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 1,549 records · Page 86Linked to original sources
PubMed2004

Seasonal behavior in Drosophila melanogaster requires the photoreceptors, the circadian clock, and phospholipase C.

Drosophila melanogaster locomotor activity responds to different seasonal conditions by thermosensitive regulation of splicing of a 3' intron in the period mRNA transcript. Here we demonstrate that the control of locomotor patterns by this mechanism is primarily light-dependent at low temperatures. At warmer temperatures, when it is vitally important for the fly to avoid midday desiccation, more stringent regulation of splicing is observed, requiring the light input received through the visual system during the day and the circadian clock at night. During the course of this study, we observed that a mutation in the no-receptor-potential-A(P41) (norpA(P41)) gene, which encodes phospholipase-C, generated an extremely high level of 3' splicing. This cannot be explained simply by the mutation's effect on the visual pathway and suggests that norpA(P41) is directly involved in thermosensitivity.

Analysis of Variance↗
PubMed1981

Time of origin of neurons of the rat superior colliculus in relation to other components of the visual and visuomotor pathways.

Groups of pregnant rats were injected with two successive daily doses of 3H-thymidine from gestational day 12 and 13 (E12 + E13) until the day before parturition (E21 + 22) in order to label all the multiplying precursors of neurons. At 60 days of age the proportion of neurons generated (or no longer labelled) on specific days was determined in the separate layers of the superiorr colliculus. Neurogenesis begins with layers V and IV on day E12; the bulk (87%) of these cells are generated on day E13. This early-produced band of large neurons, the intermediate magnocellular zone, divides the superior colliculus into two cytogenetically distinct regions. In both the deep and the superficial superior colliculus neuron production is relatively protracted. In the deep superior colliculus neuron production peaks on day E15 in lay VII, on day E15 and E16 in lay VI, and on day E16 (the large neurons excluded) in layer V, indicating an inside-out sequence. In the superficial superio coliculus peak production time of both layer I and II is on day E16 but in the latter region neuron production is more prolonged and ends on day E18. One interpretation of these results is that the two pairs of superficial layers are produced in an outside-in sequence. These three cytogenetic subdivisions of the superior colliculus may be correlated with its structural-functional parcellation into an efferent spinotectal, a deep somatomotor and a superficial visual component. A comparison of neurogenesis in different components of the visuomotor and visual pathways of the rat indicates that the motor neurons of the extraocular muscles, the abducens, trochlear and oculomotor nuclei, and neurons of the nucleus of Darkschewitsch are produced first. Next in line are source neurons of efferents to the bulb and the spinal cord: those of the Edinger-Westphal nucleus and the intermediate magnocellular zone of the superior colliculus. These are followed by the relay neurons of the dorsal nucleus of the lateral geniculate body. The neurons of the superficial superior colliculus and of the visual cortex implicated in visual sensori-motor integrations are produced last.

Afferent Pathways↗
PubMed2003

Left and right occipital cortices differ in their response to spatial cueing.

We investigated cue and target-related laterality effects with event-related fMRI. Both left and right occipital areas responded maximally when both cue and target were presented in the contralateral visual hemifield (VF), and minimally when cue and target were presented in the ipsilateral VF. However, whereas signal increases in right ventromedial and lateral occipital cortex were intermediate in those trials in which the cue appeared in the VF contralateral to the target (invalid cue trials), signal strength in left occipital cortex was almost identical for valid and invalid cues, i.e., high for RVF cues, and low for LVF cues, independent of the VF of the target. These data support theories which postulate a greater ability of the right hemisphere for bilateral processing. However, these laterality effects were observed earlier in the visual pathway than previously thought, leading to the question whether the hemispheric differences observed in occipital cortex are generated in the activated areas or are the effect of reentrant processes from more anterior areas, potentially in parietal cortex.

Adult↗
PubMed2006

A neural model of the scintillating grid illusion: disinhibition and self-inhibition in early vision.

A stationary display of white discs positioned on intersecting gray bars on a dark background gives rise to a striking scintillating effect--the scintillating grid illusion. The spatial and temporal properties of the illusion are well known, but a neuronal-level explanation of the mechanism has not been fully investigated. Motivated by the neurophysiology of the Limulus retina, we propose disinhibition and self-inhibition as possible neural mechanisms that may give rise to the illusion. In this letter, a spatiotemporal model of the early visual pathway is derived that explicitly accounts for these two mechanisms. The model successfully predicted the change of strength in the illusion under various stimulus conditions, indicating that low-level mechanisms may well explain the scintillating effect in the illusion.

Action Potentials↗
PubMed1989

Bonnet syndrome and posterior parasagittal tumor: clues to neural mechanisms.

A case of Bonnet syndrome associated with blindness due to bilateral eye disease and a posterior parasagittal meningioma is reported. It is assumed that visual afferent deprivation alone is not enough to produce the syndrome and that, in most instances, a 'cerebral factor' must be operative if hallucinoses are to occur. The distinction between hallucinosis and hallucinations is favored and a common neural circuit for the mediation of hallucinotic imageries in general is suggested. One should not immediately put the blame on obvious eye or visual pathways affections when facing cases of Bonnet syndrome, as they are not likely to explain the complex array of images perceived by any given patient. On the contrary, the possibility of a clinically covert intracranial disease should be always raised and intensively looked for.

Aged↗
PubMedDate not supplied

Cerebral N-acetylaspartate is low in patients with multiple sclerosis and abnormal visual evoked potentials.

PURPOSE: Our purpose was to compare cerebral proton MR metabolite changes in patients with multiple sclerosis (MS) and abnormal visual evoked potentials (VEPs) with those in MS patients with normal VEPs. METHODS: Seventeen subjects with clinically definite MS were studied with VEPs and MR spectroscopic imaging. Proton MR metabolites were measured using a fast spectroscopic imaging technique called proton echo-planar spectroscopic imaging (PEPSI). Kurtzke's Expanded Disability Status Scale (EDSS) score was also ascertained for each subject to obtain a clinical rating. Twelve regions of interest within the visual pathway of the cerebrum were evaluated for levels of N-acetylaspartate (NAA), choline, creatine, and the presence or absence of MR-detectable lesions. RESULTS: PEPSI NAA values (water-normalized, CSF-corrected) were significantly lower in MS subjects with abnormal VEPs than in subjects with normal VEPs. MR-detectable lesion fractions and EDSS scores were also significantly different between the two VEP groups, but NAA comparison had a P value 100 times less than either of these measures. CONCLUSION: In patients with MS, NAA measurements in the optic pathways of the brain were sensitive to VEP abnormalities. NAA was more sensitive to VEP changes than were choline, creatine, MR-detectable lesions, and EDSS score.

Adult↗
PubMed1979

Neonatal suprachiasmatic nucleus lesions: effects on the development of circadian rhythms in the rat.

Previous studies of the effects of suprachiasmatic nucleus (SCN) destruction and visual pathway transections in adult rodents have revealed the primary significance of the SCN and the retinohypothalamic (RH) projection in the generation and entrainment of circadian rhythms. In the present study we found that complete ablation of the SCN in 2-day-old rats, prior to its innervation by the RH projection, permanently eliminates circadian rhythms in spontaneous locomotor activity and drinking; activity and drinking appear randomly distributed over the light-dark cycle. In addition, females exhibit long periods of constant vaginal cornification and an absence of normal estrous cycles. These effects are independent of the animal's visual status; that is, they occur in blinded as well as sighted animals. Incomplete SCN lesions results in partial disruption of rhythmic functions such as damping of circadian rhythms in activity and/or drinking, irregular estrous cycling, and/or complete disruption of only one or two of these measures of rhythmicity. The absence of spared functions after early SCN destruction is consistent with the high degree of specificity for the SCN exhibited by developing RH fibers and further emphasizes the significance of the SCN in circadian rhythm generation. Neither morphological nor functional plasticity has been found following neonatal ablation of the SCN in the rat.

Animals↗
PubMed1998

[Usefulness of multimodal evoked potentials and the electroretinogram in the early diagnosis of brain death].

INTRODUCTION AND METHODS: We studied 72 patients fulfilling all the criteria for brain death (BD) by means of a series of tests: brain stem auditory visual evoked potentials (VEP), short latent period somatosensory evoked potentials (SEV) and electroretinogram (ERG). RESULTS: Three characteristic PEATC patterns were identified: bilaterally flat (73.34%), bilateral I wave (16.66%) and unilateral I wave (10%). The N20 wave of the SEV and other later cortical components were not seen in any patients, whilst the so-called subcortical components were partially or totally maintained. The use of non-cephalic data permitted discussion as to the origin of the subcortical components. When cephalic data was used to obtain the ERG and the VEP, the a and b waves of the ERG were recorded in all cases, whilst in the VEP channel waves of inverse polarity appeared of similar morphology and the same latency, but of lower amplitude than those of ERG. When a non-cephalic reference was used, the morphology and latency of the ERG components were unchanged, whilst no response was obtained from the VEP channel. This electrophysiological pattern indicates that the only part of the visual pathway of patients with BD to maintain electrical activity is the retina. CONCLUSION: The application of this set of tests permits early diagnosis of BD, which is basic for transplantation.

Adolescent↗
PubMed1980

Albinism. Recent advances.

There have recently been several fundamental advances in our understanding of albinism, both in animals and in man. These advances have been in the division of oculocutaneous albinism into tyrosinase-negative and tyrosinase-positive forms, the demonstration of a widespread disturbance in the structure of melanosomes in X-linked ocular albinism, the description of the condition now known as autosomal recessive ocular albinism, and a peculair anatomical abnormality of the visual pathways which appears to be present in all forms of oculocutaneous and ocular albinism. Evidence has been presented which confirms that the retinogeniculate anomaly in human albinos is similar to that in animals, and it has recently been suggested that there may be two major patterns of geniculocortical projected in man, as there are in the Siamese cat.

Albinism↗
PubMed2001

Optic neuropathy and chiasmopathy in the diagnosis of systemic lupus erythematosus.

PURPOSE: To report the clinical presentation of acute visual loss in six patients who were ultimately diagnosed with systemic lupus erythematosus (SLE). METHODS: Retrospective case series. RESULTS: All patients had a positive antinuclear antibody and elevated anti-double stranded DNA titers. Five of six patients demonstrated gadolinium enhancement of the optic nerve and/or chiasm on magnetic resonance imaging (MRI). Most patients showed initial improvement after treatment with high-dose systemic corticosteroids, but five experienced recrudescences during steroid taper, requiring further treatment with immunosuppressive or cytotoxic medications. CONCLUSIONS: Visual loss owing to optic neuropathy or chiasmopathy may be the presenting sign of SLE or the event that leads to this diagnosis. Gadolinium-enhanced MRI is useful for identifying anterior visual pathway lesions in these patients. Corticosteroids are effective in the treatment of this condition; however, relapses requiring further treatment are common.

Adult↗
PubMed1987

Electrophysiological studies of the visual system in myotonic dystrophy.

Ocular signs and electroretinal alterations frequently occur in Myotonic Dystrophy (MD). Surprisingly few reports describe VEP abnormalities for this syndrome. Since the evaluation of cortical visual responses is linked to an understanding of preceding retinal changes, we conducted a systematic study of the visual system including ophthalmological and electrophysiological (EOG, ERG, PERG, VEP) investigation in 14 confirmed myotonic patients. The various tests revealed consistent abnormalities, the most frequent of these being PERG and VEP changes. These alterations seemed to occur independently of one another, suggesting impaired function at different levels of visual pathway. A generalized defect of cell membrane has recently been proposed as etiopathogenesis of typical EMG and systemic features of the disease. Such membrane dysfunction might account for the early and marked abnormalities in electrophysiological tests, even in the absence of neuro-ophthalmological changes.

Adult↗
PubMed1985

Acrylamide effects on the macaque visual system. II. Retinogeniculate morphology.

Oral acrylamide dosing for 6-10 weeks produced axonal swellings with neurofilament accumulation in the distal optic tract and lateral geniculate nucleus of macaques. No swellings were seen in the retina or optic nerve. Monkeys that were killed 6-8 months after similar dosing showed a marked neuronal degeneration in the visual pathways that was more pronounced after two than after a single period of exposure. This degeneration was characterized by the following: loss of ganglion cells in central retina with relative sparing of other retinal neurons; disproportionate degeneration of temporal to central optic nerve and the dorsal optic tract; and neuronal atrophy in parvocellular layers of the lateral geniculate nucleus, with relative sparing of magnocellular layers. The pattern of neuronal loss suggests that one type of retinal ganglion cell or its axon may be especially vulnerable to damage by acrylamide. The selective neuronal damage produced by acrylamide may help explain the nature of the visual dysfunction associated with this intoxication.

Acrylamide↗
PubMed2002

Sensory information processing in neuroleptic-naive first-episode schizophrenic patients: a functional magnetic resonance imaging study.

BACKGROUND: Schizophrenic disorders are thought to involve widespread abnormalities in information processing. The present study used functional magnetic resonance imaging and a simple and robust paradigm that involved auditory and visual activation to examine basic sensory input circuits. Our aim was to determine which stages of the input processing network are disturbed in first-episode schizophrenic patients. METHODS: Twelve neuroleptic-naive inpatients (paranoid subtype) were compared with 11 healthy subjects by means of echo-planar functional magnetic resonance imaging. In a block design, the paradigm included the simultaneous presentation of a moving 6-Hz checkerboard and auditory stimuli in the form of drumbeats. The subjects were asked to simply look and listen. RESULTS: In comparison with control subjects, patients showed reduced activation in the right thalamus, the right prefrontal cortex, and the parietal lobe (restricted to the dorsal visual pathway) bilaterally. There were no notable differences in the primary visual cortex or the object-specific occipitotemporal pathway. In addition, patients presented with a reduced signal change to auditory stimulation in the left acoustic cortex. CONCLUSIONS: The present study supports the concept of widespread cortical and subcortical deficits in schizophrenia. Our findings suggest abnormal functioning early in the information processing and in high-order association cortices already at illness onset, before the administration of medication or the most confounding effects of illness duration. The main regions have been implicated in visual motion perception and discrimination as well as in attention to sensorial events and perceptual synthesis.

Acoustic Stimulation↗
PubMed2000

A milestone for normal development of the infantile brain detected by functional MRI.

OBJECTIVE: To investigate the relationship between cerebral cortical function and white matter myelination in the visual pathway in the evaluation of normal brain development. METHODS: The authors performed quantitative analysis of white matter myelination detected with conventional T1-weighted spin echo (SE) MRI and brain functional MRI (fMRI) using echoplanar imaging with photic stimulation in 27 neurologically normal infants (age range, 0 to 22 weeks). RESULTS: An age-dependent gradual increase in signal intensity was observed in optic radiation on the T1-weighted SE images, indicating progression of white matter myelination. A rapid age-dependent reverse in signal response was observed on fMRI. Infants older than 8 weeks showed a stimulus-induced signal decrease in the visual cortex, whereas infants younger than 7 weeks showed a signal increase. CONCLUSIONS: A rapid inversion of response revealed by fMRI with photic stimulation in infants suggests a change in oxygen consumption during neuronal activation, which is related to rapid synapse formation and accompanying increased metabolism. fMRI can detect dynamic metabolic changes during brain maturation, which is a different developmental process from white matter myelination. The metabolic changes detected by fMRI provide a milestone for the evaluation of normal brain development.

Brain↗
PubMed1987

The role of medical imaging in the practice of neuro-ophthalmology.

The neuro-ophthalmologist is concerned with the myriad afflictions that can cause transient or permanent visual loss, derangement of ocular motor function, pupillary dysfunction, abnormality of lid position or function, and headache or facial pain syndrome. Once preliminary clinical evaluation has implicated dysfunction of a certain anatomic locale, the practitioner must precisely confirm or eliminate possible etiologies. This article examines pathology in six areas: orbital contents and optic nerve; cavernous sinus; chiasm; posterior visual pathway and cerebral cortex; brain stem and posterior fossa; and spinal cord. Through discussion of lesions in these areas the value of CT versus MR in making an accurate diagnosis is elucidated.

Brain Stem↗
PubMed1978

The transscleral VER: normal responses.

Normative data taken on a sample of 10 eyes indicate that transscleral visual evoked response (TVER) stimulation of the cortical evoked response with a range of lights and at lower adaptation levels produces replicable, low-variance responses which may be of sufficient quality for the clinical evaluation of retinal and visual pathway condition. Response amplitudes were related to the radiant peak-power of white stimuli but were greater for red stimuli. Attenuation of the subjective brightness of the stimulus delivered through the inferior lid and sclera was about 0.4 log units compared to corneal delivery. Typical signal:noise ratios were 5:1.

Adolescent↗
PubMed2005

Motion contrast classification is a linearly nonseparable problem.

Sensitivity to image motion contrast, that is, the relative motion between different parts of the visual field, is a common and computationally important property of many neurons in the visual pathways of vertebrates. Here we illustrate that, as a classification problem, motion contrast detection is linearly nonseparable. In order to do so, we prove a theorem stating a sufficient condition for linear nonseparability. We argue that nonlinear combinations of local measurements of velocity at different locations and times are needed in order to solve the motion contrast problem.

Animals↗
PubMed1997

Visual electrodiagnostic findings in mild traumatic brain injury.

Patients with traumatic brain injury (TBI) frequently exhibit varied forms of visual system dysfunction including: binocular, oculomotor, accommodative, refractive error shift, visual field loss, and visual perceptual deficits. A 5-year collaborative study between optometry and ophthalmology was initiated to follow documented mild TBI patients utilizing diagnostic methods to assess the quantity and quality of visual system deficits and recovery. A group of patients with mild TBI receiving optometric rehabilitation were compared with a group of age-matched, gender-matched, and headsize-matched TBI patients not receiving such treatment. Eighteen patients diagnosed with mild TBI underwent a treatment regimen of optometric rehabilitation (group I); 32 patients diagnosed with mild TBI did not receive optometric rehabilitation (group II). Pattern visually evoked cortical potential (VECP) testing and electroretinography (ERG) evaluation were utilized initially, repeated 6-12 months later and then 12-18 months after baseline. All TBI patients' VECP and ERG results were compared to age-matched, headsize-matched controls. Once the ERG had been used to exclude retinal involvement, identification of visual pathway dysfunction was possible with the VECP. Full-field ERG results in all groups were not remarkable and not sensitive for patients with mild TBI. Initial testing results revealed that 72% of those TBI patients in group I demonstrated VECP waveform abnormalities and 81% of those patients in group II showed waveform dysfunction. In the testing performed 12-18 months later, 38% of group I TBI patients, after receiving a treatment regimen of optometric rehabilitation, showed VECP waveform abnormalities; 78% of group II TBI patients demonstrated waveform abnormalities. VECP evaluation in patients with mild TBI can provide a useful and reliable tool for objective assessment of visual system deficit and recovery. Significant differences in visual system recovery were shown when comparing group I and group II.

Adolescent↗