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PubMed1992

[A case of the panencephalopathic type of Creutzfeldt-Jakob disease with retinal involvement].

Neuropathological study of the visual pathway from the retina to the occipital cortex in Creutzfeldt-Jakob disease (CJD) has been scarcely performed. In the present study, pathological involvement of the visual pathway was observed in a 54-year-old man with CJD. The patient had the onset of visual disturbances in December 1985. He subsequently developed progressive dementia, right hemiparesis, ataxia and dysarthria, and rapidly fell into decerebrate posture in February 1986. In March 1986, myoclonus appeared on the whole body and EEG revealed periodic synchronous discharges, while brain CT and CSF findings showed no abnormalities. Myoclonus was observed most frequently from May to October 1986, and then reduced gradually. Brain atrophy on CT started from April 1986, and was progressive till the end stage of the disease. He died in January 1988, and the total clinical course was about 24 months. Neuropathological examination revealed severe degeneration of the cerebral cortex and the white matter. In the cerebral cortex, marked loss of neurons, astrogliosis, and spongiform changes were observed. In the cerebral white matter, the destruction of myelin sheaths and axons were evident. The cerebellum showed prominent loss of granule cells. These findings are consistent with those of the panencephalopathic type of CJD. In the visual pathway, loss of ganglion cells and bipolar cells in the retina, mild demyelination of the optic nerve, neuronal loss in the lateral geniculate body, and severe degeneration in the visual cortex were observed. The present case suggests that the neuropathological investigation in the visual pathway from the retina to the occipital cortex is important for clarifying the pathological processes in the visual system in CJD.

Brain↗
PubMed2004

Retinol-binding protein gene is highly expressed in higher-order association areas of the primate neocortex.

The neocortex consists of histochemically, connectionally, and functionally distinguishable areas. Recently, molecular biological techniques have enabled us to find rare types of genes expressed in specific neocortical areas. We previously reported occ1 gene as preferentially expressed in the primary visual cortex (V1), using the differential display method. Here, by differential display, we found selective and strong expression of the serum retinol-binding protein (RBP) gene, in higher-order association areas. In V1, RBP mRNA was expressed only in the superficial part of layer II, but its expression increased, involving deeper layers, along the visual pathway. In visual association areas such as TE, RBP mRNA was strongly expressed in both supra- and infragranular layers. In primary auditory and somatosensory areas, as in V1, RBP expression was low, and restricted to the upper part of the supragranular layers. The laminar pattern of RBP expression is in marked contrast with that of occ1; and in early visual areas where both genes are expressed, these occur in distinct sublayers within the supragranular layers. In neonatal monkeys, the area-specific expression pattern of RBP was less distinct, suggesting that the characteristic expression of RBP in higher-order association areas is mainly established postnatally.

Animals↗
PubMed1991

Excitatory amino acid receptor-mediated transmission in geniculocortical and intracortical pathways within visual cortex.

1. A preparation of turtle (Chrysemys picta and Pseudemys scripta) brain in which the integrity of the intracortical and geniculocortical pathways in visual cortex are maintained in vitro has been used to differentiate the excitatory amino acid (EAA) receptor subtypes involved in geniculocortical and intracortical synapses. 2. Stimulation of the geniculocortical fibers at subcortical loci produces monosynaptic excitatory postsynaptic potentials (EPSPs) in visual cortical neurons. These EPSPs are blocked by the broad-spectrum EAA receptor antagonist kynurenate (1-2 mM) and the non-N-methyl-D-aspartate (NMDA) antagonist 6, 7-dinitroquinoxaline-2,3-dione (DNQX, 10 microM), but not by the NMDA antagonist D,L-2-amino-5-phosphonovalerate (D,L-AP-5, 100 microM). These results indicate that the geniculocortical EPSP is mediated by EAAs that access principally, if not exclusively, EAA receptors of the non-NMDA subtypes. 3. Stimulation of intracortical fibers evokes compound EPSPs that could be resolved into three components differing in latency to peak. The component with the shortest latency was not affected by any of the EAA-receptor antagonists tested. The second component, of intermediate latency, was blocked by kyurenate and DNQX but not by D,L-AP-5. The component of longest latency was blocked by kynurenate and D,L-AP-5, but not by DNQX. These results indicate that the compound intracortical EPSP is comprised of three pharmacologically distinct components that are mediated by an unknown receptor, by quisqualate/kainate, and by NMDA receptors, respectively. 4. Repetitive stimulation of intracortical pathways at 0.33 Hz produces a dramatic potentiation of the late, D,L-AP-5-sensitive component of the intracortical EPSP. 5. These experiments lead to a hypothesis about the subtypes of EAA receptors that are accessed by the geniculocortical and intracortical pathways within visual cortex.

2-Amino-5-phosphonovalerate↗
PubMed1993

Visual evoked potential characteristics and early diagnosis of Pelizaeus-Merzbacher disease.

OBJECTIVE: Early diagnosis of Pelizaeus-Merzbacher disease; assessment of disease progression. DESIGN: Pediatric neuro-ophthalmology evaluation of visual function with pattern and luminance visual evoked potentials; behavioral state assessment; electrophysiological diagnostic test; baseline estimates at the age of 11 weeks; 1-year follow-up. SETTING: University hospital electrodiagnostic vision research laboratory. PATIENTS CASE STUDY: X-linked Pelizaeus-Merzbacher disease; leukodystrophy; patient tested at the age of 11 weeks and at the age of 58 weeks for follow-up; five age-matched normal controls. INTERVENTIONS: Physical therapy, medication, evaluation. MAIN OUTCOME: Early diagnosis; diagnostic confirmation; objective monitor of disease progression. RESULTS: Abnormal spatial and temporal vision and abnormal visual pathway maturation; visual evoked potentials of proband with Pelizaeus-Merzbacher disease were grossly abnormal, reflecting myelination disorder. CONCLUSIONS: Visual evoked potential pediatric electrodiagnosis yields reliable measures of visual function and visual system maturation in leukodystrophy.

Behavior↗
PubMed2004

Regulation of retinal cone bipolar cell differentiation and photopic vision by the CVC homeobox gene Vsx1.

Cone bipolar cells of the vertebrate retina connect photoreceptors with ganglion cells to mediate photopic vision. Despite this important role, the mechanisms that regulate cone bipolar cell differentiation are poorly understood. VSX1 is a CVC domain homeoprotein specifically expressed in cone bipolar cells. To determine the function of VSX1, we generated Vsx1 mutant mice and found that Vsx1 mutant retinal cells form but do not differentiate a mature cone bipolar cell phenotype. Electrophysiological studies demonstrated that Vsx1 mutant mice have defects in their cone visual pathway, whereas the rod visual pathway was unaffected. Thus, Vsx1 is required for cone bipolar cell differentiation and regulates photopic vision perception.

Animals↗
PubMed1998

The ophthalmology of intracranial vascular abnormalities.

PURPOSE: To provide a practical review of the ophthalmologic manifestations of intracranial vascular abnormalities. METHODS: We reviewed ocular manifestations of the most common intracranial vascular abnormalities: intracranial aneurysms, carotid-cavernous fistulas, arteriovenous malformations, and cavernous malformations. RESULTS: Unruptured aneurysms can compress the third cranial nerve and the anterior visual pathways. Ruptured aneurysms and subarachnoid hemorrhage can result in Terson syndrome and papilledema. Direct and indirect carotid-cavernous fistulas most commonly cause the classic triad of proptosis, conjunctival chemosis, and cranial bruit but can masquerade as chronic conjunctivitis. Arteriovenous malformations, with or without hemorrhage, may compress portions of the retrochiasmal pathways, causing visual field loss. Cavernous malformations, when in the brainstem, commonly cause abnormalities of supranuclear, nuclear, and fascicular ocular motility. CONCLUSIONS: The ophthalmologist may be the first physician to encounter clinical manifestations of intracranial vascular abnormalities that may herald devastating neurologic complications. Prompt diagnosis facilitates appropriate management and therapy.

Adult↗
PubMedDate not supplied

Visual motion and cortical velocity.

Recent studies have revealed some remarkably simple relationships between visual performance and the neuroanatomy of the visual pathways. The visual field is mapped topographically on the surface of the striate cortex in man; the projection is large for the central visual field and is progressively compressed towards the periphery. Visual acuity decreases with distance from the fovea in proportion to the estimated cortical magnification factor, M (the extent of striate cortex in millimetres corresponding to a degree of arc in visual space). If a stimulus is magnified at peripheral locations in proportion to 1/M, it becomes equally resolvable across the visual field. This scaling procedure (M-scaling) maintains equivalence of the cortical projection of stimuli with different visual field loci. We have used M-scaling to investigate motion perception as a visual field variable. We report here that both the lower threshold of motion and adaptation to motion are uniform for M-scaled stimuli, and are related to the velocity of the 'cortical image'.

Humans↗
PubMed1987

[Refractive errors in visually handicapped children].

Aside from hereditary juvenile macular dystrophy (Stargardt's disease), the author observed a significant increase in the incidence of spheric and astigmatic refractive errors in a further six hereditary or congenital deformities with poor vision. A shift toward myopia was seen in cases of coloboma, both of the optic nerve head as well as of the macular region, and in cases of macular aplasia and hypoplasia. A shift toward hyperopia was found in complete and ocular albinism, in retinitis pigmentosa and congenital achromatopsia. This hyperopic shift is in contradiction to the hypothesis that myopia can be deprivation-induced. It is assumed that a disturbance of visual stimulation early in life can disrupt emmetropization and thus induce the eye to become either myopic or hyperopic, in combination with a high incidence of astigmatism. This disturbance of visual stimulation may be due to clouding of the dioptric media, though equally to congenital or hereditary defects in the retina or the visual pathways of visual cortex.

Adolescent↗
PubMed1997

Basal ganglia damage and impaired visual function in the newborn infant.

AIM: To examine the effects of early lesions in the visual pathway on visual function; and to identify early prognostic indicators of visual abnormalities. METHODS: The visual function of 37 infants with perinatal brain lesions on magnetic resonance imaging was assessed using behavioural and electrophysiological variables. RESULTS: Normal visual behaviour was observed in most infants with large bilateral occipital lesions, but all the infants with associated basal ganglia involvement had abnormal visual function. Visual abnormalities were also present in six infants with isolated basal ganglia lesions. CONCLUSIONS: These observations suggest that basal ganglia may have an integral role in human visual development and that their presence on neonatal MRI could be an early marker of abnormal visual function.

Basal Ganglia↗
PubMed2004

The role of spared calcarine cortex and lateral occipital cortex in the responses of human hemianopes to visual motion.

Some patients, who are rendered perimetrically blind in one hemifield by cortical lesions, nevertheless exhibit residual visual capacities within their field defects. The neural mechanism that mediates the residual visual responses has remained the topic of considerable debate. One explanation posits the subcortical visual pathways that bypass the primary visual cortex and innervate the extrastriate visual areas as the substrate that underlies the residual vision. The other explanation is that small islands of the primary visual cortex remain intact and provide the signals for residual vision. We have performed behavioral and functional magnetic resonance imaging experiments to investigate the validity of the two explanations of residual vision. Our behavioral experiments indicated that of the seven hemianopes tested, two had the ability to discriminate the direction of a drifting grating. This residual visual response was shown with fMRI to be the result of spared islands of calcarine cortical activity in one of the hemianopes, whereas only lateral occipital activity was documented in the other patient. These results indicate that the underlying neural correlates of residual vision can vary between patients. Moreover, our study emphasizes the necessity of ruling out the presence of islands of preserved function and primary visual cortex before assigning residual visual capacities to the properties of visual pathways that bypass the primary visual cortex.

Adult↗
PubMed2000

Visual search: bottom-up or top-down?

The aim of the experiments in this paper was to explore the relationship between top-down and bottom-up processes in visual search. Employing behavioral techniques, we first consider the possible role of the magnocellular visual pathway in visual search, and find that visual search does not necessarily depend on processing by this visual sub-system. We next use functional imaging (positron emission tomography) to explore the effect of varying top-down strategy during visual search. Our findings indicate that the neural processes underlying visual search are distributed over an extensive network of brain regions, with varying roles for different parts of the network as the dynamics of top-down vs. bottom-up influences shift. The conjunction of bottom-up processing with top-down attentional suppression of an irrelevant singleton could account for activity found in right primary visual cortex (V1). The conjunction of bottom-up processing with top-down attentional set could explain activity noted in the right superior temporal gyrus/insular cortex. The left lateral cerebellum appears to play a role in attention, either in signaling popout or in switching attention repeatedly between multiple visual attributes. Loci in left parietal cortex (parietal operculum/superior temporal gyrus, parieto-occipital fissure and precuneus) are implicated in attention-demanding search for a target shape. Returning to behavioral experiments, we find that, when multiple feature singletons compete for attention, interference between them is strongest for features closely related to the distinguishing target feature. This competition appears to be feature-level rather than object-level, and is characterized by a varying degree of specificity for different features. Task complexity modulates interference effects, even for abrupt visual onsets, which are often considered to capture attention involuntarily. Overall, our observations converge on the conclusion that visual search is extremely flexible and subject to considerable specificity of top-down control, although such specificity is clearly not absolute.

Adult↗
PubMed1998

[Visual information processing and the mechanism of vision. Clinical application].

Psychogenic disturbance of vision includes various abnormalities such as low vision, abnormal visual field, abnormal color sense and disturbance of binocular function, although there are no abnormalities either in the eyeball or optic nerve, and no organic changes in brain computed tomography (CT) or magnetic resonance imaging (MRI). To clarify these abnormalities, it is necessary first to study the mechanism of visual information processing. In this report, the mechanism of visual information processing such as visual acuity, visual field, vision and attention and binocular function was studied by standard electrophysiological methods as well as by new techniques including electroencephalography (EEG) topography, visual evoked response imaging system (VERIS), and magnetoencephalogram (MEG). The following four items and the possibilities for clinical application were studied and discussed. The subjects were normal adults and child volunteers, patients with disturbance of vision of psychogenic origin, and patients with abnormal visual fields caused by organic changes in the visual pathway. 1. Visual acuity (form vision). 1) Visually evoked potemtial (VEP), early receptor potential (ERP), and MEG examination were carried out for normal subjects and patients with psychogenic disturbance of vision. 2) The P 100 of pattern reversal VEP of the patients showed a significantly higher response. 3) In normal subjects, the P 300 was observed widely around the Pz in the ERPs during Landolt's ring stimulation. 4) In normal children, the P 300 was observed slightly temporal to the Pz. 5) In some patients maximum amplitude of P 300 was observed in the occipital or temporal region, but in other patients there was no P 300 response in any derivation. 6) MEG in patients with the conversion type of psychogenic disturbance of vision showed only 2 small dipolar patterns around 117 ms during flash stimulation. It was quite different from that of normal subjects. 2. Visual field. 1) Multifocal VEP using VERIS could detect experimental artificial hemianopia caused by conclusion of the half visual field in normal subjects. 2) Multifocal VEP could detect hemianopia or quadratanopia. 3) In multifocal VEP in normal subject, off-latency time was about 36 ms longer than on-latency time both in the center and at the periphery of the retina. The ratio of on/off response decreased from the center to the periphery. 4) In MEG using flash stimulation, hemianopia could be detected even in patients with fixation difficulties. 5) As the subjective visual field was not always in accord with the objective field, objective visual field evaluation is important. 3. Vision and attention. 1) To confirm the influence of attention on visual information processings in patients with disturbance of vision of psychogenic origin, a hypothetical 'island of attention' was postulated. 2) The 'spiral visual field' and the 'Inazuma-type visual field' could be explained by application of this hypothesis for patients with disturbance of vision. 3) Three kinds of waves in VEF, W 1, W 2, and W 3, were detected by MEG after the stimulation of line motion illusion. There was a tendency for the latency time on the attention side to be shorter than on the non-attention side in waves W 2 and W 3. 4) There was a tendency for the amplitude of the attention side to be higher than that of the non-attention side in wave W 3. 5) Attention may influence vision. 4. Binocular vision. 1) A stimulus target was devised which did not elicit N 75, P 100, or N 140 waves. When this target was used for stereoptic stimulation, a negative wave was elicited with a latency of 170 to 280 ms. 2) When the same stimulus target without parallax was used, this negative wave was elicited but the amplitude was small. 3) When evoked potentials were measured under the same conditions, an electric dipole was elicited from the occipital to the temporal region by the electric current source. (ABSTRACT TRUNCATED)

Adolescent↗
PubMed2001

Intracranial vascular abnormalities.

Intracranial vascular abnormalities such as intracranial aneurysms, carotid-cavernous fistulas, AVMs, and cavernous malformations commonly produce neuro-ophthalmologic symptoms and signs. Unruptured aneurysms can compress the third cranial nerve and anterior visual pathways. Subarachnoid hemorrhage from ruptured aneurysms can result in Terson's syndrome and papilledema. Direct and indirect carotid-cavernous fistulas most commonly cause the classic triad of proptosis, conjunctival chemosis, and cranial bruit but can masquerade as chronic conjunctivitis. AVMs, with or without hemorrhage, may compress portions of the retrochiasmal pathways, causing visual field loss. Cavernous malformations, when in the brainstem, commonly cause abnormalities of supranuclear, nuclear, and fascicular ocular motility. The ophthalmologist may be the first physician to encounter clinical manifestations of intracranial vascular abnormalities that may herald devastating neurologic complications. Prompt diagnosis facilitates appropriate management and therapy.

Eye Diseases↗
PubMed2003

Learning higher-order structures in natural images.

The theoretical principles that underlie the representation and computation of higher-order structure in natural images are poorly understood. Recently, there has been considerable interest in using information theoretic techniques, such as independent component analysis, to derive representations for natural images that are optimal in the sense of coding efficiency. Although these approaches have been successful in explaining properties of neural representations in the early visual pathway and visual cortex, because they are based on a linear model, the types of image structure that can be represented are very limited. Here, we present a hierarchical probabilistic model for learning higher-order statistical regularities in natural images. This non-linear model learns an efficient code that describes variations in the underlying probabilistic density. When applied to natural images the algorithm yields coarse-coded, sparse-distributed representations of abstract image properties such as object location, scale and texture. This model offers a novel description of higher-order image structure and could provide theoretical insight into the response properties and computational functions of lower level cortical visual areas.

Learning↗
PubMed1983

[Strabismus and amblyopia. Value of their early detection].

The authors emphasize the importance of the relations between strabismus and amblyopia. Strabismus is often the symptom which leads to the discovery of amblyopia. Amblyopia may cause strabismus, as in organic amblyopias induced by congenital lesions of the retina or visual pathways, and visual deprivation amblyopias due to corneal opacities and/or congenital cataracts. Unilateral clouding of normally transparent media (cornea, lens, vitreum) prevents normal stimulation of the retina which is necessary to the development of binocular vision. Anisometropic amblyopias also belong to this category. More often, amblyopia is the consequence of strabismus: it is then termed "functional strabismic amblyopia". Loss of the parallelism of the two visual axes disrupts the functional balance between the images received from the two eyes. The two images are different; one is suppressed. This suppression may eventually lead to amblyopia. Amblyopia was discovered in 593 of 1 757 studied cases of strabismus. Amblyopia was the cause of strabismus in 87 patients and was functional in the remaining 506. Among these latter, visual acuity was inferior or equal to 1/10 in 241 cases and between 2/10 and 7/10 in 265. 147 children in the first group and 136 in the second could be treated. Among these patients, who were treated before the age of seven, complete recovery was obtained in approximately 1/2 of cases and improvement in more than 1/4 of first group patients and 1/3 of second group patients. Results were all the better that treatment was initiated earlier and that patients were younger.(ABSTRACT TRUNCATED AT 250 WORDS)

Amblyopia↗
PubMed2000

Surgically created neural pathways mediate visual pattern discrimination.

Combined lesions of retinal targets and ascending auditory pathways can induce, in developing animals, permanent retinal projections to auditory thalamic nuclei and to visual thalamic nuclei that normally receive little direct retinal input. Neurons in the auditory cortex of such animals have visual response properties that resemble those of neurons in the primary visual cortex of normal animals. Therefore, we investigated the behavioral function of the surgically induced retino-thalamo-cortical pathways. We showed that both surgically induced pathways can mediate visually guided behaviors whose normal substrate, the pathway from the retina to the primary visual cortex via the primary thalamic visual nucleus, is missing.

Animals↗
PubMed2002

Responses of optokinetic neurons in the pretectum and accessory optic system of the pigeon to large-field plaids.

The accessory optic system and pretectum are highly conserved brainstem visual pathways that process the visual consequences of self-motion (i.e. optic flow) and generate the optokinetic response. Neurons in these nuclei have very large receptive fields in the contalateral eye, and exhibit direction-selectivity to large-field moving stimuli. Previous research on visual motion pathways in the geniculostriate system has employed "plaids" composed of two non-parallel sine-wave gratings to investigate the visual system's ability to detect the global direction of pattern motion as opposed to the direction of motion of the components within the plaids. In this study, using standard extracellular techniques, we recorded the responses of 47 neurons in the nucleus of the basal optic root of the accessory optic system and 49 cells in the pretectal nucleus lentiformis mesencephali of pigeons to large-field gratings and plaids. We found that most neurons were classified as pattern-selective (41-49%) whereas fewer were classified as component-selective (8-17%). There were no striking differences between nucleus of the basal optic root and lentiformis mesencephali neurons in this regard. These data indicate that most of the input to the optokinetic system is orientation-insensitive but a small proportion is orientation-selective. The implications for the connectivity of the motion processing system are discussed.

Animals↗
PubMed2000

Retinal ganglion cells regenerating through the peripheral nerve graft retain their electroretinographic responses and mediate light-induced behavior.

To assess the light-induced electrical activity of rodent retinal ganglion cells (RGCs) regenerating into a peripheral nerve (PN) graft we used non-invasive recording of electroretinographic responses to the contrast-reversal of sinusoidal gratings (p-ERG). On comparing the retinas that received a PN graft and retinas with only optic nerve (ON) transection, p-ERG responses were present in grafted retinas as late as 20 months after the surgery while they completely disappeared in non-transplanted controls within 4 months of ON transection. Next, the ability of regenerating RGCs to form functional connections with their targets in the superior colliculus (SC) was tested by a light-escape task. While the bilaterally blinded animals did not improve during the test, unilaterally grafted animals (with the contralateral eye blinded) reached 26% success in the last quartile of the light-escape task. This performance was significantly better than that of blind animals (ANOVA and Student-Newman-Keuls test; p<0.05), but did not reach the level of intact rats (87%). The transplanted rats, therefore, were capable of light perception, but at a sub-normal ability. In addition, we were also able to correlate the amplitude of the p-ERG response with the visual behavioral performance for each transplanted animal. This finding indicates that there is a direct link between the RGC electrophysiological activity and the functional capacity of the regenerated visual pathway. In conclusion, the above results indicate that (a) PN grafts help to preserve the normal electroretinographic activity of injured and regenerating RGCs (b) the regenerated visual pathway is functional and capable of mediating simple visual behavior and that (c) there is a correlation between the light-evoked RGC electrical activity and visual behavior and, finally, that (d) the effect of PN graft on the electrophysiological and functional restoration of the visual pathway is long-lasting or even permanent.

Animals↗