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At least 559 records · Page 31Linked to original sources
PubMed1979

Correlation of CAT scan and visual field defects in vascular lesions of the posterior visual pathways.

Thirty-nine patients with various types of isolated homonymous hemianopias resulting from ischaemic lesions in the posterior parts of the cerebral hemisphere was examined by CAT scanning. Most had localised low density lesions withing the distribution of the posterior cerebral artery. The location of the lesion (deduced from a separate anatomical study of postmortem brain cut in the plane of the CAT scanner) was correlated with visual field defects. Lesions giving rise to quadrantic defects were smaller than those causing total hemianopias; lower quadrantic defects tended to occur in superior cuts and vice versa. Macular sparing was associated with survival of the occipital pole in some instances. Bilateral cases had a higher prevalence of associated defects.

Adult↗
PubMed1996

[Vision disorders in retrochiasmatic lesions of the visual pathways].

Anatomic elements of the retrochiasmatic pathway. Synopsis of homonymous pathway. Synopsis of homonymous hemianopia: unilateral forms [quadrant, total], bilateral forms [tunnel field, cerebral blindness], homonymous scotomas, horizontal hemianopsias, checkerboard hemianopsias, sparing of temporal crescent. Additional disorders: hemi-neglect, color agnosia, hemi-achromatopsia, alexia, abnormal optokinetic nystagmus, cog-wheel pursuit movement, hemianopic pupillary defect, statokinetic dissociation [Riddoch phenomenon], hallucinations, illusions, visual agnosia, prosopagnosia.

Aged↗
PubMed1988

The flight of colours test. Its value as an indicator of dysfunction of the visual pathways.

The flight of colours (FOC) test was compared with visual evoked potentials (VEPs) in 135 patients in a 2 year prospective study, to determine whether the FOC test is a sensitive and reliable alternative. We obtained an 80% overall agreement between the tests, confirming the levels of agreement reported by Rolak (87%) and Swart and Millac (92%). Abnormal VEPs, however, were more closely associated with cases of clinically definite multiple sclerosis (MS) while abnormal FOCs were more frequent in cases of non-demyelinating disease and cases without clinically evident optic nerve or other ocular disorder. We cannot explain this result by any demonstrated superiority of the FOC test over VEPs in non-demyelinating visual disturbances, whether clinically evident or not. Thus the study does not confirm the earlier expectation that the FOC test would be a reliable alternative to the study of VEPs in the differential diagnosis of MS.

Adolescent↗
PubMed1994

Aberrant visual pathways in microphthalmic mice.

We report results obtained in the microphthalmic strain of mice 944. Heterozygotes appear normal, but they produce litters in which typically between 2 and 5 offspring exhibit microphthalmia. As a result these animals are blind. Our investigations using the fluorescent tracer DiI show that in microphthalmic mice there is a small compensation for the missing retinal input by terminals or axon collaterals originating in the somatosensory thalamus. These morphological findings agree with somatosensory responses recorded in the visual cortex (EEG recordings).

Animals↗
PubMed1992

Structural modeling of functional visual pathways mapped with 2-deoxyglucose: effects of patterned light and footshock.

This paper describes the first application of structural modeling to the visual system. Structural modeling, or path analysis, is a mathematical method that allows for the quantification of the functional strengths of anatomical connections between the structures that form a neural system. The objective was to demonstrate how structural modeling can be used to determine the functional interrelationships between brain structures that form the visual system and how these interrelationships change under different conditions. Data were obtained from measures of 2-deoxyglucose uptake in the visual system of rats presented with either patterned light or darkness. The effects of arousing footshock on visual system operations were also investigated. Models based on the anatomical connections and the interregional correlations between metabolic activity data were used to determine path coefficients representing the magnitude of the influence of each directional path. Statistical evaluation of the models revealed that the dominant positive influences on visual system activity in the darkness were the tectocortical subsystem and the descending connections from secondary visual cortex. In the patterned light model, the total influence of the geniculocortical subsystem was higher than in the dark, and the tectocortical pathways showed both a reduction and a shift in the direction of effects. The models also revealed that the effects of footshock-induced arousal on visual system operations depended upon the visual environment and on extra-visual influences. The footshock led to an increase in the interaction of the two main subsystems at the level of connections between primary visual cortex and the lateral posterior nucleus, and a descending negative influence from the secondary visual cortex became dominant. The models are discussed in the context of conventional analyses to show how structural modeling allows for the determination of much more information about the functional interactions within the visual system of subjects under different experimental conditions.

Animals↗
PubMed1986

Abnormalities of the central visual pathways in Prader-Willi syndrome associated with hypopigmentation.

Patients with oculocutaneous or ocular albinism have misrouting of optic fibers, with fibers from 20 degrees or more of the temporal retina crossing at the chiasm instead of projecting to the ipsilateral hemisphere. Misrouting can result in strabismus and nystagmus. Because patients with the Prader-Willi syndrome may also have hypopigmentation and strabismus, we wondered whether they too might have misrouting of optic fibers. We therefore studied six patients with Prader-Willi syndrome selected for a history of strabismus, using pattern-onset visually evoked potentials with binocular and monocular stimulation to look for evidence of misrouted retinal-ganglion fibers. Four had hypopigmentation, and three of these four had abnormal evoked potentials indistinguishable from those recorded in human albinos. The two with normal pigmentation had normal responses. These findings indicate that patients with Prader-Willi syndrome who have hypopigmentation have a brain abnormality characterized by misrouting of retinal-ganglion fibers at the optic chiasm--a finding previously reported only in forms of albinism.

Adult↗
PubMed1995

Scotoma perception in white-noise-field campimetry and postchiasmal visual pathway lesions.

The authors examined 59 patients (32 women and 27 men) suffering from homonymous hemianopia by white-noise-field campimetry (Tübingen Electronic Campimeter) and by conventional perimetry (Tübingen Automatic Perimeter or Tübingen Manual Perimeter) and by computerized tomography (CT) or magnetic resonance imaging (MR). In all, 56 patients showed neuroradiologically detectable cerebral lesions, which were superimposed in a reconstructed "reference brain". Of these 56 patients, 18 were not capable of perceiving any white-noise-field scotoma, although their conventional perimetric findings showed defects. Lesions of these patients were concentrated along the optic radiation and spared the primary visual cortex. The lesions of the remaining 38 patients with scotoma detectable in both methods were accumulated in area V1, the primary visual cortex. The lesions of 6 patients, who had had persistent scotoma perception for more than 2 years, were situated at the occipital pole. The lesions of 8 patients with vanishing scotoma were concentrated in more rostral areas.

Adolescent↗
PubMed2001

Chattering and differential signal processing in identified motion-sensitive neurons of parallel visual pathways in the chick tectum.

At least three identified cell types in the stratum griseum centrale (SGC) of the chick optic tectum mediate separate pathways from the retina to different subdivisions of the thalamic nucleus rotundus. Two of these, SGC type I and type II, constitute the major direct inputs to rotundal subdivisions that process various aspects of visual information, e.g., motion and luminance changes. Here, we examined the responses of these cell types to somatic current injection and synaptic input. We used a brain slice preparation of the chick tectum and applied whole-cell patch recordings, restricted electrical stimulation of dendritic endings, and subsequent labeling with biocytin. Type I neurons responded with regular sequences of bursts ("chattering") to depolarizing current injection. Electrical stimulation of retinal afferents evoked a sharp-onset EPSP/burst response that was blocked with CNQX. The sharp-onset EPSP/burst response to synaptic stimulation persisted when the soma was hyperpolarized, thus suggesting the presence of dendritic spike generation. In contrast, the type II neurons responded to depolarizing current injection solely with an irregular sequence of individual spikes. Electrical stimulation of retinal afferents led to slow and long-lasting EPSPs that gave rise to one or several action potentials. In conclusion, the morphological distinct SGC type I and II neurons also have different response properties to retinal inputs. This difference is likely to have functional significance for the differential processing of visual information in the separate pathways from the retina to different subdivisions of the thalamic nucleus rotundus.

Action Potentials↗
PubMed1985

An underestimated visual pathway in reptiles.

Field potentials evoked in the turtle general cortex by electric stimulation of the optic tectum were analyzed. Cathodal polarization and subtotal lesions of n. rotundus led to either facilitation or depression of later components of the cortical potential. On the contrary, cathodal polarization and lesions of n.geniculatus lateralis dorsalis similarly affected the initial component. After 21-23 months following eye enucleation or optic nerve section, the conduction of fast tectal volleys to the general cortex via n. geniculatus lateralis dorsalis was blocked, though the conduction of tectal impulses to the dorsal ventricular ridge via n.rotundus survived. It is concluded that in turtles one more visual channel, i.e., retino-tecto-geniculo-cortical, is functioning, in addition to well-known retino-tecto-rotundo-telencephalic and retino-geniculo-cortical channels.

Animals↗
PubMed1988

Transformations of the retinal topography along the visual pathway of the chicken.

It is still unclear how the retinotectal map of the chick is formed during development. In particular, it is not yet known whether or not the organization of fibres plays a role in the formation of this map. In order to contribute to the solution of this problem, we analysed the representation of the retinal topography at closely spaced intervals along the fibre pathway. We injected HRP into various sites of the tectal surface and traced the labelled fibre bundles back to the retina. The retinal topography was reconstructed at ten different levels, i.e. in the retina, the optic nerve head, the middle of the optic nerve, the chiasm (three levels), the optic tract (three levels), and the optic tectum. We obtained the following results: (1) The labelled fibre bundles as well as the fields of labelled retinal ganglion cells were always well delimited and coherent. (2) The reconstructions show that transformations of the retinal topography occur in the fibre pathway. The first and most important transformation is found in the optic nerve head where the retinal image is mirrored across an axis extending from dorsotemporal to ventronasal retina. In addition, the retinal representation is split in its temporal periphery. Thus, central and centrotemporal fibres are no longer in the centre of the image but close to the dorsal border of the nerve. Peripheral fibres are found along the medial, ventral and lateral circumference of the nerve. In the optic tract a second transformation occurs. The retinal topography is rotated clockwise by about 90 degrees and flattened to a band. The flattening is accompanied by a segregation of fibre bundles so that eventually central and centrotemporal retinal fibres are located centrally, ventral fibres dorsally and dorsal retinal fibres ventrally in the tract. By these two transformations an organization of fibres is produced in the optic tract which can be projected onto the tectal surface without major changes given that dorsal and ventral fibres remain in their relative positions, and that deep lying fibres project to the rostral and central tectum, superficial fibres to the caudal tectum. The transformations which we have observed follow specific rules and thus maintain order in the pathway although retinotopy is lost. In conjunction with our earlier studies on the development of the retinotectal system we conclude that fibres are laid down in a chronotopic order. The transformations take place under particular structural constraints.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗