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Results for “Vision, Monocular”

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At least 271 records · Page 15Linked to original sources

PubMed2006

Visual deprivation reactivates rapid ocular dominance plasticity in adult visual cortex.

Brief monocular deprivation (< or =3 d) induces a rapid shift in the ocular dominance of binocular neurons in the juvenile rodent visual cortex but is ineffective in adults. Here, we report that persistent, rapid, juvenile-like ocular dominance plasticity can be reactivated in adult rodent visual cortex when monocular deprivation is preceded by visual deprivation. Ocular dominance shifts in visually deprived adults are caused by a rapid depression of the response to stimulation of the deprived eye, previously only reported in juveniles, and a simultaneous potentiation of the response to stimulation of the nondeprived eye. The enhanced ocular dominance plasticity induced by visual deprivation persists for days, even if binocular vision precedes monocular deprivation. Visual deprivation also induces a significant decrease in the level of GABAA receptors relative to AMPA receptors and a return to the juvenile form of NMDA receptors in the visual cortex, two molecular changes that we propose enable the persistent reactivation of rapid ocular dominance plasticity.

Age Factors↗

PubMed1995

Expression of DMAP-45R in the rat visual cortex is modulated by visual experience.

Effects of visual experience upon expression of a developmentally regulated microtubule-associated protein (MAP) were studied in the visual cortex of monocularly deprived rats. The antibody Drosophila MAP-45 (DMAP-45) recognizes proteins in the developing ventral nerve cord of Drosophila and in rat brain. Monocular deprivation from day 12, before eye opening, to day 80 reduced the number of DMAP-45 immunoreactive layer V pyramidal cell apical dendrites in the monocular segment (Oc1M) of the visual cortex contralateral to the deprived eye. No significant visual deprivation effects were seen in the binocular segment (Oc1B). Immunoreactivity was restored to control levels in Oc1M of rats in which the monocular sutures were removed at day 75, subsequently allowing 5 days of exposure to light. These results indicate potential involvement of this MAP in experience-dependent structural plasticity.

Animals↗

PubMed1974

Monocularly deprived cats: improvement of the deprived eye's vision by visual decortication.

Monocularly deprived cats were tested for visual perinetry before and after visual cortex lesions. Such a lesion greatly enhances the deprived eye's performance and impairs that of the nondeprived eye so that the pronounced preoperative interocular asymmetry is lost postoperatively. Apparently this destruction of abnormal corticotectal pathways allows the expression of previously suppressed, normal retinotectal pathways.

Animals↗

PubMed1998

Visual system maldevelopment disrupts extraocular muscle-specific myosin expression.

The genetic and epigenetic influences that are responsible for the establishment and maintenance of the unique phenotype of the extraocular muscles (EOMs) are poorly understood. A role for visual cues in shaping EOM maturation was assessed in rats by using two visual deprivation paradigms, dark rearing and monocular deprivation. Isoforms of the contractile protein myosin heavy chain (MHC) were used as an index of phenotypic change in developing and adult EOMs after these visual insults. In rats that were dark reared during the visual critical period, the proportion of EOM fibers expressing either fast or slow MHCs was decreased significantly. EOM-specific myosin was also sensitive to dark rearing during the critical period, as evidenced by a significant decrease in its mRNA in EOMs from these rats. EOM-specific MHC did not change in either dark-reared rats returned to normally illuminated conditions or in adult rats denied visual experience for a similar time period. These data suggest that there may be a critical period during development when alterations in visual activity have significant consequences for the eye muscle phenotype. In contrast to dark rearing, monocular deprivation had a minimal effect on expression of the typical myosin isoforms and no effect on EOM-specific myosin expression. Collectively, these data confirm the hypothesis that visual input to the oculomotor system during development modulates EOM-specific MHC expression.

Animals↗

PubMed1988

Binocularly deprived cats: binocular tests of cortical cells show regular patterns of interaction.

If an animal is prevented from receiving visual experience during an early developmental phase, pronounced dysfunctions are observed. Physiological tests reveal gross abnormalities in the striate cortex. Cells in visual cortex are either unresponsive of their response characteristics are erratic. Although fewer than normal numbers of binocular cells are found in cats reared with binocular lid suture, a population remains that can be activated by stimulation through either eye. We have studied cortical cells in binocularly deprived cats in order to specify monocular and binocular response characteristics. The primary hypothesis we have examined is that the abnormal response properties of these cells are a result of an irregular structure or substructure of the receptive fields. Kittens were binocularly lid-sutured soon after birth, and were studied physiologically at ages between 7 and 11 months. Standard techniques were used to record from single cells in striate cortex. Drifting gratings were presented to either eye or to both eyes together. In the latter case, the relative interocular phase was varied between the gratings so that the retinal disparity of the stimuli was changed. We confirmed the expected finding that most cells were either unresponsive or erratic in their response. Of the cells that responded, monocular tuning functions for orientation and spatial frequency of the stimulus were often irregular. However, even in these cases, binocular interaction patterns of cortical responses were nearly always highly regular and displayed phase-specific profiles. A model is presented that explains this finding and suggests how binocular deprivation may result in disorganized receptive-field structure.

Animals↗

PubMed1998

Visual activation patterns in patients with optic neuritis: an fMRI pilot study.

We studied the use of functional MRI (fMRI) with visual stimulation in nine patients with unilateral optic neuritis. Eight healthy subjects served as controls. Patients showed reduced activation upon stimulation of the affected eye, on average 33% (range 0 to 156%) of the average monocular activation in the control group. Decreased activation was also seen for the unaffected eye (61% of control values, range 3 to 133%). We conclude that fMRI with visual stimulation is feasible in patients with optic neuritis and deserves future study.

Adult↗

PubMed1993

Postnatal ontogeny of GABAA and benzodiazepine receptors in individual layers of rat visual cortex and the effect of visual deprivation.

The postnatal development of GABAA and benzodiazepine receptors was studied in the rat visual cortex with [3H]muscimol and [3H]flunitrazepam, respectively. The studies were performed by quantitative receptor autoradiography in the different cortical layers from normally raised rats and from monocularly deprived animals. In all cortical layers of normal rats there was a sharp (approx 3-fold) increase in [3H]muscimol binding from days 1 to 10. Between postnatal days 10 and 20 there was a considerable decrease in GABAA receptors; thereafter this decline continued until adulthood but at a more moderate rate. In all cortical layers, [3H]flunitrazepam binding increased sharply, also from day 1 to 10; at this age the adult values were practically attained. Monocular deprivation, by unilateral eyelid suture at the age of 11 days onwards lead to an increase in [3H]muscimol binding in cortical layers IV-VI. This increase in GABAA receptors was detectable at the age of 25 days onwards. In contrast, monocular deprivation did not alter the density of benzodiazepine receptors in any of the cortical layers, and this lack of effects was regardless of the duration of visual deprivation. The present results suggest that the development of GABAA receptors in the deeper cortical layers, but not that of benzodiazepine receptors, is seemingly regulated by the visual experience at a critical period of brain maturation.

Animals↗

PubMedDate not supplied

Amaurosis fugax challenges: best met by multispecialty approach to management.

1. Amaurosis fugax (AF) refers to transient, reversible loss of vision, typically monocular and of short duration. 2. Patients with AF present a diagnostic and therapeutic challenge, frequently requiring a multispecialty approach to management. It is important to determine whether or not there is an ocular cause of the problem. 3. In the absence of eye findings to explain the symptoms, the internist must direct the workup toward cardiogenic hypotension, migraine, carotid or vertebral-basilar artherosclerotic disease, cardiac embolic disorder, and other potential causes.

Blindness↗

PubMed2000

Binocular vision in older people with adventitious visual impairment: sometimes one eye is better than two.

PURPOSE: To determine the effect of adventitious visual impairment (low vision) on monocular and binocular spatial contrast sensitivity of older people. DESIGN: A between-within repeated measures design. PARTICIPANTS: Fifty-nine older adults between the ages of 50 and 96; 49 of the observers had age-related macular degeneration (AMD). MEASURES: Visual acuity screening and spatial contrast sensitivity. RESULTS: In almost half of the population with AMD, the sensitivity to spatial information, as measured by spatial contrast sensitivity, is worse when both eyes are used than when the stimuli are viewed with only one eye. This "binocular inhibition" is not related to the contrast sensitivity of the better eye or to acuities. Furthermore, this inhibition process is reflected primarily in images with medium to low spatial frequency components (medium to large size bars). CONCLUSIONS: These results have important implications for understanding the functional impact of low vision in older people. They suggest that almost one-half of older people with AMD view the world best using only one of their eyes, whereas for the other half, there is an advantage to using binocular vision for certain visual tasks.

Aged↗

PubMed1989

Postnatal development of neuropeptide Y-like immunoreactivity in area 17 of normal and visually deprived rhesus monkeys.

Immunocytochemical methods were used to examine neuropeptide Y (NPY) immunoreactive neurons and fibers in area 17 of rhesus monkeys during the first year of life. NPY-immunoreactive (+) neurons are nonpyramidal cells which are either multipolar, bipolar, or bitufted in shape. They occur most frequently in layer 6 and the subjacent white matter, are sparser in the supragranular layers, and absent from layer 4C. Labeled somata in the supragranular layers are smaller compared to those in layer 6 and the white matter. A typical axon originates from the NPY+ soma or from a primary dendrite and frequently is varicose. Distribution and morphologies of NPY+ neurons in area 17 of infants are similar to those of adult monkeys. Thus, it seems that NPY+ neurons in rhesus monkeys are mature from birth. NPY+ fibers occur in area 17 from birth; however, they differ in density and distribution from those of older infant and adult monkeys. At birth, a prominent fiber plexus is found in the deepest part of layer 1, and another in the white matter. Immunoreactive processes are sparse in the remaining cortical gray, except for some vertical fibers extending from pia to white matter. By 4 months of age, labeled fibers form a coarse network in layers 2, 3, 5, and 6. In addition, a distinct plexus extends through layers 4B, 4A, and the lowest aspect of layer 3. Also, a thin immunoreactive fiber band is found at the bottom of layer 4C. In the remainder of layer 4C, NPY+ fibers are scant. The supragranular layers also exhibit a unique immunoreactive "snarl" of fibers. Increases in density of NPY+ processes in the older infants are gradual so that between 7 and 13 months of age, NPY+ fibers appear to have achieved adultlike densities. These observations indicate that NPY+ fibers in area 17 of newborn rhesus monkeys undergo postnatal maturation which reaches a plateau around 4 months of age. After monocular visual deprivation from birth to 4 months of age, either by eyelid suture or by occlusion with an opaque contact lens, density and distribution of NPY+ neurons and fibers, including snarls, appear similar to those of age-matched undeprived infants. Thus, disruption of the normal binocular input does not seem to arrest the maturation of the NPY system in area 17 of rhesus monkeys during a sensitive period of early postnatal development.

Animals↗

PubMed1993

Plasticity of an aberrant geniculocortical pathway in neonatally lesioned cats.

Geniculocortical afferents to the lateral suprasylvian (LS) visual area come only from the C layers in normal adult cats. After neonatal lesions of areas 17 and 18, inputs to the LS area also arise from the A layers. We studied the plasticity of this aberrant pathway. We made lesions in areas 17 and 18 of newborn kittens, some of which were then monocularly deprived. In lesioned undeprived cats, retrograde tracing confirmed projections to the LS area from both the A and A1 as well as the C geniculate layers. In lesioned deprived cats, geniculate afferents from the A layers to the LS area came mainly from the layer receiving a normal visual input. We conclude that the development of the abnormal pathway from the A layers to the LS area is influenced by patterned visual activity.

Animals↗

PubMed1993

Visual input and lateralization of brain function in learning in the chick.

Several lines of evidence (biochemical, neuroanatomical, electrophysiological, and behavioural) have indicated a critical role for the intermediate medial hyperstriatum ventrale of the chick forebrain in the acquisition of a passive avoidance response. Previous lesion studies indicated that bilateral or left, but not right, pretraining intermediate medial hyperstriatum ventrale lesions interfere with the acquisition of this task. We have further analysed this asymmetrical involvement of the intermediate medial hyperstriatum ventrale by use of a monocular learning protocol and intermediate medial hyperstriatum ventrale lesions (sham, bilateral, or unilateral). The results indicated that there is interocular transfer of information of passive avoidance learning between the two eye systems, with a tendency to be more successful from the right eye system to the left than in the opposite direction. As in binocular conditions, bilateral pretraining intermediate medial hyperstriatum ventrale lesions impair learning in monocularly trained animals. Unilateral lesions to either left or right monocularly trained experimental animals resulted in amnesia when they were made to the right intermediate medial hyperstriatum ventrale and the chicks were trained/tested with the left eye open. These results indicate that, although right intermediate medial hyperstriatum ventrale lesions do not result in amnesia in binocular animals, this region is capable of participating in memory acquisition processes. They also suggest a connection between lateralization of intermediate medial hyperstriatum ventrale function in passive avoidance learning and the behavioural and structural visual asymmetries known to occur in chicks.

Animals↗

PubMed2002

Foveal and eccentric acuity in one-eyed observers.

The purpose of these two experiments was to examine the effects of enucleation on the foveal and near-periphery acuity of human observers. In Experiment 1, using high contrast illiterate-E optotypes, we measured foveal and 7-degree eccentric (nasal and temporal) acuity in the remaining eye of unilaterally enucleated children and adults. The data were compared to those of the fellow or 'good eye' of age-matched non-amblyopic and amblyopic strabismic observers-a different kind of monocular deprivation-and binocularly normal subjects. The main finding was that the 7-degree eccentric acuity of enucleated observers and normal controls was best, followed by that of the non-amblyopic and lastly, the amblyopic subjects. There were no naso-temporal asymmetries. In Experiment 2, foveal and 7-degree eccentric acuities of enucleated and binocularly normal subjects were tested at 96, 13.5 and 4.7% contrast levels using the same kind of stimuli. The foveal acuity of the enucleated observers was better than the monocular acuity of controls at all contrasts, and equivalent to their binocular acuity. The eccentric acuity of the enucleated observers was better at the two low contrast levels. No naso-temporal asymmetries were found in either group at any contrast level. These findings suggest that, in humans, visual deprivation from unilateral enucleation does not result in a naso-temporal asymmetry in the near periphery.

Adolescent↗

PubMed2005

Prior experience enhances plasticity in adult visual cortex.

The brain has a remarkable capacity to adapt to alterations in its sensory environment, which is normally much more pronounced in juvenile animals. Here we show that in adult mice, the ability to adapt to changes can be improved profoundly if the mouse has already experienced a similar change in its sensory environment earlier in life. Using the standard model for sensory plasticity in mouse visual cortex-ocular dominance (OD) plasticity-we found that a transient shift in OD, induced by monocular deprivation (MD) earlier in life, renders the adult visual cortex highly susceptible to subsequent MD many weeks later. Irrespective of whether the first MD was experienced during the critical period (around postnatal day 28) or in adulthood, OD shifts induced by a second MD were faster, more persistent and specific to repeated deprivation of the same eye. The capacity for plasticity in the mammalian cortex can therefore be conditioned by past experience.

Aging↗

PubMed1993

Effects of nerve growth factor on neuronal plasticity of the kitten visual cortex.

1. The effect of intraventricular administration of nerve growth factor (NGF) by means of a cannula-minipump system was studied in kittens monocularly deprived during the critical period. The ocular dominance of area 17 neurones of NGF-treated and control kittens was determined by conventional extracellular recordings. The soma size of cells in A and A1 laminae of the lateral geniculate nucleus (LGN) was also evaluated in Cresyl Violet preparations. 2. Binocularly responsive neurons were found to be significantly more numerous in NGF-treated than in control kittens. The shrinkage of cells from the deprived LGN laminae normally observed in control kittens was prevented by NGF administration. 3. Following an initial period of monocular deprivation (MD) kittens subsequently treated with NGF showed a substantial recovery of functional binocular connections. 4. These findings indicate that the administration of NGF during the period of deprivation reduces the amblyopic effects of MD, while its administration to kittens with both eyes open following the initial deprivation promotes recovery of the deprived eye. 5. Neurotrophic factors may contribute to the regulation of experience-dependent modifications of synaptic connectivity in the visual cortex.

Amblyopia↗

PubMed1994

GABAA receptor subunit immunoreactivity in primate visual cortex: distribution in macaques and humans and regulation by visual input in adulthood.

Subunit proteins that make up functional GABAA receptors were localized immunocytochemistry in the primary visual cortex (area 17) of adult monkeys and humans. Immunoreactivity for the alpha 1, beta 2/3, and gamma 2 subunits is greatest in layers (II-III, IVA and IVC) of monkey area 17 that contain the highest density of GABA neurons and terminals. Immunostaining for each subunit is unevenly distributed in layers II and III, where patches of immunoreactivity correspond to regions of intense cytochrome oxidase (CO) staining, and in layer IVA, where intense immunoreactivity forms a honeycomb pattern identical to the CO staining pattern. Immunoreactivity for the subunits is localized principally within the neuropil, which, by simultaneous comparison with the distribution of microtubule-associated protein immunostaining, was found to include bundles of thin dendrites and zones of numerous dendritic segments. In addition, gamma 2 immunostaining surrounds the somata of a subpopulation of GABAergic neurons, immunoreactive for the calcium-binding protein parvalbumin. All three subunits are present in the somata and processes of neurons that occupy the white matter subjacent to monkey area 17. In human visual cortex, the alpha 1, beta 2/3, and gamma 2 subunits are distributed in a manner similar to that found in monkeys, with relatively intense immunostaining in layers IVC and IVA. In layer IVC, vertical stripes of intense receptor immunostaining (20-30 microns wide) alternate with wider stripes of pale immunostaining (30-60 microns wide). In the upper and lower halves of IVC beta, these stripes form lattices similar to those in layers IVC and IVA of monkeys. Following monocular deprivation by intravitreal injections of TTX in adult monkeys, immunoreactivity for each subunit in layer IVC consists of alternating intensely and lightly stained stripes. Comparison with the pattern of CO staining indicates that intense immunostaining for alpha 1, beta 2/3, and gamma 2 occurs in normal-eye stripes while abnormally light immunostaining is present in deprived-eye stripes. For all three subunits, immunoreactivity in deprived-eye stripes is reduced within 5 d of monocular deprivation and remains abnormally low for deprivations that extend to at least 30 d. These findings indicate that each of several GABAA receptor subunits adopt similar laminar and compartmental distributions in monkey and human area 17 and are likely to be expressed by the same neurons. The deprivation-dependent reduction in immunoreactivity for alpha 1, beta 2/3, and gamma 2 subunits suggests that all are regulated by visually driven activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMedDate not supplied

Experience-dependent changes in NMDAR1 expression in the visual cortex of an animal model for amblyopia.

When normal binocular visual experience is disrupted during postnatal development, it affects the maturation of cortical circuits and often results in the development of poor visual acuity known as amblyopia. Two main factors contribute to the development of amblyopia: visual deprivation and reduced binocular competition. We investigated the affect of these two amblyogenic factors on the expression of the NMDAR1 subunit in the visual cortex because activation of the NMDA receptor is a key mechanism of developmental neural plasticity. We found that disruption of binocular correlations by monocular deprivation promoted a topographic loss of NMDAR1 expression within the cortical representations of the central visual field and the vertical and horizontal meridians. In contrast, binocular deprivation, which primarily affects visual deprivation, promoted an increase in NMDAR1 expression throughout the visual cortex. These different changes in NMDAR1 expression can be described as topographic and homeostatic plasticity of NMDA expression, respectively. In addition, the changes in NMDA expression in the visual cortex provide a greater understanding of the neural mechanisms that underlie the development of amblyopia and the potential for visual recovery.

Amblyopia↗

PubMed1997

Nasotemporal asymmetries in V1: ocular dominance columns of infant, adult, and strabismic macaque monkeys.

To quantify asymmetries of input from the two eyes into each cerebral hemisphere, we measured ocular dominance column (ODC) widths and areas in the striate visual cortex (area V1) of macaque monkeys. Ocular dominance stripes in layer 4C were labeled by using transneuronal transport of intraocularly injected wheat germ agglutinin-horseradish peroxidase (WGA-HRP) or cytochrome oxidase (CO) histochemistry, after deafferentation of one eye or even by leaving afferent input intact. In infant monkey aged 4 and 8 weeks, ocular dominance stripes labeled by WGA-HRP appeared adultlike with smooth, sharply defined borders. In normal infant and normal adult macaque, ocular dominance stripes driven by the nasal retina (i.e., contralateral eye) were consistently wider than stripes driven by the temporal retina (i.e., ipsilateral eye). Asymmetries in the percentage of area V1 driven by nasal vs. temporal ODCs showed a similar "nasal bias": in infant macaque, approximately 58% of ODCs in V1 were driven by nasal retina, and in adult macaque approximately 57%. The asymmetries tended to be slightly smaller in opercular V1 and greater in calcarine V1. "Spontaneous" ocular dominance stripes were revealed by CO staining of V1 in a naturally strabismic monkey and in a monkey made strabismic by early postnatal alternating monocular occlusion. In these animals, ocular dominance stripes and CO blobs corresponding to the nasal retina stained more intensely for CO in both the right and left V1. ODC spacing and the nasotemporal asymmetry in ODC width and area were similar in strabismic and normal monkeys. Our results in normal monkeys extend the observations of previous investigators and verify that nasotemporal inputs to opercular and calcarine V1 are unequal, with a consistent bias favoring inputs from the nasal retina. The CO results in strabismic macaque suggest that the nasal ODC bias promotes interocular suppression when activity in neighboring ODCs is decorrelated by abnormal binocular experience in infancy.

Aging↗