Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Visual Pathways”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,027 records · Page 57Linked to original sources
PubMed2000

Vigabatrin-associated visual field defects in children.

PURPOSE: Vigabatrin (Sabril), a drug that blocks GABA transaminase, has been used in the treatment of epilepsy since 1989. There have been reports of irreversible constriction of the visual field in adult patients related to vigabatrin (VGB) therapy, resulting in reduced VGB usage in adults. Although used as a second or third line agent in adults, in children it is often considered as a first line treatment for several subgroups of seizures in spite of there being no way, in the majority of cases, to monitor visual fields. Some of these children have a pre-existing visual field defect as part of their primary disorder. We aimed to identify whether visual field loss due to VGB was occurring in our hospital. METHODS: We have studied the results of ophthalmic examination in 14 children on VGB at Great Ormond Street Hospital who were able to perform Goldmann visual fields. RESULTS: Ten of the 14 patients had constriction of their visual fields attributed to VGB. In addition there were 2 patients with suspicious visual field defects thought to be due to VGB. There was pre-existing visual pathway damage in 4 cases and in 2 of these optic disc pallor increased in association with constricted visual fields. However, the optic discs were normal in 7 patients in spite of visual field constriction. Visual acuity was generally normal in spite of gross visual field constriction. CONCLUSIONS: We believe that VGB should be used with great caution where there is pre-existing visual pathway damage. In other cases the benefits should be considered in relation to the risks, which include irreversible visual field damage. At present visual fields can only be monitored by perimetry, which is often not possible in children with epilepsy.

Adolescent↗
PubMed1990

Differences between ipsilaterally and contralaterally evoked potentials in the visual wulst of the zebra finch.

The telencephalic target of the thalamofugal visual pathway in birds, the visual wulst, is part of the hyperstriatum accessorium/dorsale in the bird's brain. In this study, we tried to determine the exact location of the visually responsive area in the zebra finch by recording visually evoked potentials (VEPs) from different sites throughout the hyperstriatum and calculating current source densities (CSDs). In addition, we examined the influence of ipsilateral and contralateral stimuli on stimulus processing within this area, and tried to get insight into the neuronal machinery of the thalamofugal pathway by application of drugs such as tetrodotoxin (TTX) and picrotoxin. About two-thirds of the hyperstriatum is responsive to contralateral stimuli but only a small portion responds to ipsilateral stimuli. Contralateral visual information arrives in the hyperstriatum dorsale (HD) and is processed further to the hyperstriatum accessorium (HA). The small influence of ipsilaterally evoked potentials is not due to inhibition by the activity of the contralateral eye, as could be demonstrated previously for the ectostriatum. Instead, our results show that ipsilaterally evoked potentials are inhibited at least in part by a projection from the contralateral visual wulst.

Animals↗
PubMed1999

Genetic disorders of vision revealed by a behavioral screen of 400 essential loci in zebrafish.

We examined optokinetic and optomotor responses of 450 zebrafish mutants, which were isolated previously based on defects in organ formation, tissue patterning, pigmentation, axon guidance, or other visible phenotypes. These strains carry single point mutations in >400 essential loci. We asked which fraction of the mutants develop blindness or other types of impairments specific to the visual system. Twelve mutants failed to respond in either one or both of our assays. Subsequent histological and electroretinographic analysis revealed unique deficits at various stages of the visual pathway, including lens degeneration (bumper), melanin deficiency (sandy), lack of ganglion cells (lakritz), ipsilateral misrouting of axons (belladonna), optic-nerve disorganization (grumpy and sleepy), inner nuclear layer or outer plexiform layer malfunction (noir, dropje, and possibly steifftier), and disruption of retinotectal impulse activity (macho and blumenkohl). Surprisingly, mutants with abnormally large or small eyes or severe wiring defects frequently exhibit no discernible behavioral deficits. In addition, we identified 13 blind mutants that display outer-retina dystrophy, making this syndrome the single-most common cause of inherited blindness in zebrafish. Our screen showed that a significant fraction (approximately 5%) of the essential loci also participate in visual functions but did not reveal any systematic genetic linkage to particular morphological traits. The mutations uncovered by our behavioral assays provide distinct entry points for the study of visual pathways and set the stage for a genetic dissection of vertebrate vision.

Albinism↗
PubMed1967

Spatial and temporal summation in impaired regions of the visual field.

1. Spatial and temporal summation have been measured in perimetrically impaired regions of the visual field. Two classes of impairment have been studied: that resulting from lesions in the pre-geniculate visual pathways, and that resulting from post-geniculate lesions (optic radiation and/or striate cortex).2. Control measurements were made in the perimetrically normal visual fields of subjects without visual pathway damage.3. Spatial summation was found altered in all impaired visual fields: the greater the threshold elevation produced by the lesion, the more nearly complete was spatial summation.4. The above relation between threshold and spatial summation has also been given numerical form. This has been shown to be very nearly identical to the threshold-spatial summation relation which is seen as stimuli are increasingly peripherally presented in normal visual fields.5. It has been shown that the alterations of spatial summation brought about by a lesion are found only in those parts of the visual field which are perimetrically impaired: spatial summation is always normal in perimetrically normal regions of a visual field, even if other parts of the same field show impairment.6. Temporal summation has been found altered in visual fields impaired by post-geniculate lesions: the greater the threshold elevation produced by the lesion, the more nearly complete was temporal summation. These changes in temporal summation were found only in perimetrically impaired regions of the field.7. Temporal summation was normal in visual fields impaired by pregeniculate lesions.

Geniculate Bodies↗
PubMed1980

Aberrant retinotectal pathways induced by larval unilateral optic nerve section in Xenopus.

Following unilateral optic nerve section in Xenopus tadpoles and toadlets, the reformation of visual pathways and retinotectal projections was analyzed using [3H]proline autoradiography. Bilateral retinotectal projections were found in 61% of the animals operated on between stages 42 and 58. In these animals, the projections were established through multiple aberrant pathways which included the oculomotor nerve, the trigeminal nerve and the posterior commissure. In contrast, in animals with optic nerve section at stage 62 or after metamorphosis, the regenerated optic fibres arrived at the contralateral and ipsilateral tecta through normal visual pathways.

Animals↗
PubMed1995

The brain's visual world: representation of visual targets in cerebral cortex.

Microelectrode recordings from behaving monkeys have shown that neuronal responses in the visual cerebral cortex can depend greatly on which aspect of the scene is the target of the animal's attention. Accumulating evidence suggests that while the early stages of the visual pathway provide a faithful representation of the retinal image, later stages of processing in the visual cortex hold representations that emphasize the viewer's current interest. By filtering out irrelevant signals and adding information about objects whose presence is remembered or inferred, the cortex creates an edited representation of the visual world that is dynamically modified to suit the immediate goals of the viewer.

Action Potentials↗
PubMed1999

The dynamic spatio-temporal behavior of visual responses in thalamus and cortex.

Due to eye and object movements the visual world changes on a rather fast time scale and the neuronal network of the primary visual pathway has to immediately react to these changes. Accordingly the neuronal activity patterns in the visual thalamus and cortex show a pronounced dynamic behavior which reenters the circuitry such that the actual cell responses are also guided by the activation history of the network. Thus, spatial and temporal aspects of visual receptive fields change not only by means of the actual visual stimulation hut also as a consequence of the state of the network. In this short review we summarize the different aspects which can influence the temporal firing patterns of cells in the visual thalamus (lateral geniculate nucleus, LGN) mainly by demonstrating how their inter-spike interval distributions will change. We then show that these firing patterns are able to change the spatial shape of receptive fields in the visual cortex (see Fig. 12 for a summary diagram). Finally, by means of a biophysical model, we will argue that the observed changes could serve to adjust the temporal and spatial resolution within the primary visual pathway to the different demands for information processing in an attentive as compared to a non-attentive state.

Journal Article↗
PubMed1993

Tenascin in the developing chick visual system: distribution and potential role as a modulator of retinal axon growth.

The distribution of the extracellular matrix protein tenascin was studied in the developing chick visual system to determine its possible regulatory role in retinotectal development. Little tenascin was present in the retinal optic fiber layer, and the optic nerve and tract, but was abundant in the stratum opticum of the tectum, the target of retinal axons in the brain. A high concentration of tenascin was found in areas bordering the developing visual pathway, such as the optic disc, the outer surface of the optic nerve, and the supraoptic commissure. In vitro studies showed that tenascin did not promote neurite outgrowth of retinal axons. When optic axons were confronted with a tenascin substrate in culture, they did not grow onto the tenascin suggesting that this protein inhibited optic axon outgrowth. Furthermore, the addition of tenascin to retinal explants in collagen gels slowed the growth rate of optic axons by as much as 50%. The distribution of tenascin in vivo and its inhibitory function in several in vitro systems suggest that this protein acts as a modulator of axonal growth in vivo. Tenascin may act as a barrier at specific sites along the visual pathway, and at the target, may slow the rate of axon outgrowth, and ultimately act as a stop molecule. The growth inhibitory activity of tenascin in retinal and tectal synaptic layers may also serve to stabilize synapses once appropriate connections have been made.

Animals↗
PubMed1992

The fourth C.U. Ariëns Kappers lecture. The organization of the human circadian timing system.

The mammalian circadian timing system has three principal components; (1) photoreceptors and visual pathways mediating entrainment; (2) a pacemaker, the suprachiasmatic nucleus of the hypothalamus; and (3) efferent pathways coupling the suprachiasmatic nucleus to effector systems exhibiting circadian function. In most mammals there are two visual entraining pathways, a direct retinohypothalamic pathway terminating in the suprachiasmatic nucleus, for which the transmitter is unknown, and a secondary visual pathway, the geniculohypothalamic tract, from the intergeniculate leaflet of the lateral geniculate to the suprachiasmatic nucleus that is neuropeptide Y-producing. These pathways end in a distinct subdivision of the suprachiasmatic nucleus characterized by the presence of vasoactive intestinal polypeptide neurons. A second suprachiasmatic nucleus division does not receive visual afferents and is characterized by vasopressin neurons. The efferent projections of the suprachiasmatic nucleus are very restricted, predominantly to the hypothalamus. Although we have much less information on the human circadian timing system than on that of other animals, it seems clear that the human conforms to the general animal pattern in most features. There are, however, two significant differences. First, the largest neural component of the human suprachiasmatic nucleus is a population of neurotensin neurons found throughout the nucleus. Few, if any, neurotensin neurons are found in monkey or other mammals. Second, the human suprachiasmatic nucleus contains a large number of neuropeptide Y neurons located where the plexus arising from geniculate neuropeptide Y neurons is found in other mammals. This is unique and suggests that the geniculohypothalamic projection may be bypassed in the human. It also may imply that the functional organization of the human SCN is fundamentally different from that of other mammals. The function of the circadian timing system is to coordinate the activities of a series of homeostatic regulatory mechanisms with the control of behavioral state in a temporal pattern that facilitates adaptive behavior, including reproduction (Fig. 9). The function of this system, then, is to provide the appropriate physiological and behavioral background to facilitate adaptation and survival.

Animals↗
PubMed2002

Descending pathways controlling visually guided updating of reaching in cats.

This study uses a previously described paradigm (Pettersson et al., 1997) to investigate the ability of cats to change the direction of ongoing reaching when the target is shifted sideways; the effect on the switching latency of spinal cord lesions was investigated. Large ventral lesions transecting the ventral funicle and the ventral half of the lateral funicle gave a 20-30 ms latency prolongation of switching in the medial (right) direction, but less prolongation of switching directed laterally (left), and in one cat the latencies of switching directed laterally were unchanged. It may be inferred that the command for switching in the lateral direction can be mediated by the dorsally located cortico- and rubrospinal tracts whereas the command for short-latency switching in the medial direction is mediated by ventral pathways. A restricted ventral lesion transecting the tectospinal pathway did not change the switching latency. Comparison of different ventral lesions revealed prolongation of the latency if the lesion included a region extending dorsally along the ventral horn and from there ventrally as a vertical strip, so it may be postulated that the command for fast switching, directed medially, is mediated by a reticulospinal pathway within this location. A hypothesis is forwarded suggesting that the visual control is exerted via ponto-cerebellar pathways.

Animals↗
PubMed2000

Impaired behavioral suppression by light in metabotropic glutamate receptor subtype 6-deficient mice.

The metabotropic glutamate receptor subtype 6 is localized on the dendrites of ON bipolar cells in mammalian retina, and is responsible for synaptic transmission from photoreceptors to ON bipolar cells. We have previously provided electrophysiological evidence that metabotropic glutmate receptor subtype 6-deficient mice have an impairment in the ON visual pathway. In this study, we compared, between metabotropic glutamate receptor subtype 6-deficient (n=9) and wild-type mice (n=7), their daily wheel-running activity in constant dark and light-dark cycle environments. There was no difference in their free-running rhythmicity in a constant dark environment nor in their ability to entrain their active/rest phase to the phase-shifted light-dark cycle environment, indicating that the circadian system in mutant mice was functioning normally. However, the wheel-running activity was suppressed immediately after light onset of the light-dark cycle in wild-type mice (suppressive effect), whereas that of mutant mice was prolonged for several hours in spite of light onset (very weak suppressive effect). The suppression of activity in wild-type mice is a "masking effect" of the endogenous circadian rhythm in response to light stimuli. The results indicate that the failure of mutant mice to suppress their activity upon light onset is not due to abnormality in their circadian system, but to their lack of response to light stimuli. This study clearly demonstrates that the dysfunction of the ON visual pathway in metabotropic glutamate receptor subtype 6-deficient mice impairs their behavioral responsiveness to light and yet preserves their circadian system.

Animals↗
PubMed1987

Retinal decussation patterns in pigmented and albino ferrets.

The decussation patterns of retinal ganglion cells in adult pigmented and albino ferrets were determined from the distribution of cells labelled after large unilateral injections of horseradish peroxidase into the visual pathway, involving the lateral geniculate nucleus and fibres of passage to the superior colliculus. About 6000 retinal ganglion cells project ipsilaterally in pigmented ferrets compared with only about 1500 in albino ferrets. In both strains, the vast majority of these cells (99 and 87% in pigmented and albino animals, respectively) are located in the temporal crescent, although we describe one albino ferret in which an aberrant uncrossed projection arises from nasal retina. In pigmented ferrets, there is a sharp nasotemporal division that runs through the area centralis; a small proportion of the ganglion cells in temporal crescent (less than 10%) does project contralaterally. In albinos, however, the majority of cells in temporal retina project contralaterally. There is no clear nasotemporal division in the albino retina; the density of uncrossed ganglion cells is reduced throughout temporal crescent and at no location exceeds the comparable density of the crossed projection. The peak density within the reduced uncrossed projection is also displaced away from the area centralis into temporal retina. Analysis of cell type on the basis of soma size indicates that whereas large horseradish peroxidase injections into the visual pathway of pigmented ferrets label all types of ganglion cell in the crossed projection, injections restricted to the superior colliculus label only those ganglion cells with large or small somata. The distribution of cell sizes in the crossed projection from temporal retina is biased towards small cells in the pigmented ferret but in albinos resembles that seen in the crossed projection from nasal retina. Thus the adult pigmented ferret has both a well developed nasotemporal division in which decussation lines are obvious in the crossed and uncrossed pathways and also, unlike rodents but like cats, a class of ganglion cell that does not project to the superior colliculus. The albino mutation both reduces the uncrossed projection throughout temporal retina, although the reduction is greatest close to the area centralis, and also commensurately increases the crossed projection from temporal retina.

Albinism↗
PubMedDate not supplied

Sensitivity and specificity of new eye check chart for neuro-ophthalmological diseases.

PURPOSE: To determine the sensitivity and specificity of a new Eye Check Chart (ECC) for screening neuro-ophthalmological patients with lesions in the visual pathways. METHODS: The Humphrey perimeter (HP) with the 30-2 SITA Fast program was used to confirm the visual field defects found in 65 eyes of 35 neuro-ophthalmological patients. Forty eyes had pregeniculate lesions, and 25 eyes had postgeniculate lesions. As controls, 22 eyes of 12 patients without visual field defects were also examined. All subjects were then examined using the eye check chart (ECC) to determine whether comparable visual field defects were detected. The eyes were separated into those in which the ECC findings agreed with the HP findings, and those in which they did not agree. Based on HP results, the sensitivity and specificity of the ECC results were calculated. RESULTS: The sensitivity of ECC was 87% in patients with pregeniculate lesions and 80% in patients with postgeniculate lesions. The overall specificity of ECC was 91%. CONCLUSION: This high sensitivity and specificity indicate that ECC can give reliable results in screening neuro-ophthalmological patients for lesions in the visual pathways.

Adult↗
PubMed2001

Sound alters visual evoked potentials in humans.

When a single flash is accompanied by two auditory beeps, the single flash is perceived as two flashes. We investigated whether this crossmodal influence on visual perception occurs at the level of the modality-specific visual pathway or later. We compared the visual evoked potentials (VEPs) in the presence and absence of sound. Activity was modulated extensively and with short latency in trials in which an illusory flash was perceived. In addition, the brain potentials for the illusory flash were qualitatively very similar to those for a physical flash, suggesting that the same mechanism underlies the percept of both illusory and physical flashes. These results suggest that the activity in the visual cortex can be modulated by sound. This implication challenges the general belief that the visual cortical processing is independent of other modalities.

Acoustic Stimulation↗
PubMed2002

[Visual representation for object recognition and visuomotor control: an evaluation using two orientation matching tasks].

This study examined effects of binocular information on visual orientation perception and visuomotor control of a hand using two tasks in which observers matched the orientation of two rods. On the perceptual matching task, they were asked to make a visual judgment of the orientation of two rods. On the motor (preshaping) task, they were asked to move a rod which they can not see by their hands so as to match the orientation of the presented rod. Decrement in availability of binocular cues produced considerable disruptions on the motor task, while did less disruptions on the perceptual matching task. Hence binocular information seemed to play a critical role on the motor task. These results are consistent with recent suggestions that visual perception and visually guided motor control should be mediated by separate visual pathways.

Adult↗
PubMed1995

The McCollough effect reveals orientation discrimination in a case of cortical blindness.

BACKGROUND: The McCollough effect is a colour after-effect that is contingent on the orientation of the patterns used to induce it. To produce the effect, two differently oriented grating patterns--such as a red-and-black vertical grating and a green-and-black horizontal grating--are viewed alternatively for a few minutes. After this period of adaptation, if the black-and-white test gratings are viewed in the same orientation as the adaptation patterns, the white sections of the vertical grating will appear pale green and the white sections of the horizontal grating will appear pink. The McCollough effect indicates that colour- and orientation-coding mechanisms interact at some point during visual processing; but the question remains as to whether this interaction occurs at an early or later stage in the cortical visual pathways. In an attempt to answer this question, we studied a patient who had suffered extensive damage to extrastriate visual areas of the brain, which had left him able to see colour but little else. RESULTS: Neuropsychological and perceptual tests demonstrated that the patient, P.B., has a profound impairment in form perception and is even unable to discriminate between 90 degrees differences in the orientation of grating stimuli. He is also unable to use orientation information to control his reaching or grasping. Nevertheless, P.B. can name and discriminate different colours reliably, including those used to induce the McCollough effect. After adaptation with red-and-green gratings, P.B. appropriately reported the orientation-contingent aftereffect colours, even though he continued to be unable to discriminate the orientations of the test patterns. CONCLUSIONS: These results indicate that at some level in P.B.'s visual system orientation is being coded, but it is at a level that he is unable to use in making orientation judgements or in visuomotor control. Given the massive insult to the extrastriate cortex in P.B., it is likely that the anatomical locus of the mechanisms underlying the McCollough effect is within primary visual cortex or even earlier in the visual pathway.

Adult↗
PubMed1997

Pattern reversal visual evoked potentials in classic and common migraine.

Pattern reversal visual evoked potentials (PVEPs) to transient checkerboard were recorded in 19 patients with migraine with visual aura (i.e., classic migraine), 14 patients with migraine without aura (i.e., common migraine) in the interictal period and 43 normal subjects. Latencies and amplitudes of PVEPs in each group were analyzed. In classic migraine patients, P100 amplitude was significantly higher than in normal subjects (p < 0.01), whereas latencies of PVEPs did not significantly differ. There were no significant differences between the common migraine and normal subjects, nor within the classic and common migraine groups in latencies and amplitudes of PVEP. Four patients with classic migraine underwent PVEPs during or 1-2 h immediately after their migraine attacks. Two of these patients who underwent PVEPs 1.5-2 h after their attacks showed abnormally increased PVEP amplitudes. These results suggest that there are different pathophysiologies in the visual pathway between classic and common migraine and furthermore, classic migraine patients in interictal periods may have hyperexcitability in the visual pathway and that the increased amplitude of PVEPs after attacks may be due to cortical spreading depression.

Adolescent↗
PubMed2002

Flash visual evoked potentials in the hypomyelinated mutant mouse shiverer.

Myelin basic protein (MBP) is an essential component of central nervous system (CNS) myelin, as demonstrated by shiverer mutant mice that have deletions of most of the Mbp structural gene. These mutants do not produce detectable MBP protein, and their CNS is hypomyelinated. Although the function of the visual pathway is presumed to be adversely affected by hypomyelination of the optic nerve, it has never been studied. We compared flash visual evoked potentials (FVEPs) of shiverer homozygotes with those of their wild-type littermates in order to characterize any dysfunction. There was a statistically significant delay in the implicit times of a negative component peaking at 85 ms and a large positive component peaking at 170 ms in the FVEPs of the shiverer mice. The amplitudes of the two components did not differ significantly in the shiverers and wild-type controls. Barring a retinal pathology, which cannot be excluded by these data, the delayed FVEP of the shiverer can likely be attributed to effects of hypomyelination of the optic nerve, optic tract and visual radiations on conduction time in the visual pathway and subsequent further post-synaptic delays.

Animals↗