortex to the posterior parietal region mediates the required sensorimotor transformations for visually guided actions directed at such objects.

Animals↗
PubMed1976

Organization of the tectofugal visual pathway in the pigeon: a retrograde transport study.

In birds, superficial laminae of the optic tectum receive a massive retinal input; the tectum in turn projects upon the nucleus rotundus thalami, which then sends its efferents to the ectostriatal core of the telencephalon. To examine the detailed organization of this principal ascending visual pathway, small injections of the marker horseradish peroxidase (HRP) were placed in various sites throughout the ectostriatum (E) or nucleus rotundus (Rt) in pigeons. Analysis of the resulting patterns of retrograde labeling indicates the tectofugal pathway to be comprised of at least five different channels. Cells which lie at various depths in the stratum griseum centrale (SGC) of the tectum project upon distinct subdivisions of nucleus rotundus. Anterior portions of Rt receive input from superficial-most cells in the SGC, while medial and more caudal portions of Rt are projected upon by deeper SGC neurons. A ventral subdivision of Rt was found to receive its primary input from two pretectal nuclei. Additional inputs to all portions of Rt arise from nucleus reticularis superior thalami. The various subdivisions of rotundus in turn project upon distinct portions of the ectostriatum. Thus, the segregation between the different input classes into Rt is largely retained at the telencephalic level. In contrast, the nucleus triangularis, a dorso-medial extension of Rt which receives its input from the deepest of all SGC neurons, sends its efferents to all parts of the ectostriatum.

Animals↗
PubMed1987

The scale of the visual pathways of mouse and rat.

Photoreceptors and neurons at various levels to cortex have been counted in mouse and rat. The ratios of neuron numbers (rat/mouse) are similar to the ratio of retinal areas or the squared ratio of eye sizes; so to a first approximation the two species have linearly scaled eyes, equal photoreceptor spacings (in micron), and visual pathways scaled numerically by the number of photoreceptors. With supplementary data from the literature, some of the functional implications of the design can be evaluated level by level. Overall, there is structural and computational economy, or even parsimony.

Animals↗
PubMed1986

Involvement of posterior visual pathways by optic nerve gliomas.

We describe the computed tomographic (CT) findings in seven children with optic nerve gliomas extending posterior to the chiasm. These tumors spread along the optic tracts and in five of seven cases, involved the lateral geniculate bodies and adjacent optic radiations. The propensity for these tumors to extend along both the anterior and posterior visual pathways aids in their diagnosis. An MR scan was obtained in one patient and identified an unexpected site of tumor extension as well as the mass seen by CT.

Child↗
PubMed1996

Discrimination performance and resolution capacity of uncrossed visual pathways in one-eyed albino rats.

Our recent study has demonstrated that adult rats with one eye removed at birth (OEB) relearn a discrimination between alternating black and white stripes, 30 mm wide each, oriented horizontally and vertically faster than control rats monocularly enucleated in adulthood (OET), when relearning is carried out after lesions of the visual cortex and transections of the optic tract contralateral to the remaining eye. Yet, we could not obtain the corresponding results in the acquisition of the discrimination following the same surgical treatments: OEBs did master the discrimination, whereas OETs did not. We hypothesized that a large discrepancy in OETs' performance between the acquisition and relearning occurred because the stripes were close to the limit of the resolution capacity of the uncrossed visual pathways (UXVPs), and hence that a better performance of OEBs was to indicate an increase in the resolution capacity, which resulted from reorganization of the UXVPs brought about by monocular enucleation at birth. To test the hypothesis we tried to approximate the limit of the resolution capacity of the UXVPs in OEBs and OETs using seven different sized test stripes ranging from 20 to 5 mm in width after both OEBs and OETs had relearned the discrimination of the 30 mm training stripes following the same surgical treatments mentioned above. It was found that the median width of the smallest stripes for OETs to discriminate was 10 mm, and that of OEBs 7.5 mm. Although OETs could not discriminate the smallest stripes which OEBs could, they were able to discriminate stripes one third smaller than those hypothesized. Based on these findings the possibility was discussed that the acquisition as well as the relearning of the discrimination of the 30 mm stripes mediated by the UXVPs in OEBs and OETs might not be influenced by the resolution capacity, but mostly, if not entirely, by the size of the visual field.

Animals↗
PubMed1982

The hemispheric dominance of cortical cells in the absence of direct visual pathways.

Unit recording was carried out in the visual cortex of split chiasm and optic tract-sectioned adult cats. From the proportions of the visually responsive and unresponsive cells found in each hemisphere of the operated cats it was concluded that the indirect pathway via the corpus callosum becomes visually inactive under these conditions. However, the direct geniculocortical pathway remains visually active. Thus, it was assumed that unilateral or bilateral elimination of the decussating pathway has a crucial effect on the amount of interhemispheric callosal transfer of basic visual functions.

Animals↗
PubMed1991

High-pass resolution perimetry and age-related loss of visual pathway neurons.

The normal, age-related decline of results of high-pass resolution perimetry (HRP) predicts a loss of approximately 9,000 retino-cortical neural channels per year of age, or about 1 channel each hour. Previously published counts of numbers of neurons in the optic nerve indicate a loss of approximately 5,000 neurons per year. The HRP results can be accounted for by postulating that neurons are lost at the same rate also in the geniculo-striate visual pathway.

Adolescent↗
PubMed1989

Two distinct visual pathways through the superficial pretectum in a percomorph teleost.

The connections of the superficial pretectum and of nucleus isthmi were examined in a percomorph teleost, Lepomis cyanellus. Horseradish peroxidase was injected either with a pin into the parvicellular nucleus of the superficial pretectum or pressure injected into nucleus isthmi; the isthmal injections retrogradely labelled the neurons of the magnocellular nucleus of the superficial pretectum. Two main visual pathways can be recognized: The first projects from the retina to the parvicellular nucleus, and then to the intermediate nucleus of the superficial pretectum, the inferior raphe nucleus, and the trochlear nucleus. The second projects from the retina via the optic tectum to the magnocellular nucleus of the superficial pretectum, and from there to nucleus isthmi and the lateral thalamic nucleus; nucleus isthmi and the lateral thalamic nucleus project back to the optic tectum, and nucleus isthmi also projects back to the magnocellular nucleus. The two pathways are interconnected to some extent because both nucleus isthmi and the optic tectum project to the parvicellular nucleus; nevertheless, we suggest that they may be functionally and evolutionarily distinct. Compared to percomorphs, the first pathway appears reduced in cyprinid teleosts such as goldfish. Furthermore, the magnocellular nucleus of the second pathway is completely different in cyprinids, both in cellular architecture and in efferent connections. A phylogenetic analysis suggests that cyprinid ancestors went through a period of reduced vision and that the magnocellular nucleus of the superficial pretectum in modern cyprinids has been either extensively modified from the primitive condition or lost entirely and replaced by a superficially similar structure.

Animals↗
PubMed1995

[Binocular photometer for measuring light perception in diseases of the visual pathway].

In patients with a reduction in visual function because of optic nerve neuritis, light sensitivity is tested to detect differences between the right and left eye in combination with the swinging flashlight test and visual evoked potential (VEP). A binocular Zeiss microscope was modified to use integrated photometer-controlled binocular stimulus fields and a central light system for fixation and variation of the contrast (background illumination). For exact binocular measurements of light sensitivity on both eyes, electronically controlled test fields (visual angle 5 degrees-20 degrees) guarantees only macular or overfoveolar stimulation. In addition, splitting the light for each stimulus field from only one halogen lamp guarantees wave-length-independent testing. Patients with various retinal diseases and neuritis nervi optici pathology were examined using pattern VEP, testing of the absolute lower threshold of light sensitivity, and binocular comparison over the range of luminous density. This binocular optical photometer system allowed minimal differences to be identified in the present visual function and after the eye had recovered from optic nerve neuritis.

Evoked Potentials, Visual↗
PubMed1999

Decision-related activity in the macaque dorsal visual pathway.

Brain areas at higher levels of cortical organization are thought to be more involved in decision processes than are earlier, i.e. lower, sensory areas. Hence, neuronal activity correlated with decisions should vary with an area's position in the cortical hierarchy. To test this proposal, we investigated whether a change in neuronal activity during error trials depends in a systematic way on cortical hierarchical position. While macaque monkeys discriminated the direction of moving visual stimuli, the activity of direction-selective neurons was recorded in four extrastriate visual areas: V3A, the middle temporal area, the middle superior temporal area and the posterior part of the superior temporal polysensory area. Neuronal activity was significantly reduced in all areas when the monkeys made errors in judging the direction of stimuli moving in the preferred direction with low and intermediate luminance contrast. The amount of activity reduction was approximately 50% in all of the visual areas. Thus, the activity on error trials is reduced in early visual processing, independent of the hierarchy in the dorsal visual pathway. The activity reduction depended on stimulus contrast and the direction of the decision relative to the stimulus motion. It was profound and significant in all areas at low stimulus contrast. However, it was nonsignificant at high stimulus contrast. Our data suggest that activity reduction on error trials is due to lack of attention in association with stimulus expectation.

Animals↗