SEARCH · Search PubMed

Results for “Visual Cortex”

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.

SourceResearch connectionFrom yearThrough year

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

At least 1,657 records · Page 92Linked to original sources

PubMed2000

Comparison of the laminar distribution of input from areas 17 and 18 of the visual cortex to the lateral geniculate nucleus of the cat.

The feedback from area 18 of the cat visual cortex to the lateral geniculate nucleus has been investigated by labeling and reconstructing seventeen axons of known receptive field position and eye preference. The distribution of boutons from each axon was quantified with respect to the compartments of the geniculate complex, and the results were compared with an equivalent analysis of fourteen area 17 axons. Area 18 axons form large, sparse arborizations that extend up to 1.9 mm laterally (1170 +/- 85 microm; mean +/- SEM), with a core of relatively dense innervation spanning on average 600 +/- 70 microm (mean +/- SEM). Thus, they have the potential to influence the transmission of visual information from well beyond their own classical receptive fields. In this respect, they are surprisingly similar to the axons from area 17, despite the fact that the two cortical areas have very different retinotopy. However, there are important differences between the pathways. Area 18 axons project more heavily to the C layers and medial interlaminar nucleus. Whereas the input from both areas to the A layers is biased toward the layer appropriate to the eye preference of each axon, the area 18 input to magnocellular layer C is not. The distribution of area 18 boutons favors the bottom of their preferred A layer, and the area 17 boutons favor the top. These differences mirror those seen in the afferent pathways, suggesting that each cortical area preferentially targets the cells from which it receives input. Finally, their greater diameter suggests that area 18 axons provide the earliest feedback signal in the corticogeniculate loop.

Animals↗

PubMed2000

Light-induced down-regulation of the rat class 1 dynein-associated protein robl/LC7-like gene in visual cortex.

Dynein and kinesin are the main microtubule-dependent motors that mediate intracellular movement in eukaryotic organisms. We have cloned a full-length cDNA encoding rat dynein light chain protein, robl/LC7-like (class 1), from visual cortex. We found that rat robl/LC7-like gene is highly expressed in neocortex and displays the unusual feature of being rapidly down-regulated by sensory stimulation. This effect was seen at both mRNA and protein levels in visual cortex, being detectable in as little as 45 min after the onset of visual stimulation. Down-regulation by sensory stimulation was also found within ocular dominance columns of area V1 in monocularly deprived monkeys. Our results suggest a high turnover rate of the robl/LC7-like protein and the presence of a repressor mechanism in neurons that is tightly coupled to synaptic stimulation.

Amino Acid Sequence↗

PubMed1984

'Real-motion' cells in the primary visual cortex of macaque monkeys.

Extracellular recordings were carried out in the primary visual cortex of behaving macaque monkeys. Neurons were activated by moving a visual stimulus across their receptive fields during periods of steady fixation and by moving their receptive fields (by visual tracking) across a motionless visual stimulus, taking care that the velocities of stimulus and eye movements were the same. The total cell population (108 neurons) ws divided into 3 groups according to the cell sensitivity to visual stimulus orientation (non-oriented cell and oriented cells) and to the presence or absence of antagonistic areas in in the receptive fields (oriented cells with antagonistic areas). All the non-oriented cells (n = 14) showed almost the same response to visual stimulation both during steady fixation and during visual tracking. Out of a total number of 86 oriented cells, 77 turned out to be activated by the visual stimulation both during fixation and tracking. Eight oriented cells gave a very weak response or no response at all to visual stimulation during smooth pursuit eye movements and one neuron of the same group showed a greater response during visual tracking than during fixation. Six out of 8 oriented cells with antagonistic areas showed almost the same response to the two types of visual stimulation, while the remaining two neurons showed very weak responses during smooth pursuit eye movements. Our results show that a small percentage (about 10%) of striate neurons in macaque monkeys gave very different responses to the same physical stimulation at retinal level, according to the presence or absence of slow eye movements (smooth pursuit eye movements). The activity of these neurons seems to be related to the real movement of something in the visual world, in spite of the retinal image movement per se.

Animals↗

PubMed1984

Claustral afferents to the rat's visual cortex.

Horseradish peroxidase (HRP) was injected electrophoretically into the rat's primary visual cortex (V1), and three other retinotopically organized cortical areas, anterior medial visual area (AM), posterior medial visual area (PM) and anterior lateral area (AL). While the HRP injections into V1 labelled many neurons in the ipsilateral claustrum, the injections in any of the three other visual areas labelled very few claustral neurons.

Afferent Pathways↗

PubMed1997

[Influence of visual stimuli on eye-position related activities of neurons in primary visual cortex (V1) of awake monkeys].

Extracellular recordings were made in the primary visual cortex (V1) in two awake monkeys to test the influence of visual stimuli on the eye-position related activites of the neurons. While the monkeys gazed on a fixation point (FP) positioned sequentially at different locations on a TV screen, two types of visual stimuli were presented on the same screen: (1) A small light ring flashed repeatedly around the FP or (2) A prefered light bar shifted continuously across the cell's receptive field (RF). Both stimuli significantly enhanced the eye-position related activities and correspondingly increased the incidence of the eye-position dependent neurons. The results show that the integration of information on vision and on eye position may take place at quite the earliest stage of the visual cortices.

Animals↗

PubMed1994

Regulation of basal release of GABA by noradrenaline in the kitten visual cortex.

To determine the modulatory effect of noradrenaline (NA) on basal release of gamma-aminobutyric acid (GABA), we measured the extracellular GABA with a brain microdialysis technique in the kitten visual cortex. Local infusion of NA through a cannula, which was implanted 2 mm away from the dialysis probe, gave rise to a marked increase in GABA release. This NA-induced GABA release was suppressed by tetrodotoxin, a sodium channel blocker, which was perfused at the probe site. The effect of NA was antagonized by pretreatment with metoprolol, a beta 1-selective antagonist. These results suggest that the cortical noradrenergic system may be involved in the regulation of basal GABA release that is possibly due to the activity of inhibitory neurones in the kitten visual cortex.

Animals↗

PubMed2005

Cross-modal activation of visual cortex during depth perception using auditory substitution of vision.

Previous neuroimaging studies identified multimodal brain areas in the visual cortex that are specialized for processing specific information, such as visual-haptic object recognition. Here, we test whether visual brain areas are involved in depth perception when auditory substitution of vision is used. Nine sighted volunteers were trained blindfolded to use a prosthesis substituting vision with audition both to recognize two-dimensional figures and to estimate distance of an object in a real three-dimensional environment. Using positron emission tomography, regional cerebral blood flow was assessed while the prosthesis was used to explore virtual 3D images; subjects focused either on 2D features (target search) or on depth (target distance comparison). Activation foci were found in visual association areas during both the target search task, which recruited the occipito-parietal cortex, and the depth perception task, which recruited occipito-parietal and occipito-temporal areas. This indicates that some brain areas of the visual cortex are relatively multimodal and may be recruited for depth processing via a sense other than vision.

Acoustic Stimulation↗

PubMed2002

Perceptual segregation of overlapping shapes activates posterior extrastriate visual cortex in man.

Objects in natural scenes are rarely seen in isolation, but are usually overlapping or partially occluding other objects. To recognize individual objects, the visual system must be able to segregate overlapping objects from one another. Evidence from lesions in humans and monkeys suggest that perceptual segregation of occluded or overlapping objects involves extrastriate visual cortex. In monkeys, area V4 has been shown to play an important role in recognizing occluded or poorly salient shapes. In humans, a retinotopic homologue of ventral V4 (V4v) has been described, but it is not known whether this area is also functionally homologous to area V4 in monkeys. In this study, we tried to localize the visual cortical regions involved in perceptual segregation of overlapping shapes using positron emission tomography (PET). Regional cerebral blood flow (rCBF) was measured in seven subjects while they discriminated the relative areas of simultaneously presented rectangular shapes. In the control condition, the shapes were displayed without overlaps; in a second condition, the shapes overlapped each other partially. In a third condition, the shapes did not overlap but had been reduced in salience by adding random noise to the stimuli. Contrasting the overlapping shape condition with the control condition identified a single region in the left posterior lateral occipital cortex. The rCBF in this region also increased, though more weakly, during discrimination of shapes embedded in noise, relative to the control condition. The region activated by segregation of overlapping shapes was located in the posterior occipital cortex close to the anterior border of area V2, near the average location of human V4v as determined by retinotopic mapping studies. The activation of this region of extrastriate visual cortex by a task that involved segregation of overlapping shapes is consistent with monkey V4 and human V4v being functionally homologous. We conclude that discrimination of overlapping shapes involves in particular a region of extrastriate visual cortex located in the left lateral occipital cortex and that this region may correspond to human V4v.

Adult↗

PubMed1985

Transient patterns of acetylcholinesterase activity in visual cortex of the rat: normal development and the effects of neonatal monocular enucleation.

This paper describes the normal development and disappearance of acetylcholinesterase (AChE) activity in layer IV of rat visual cortex and the effects of neonatal monocular enucleation on this transient pattern of AChE activity. Subjects were laboratory-born male or female Long-Evans rats. Some animals underwent monocular enucleation within 6 h of birth. Animals were sacrificed at various ages and AChE activity was detected histochemically in tissue sections. AChE activity is first detectable histochemically in visual cortex area 17 as a fine fiber-like plexus in layer IV at about 7 postnatal days of age. The intensity of the staining increases during the second postnatal week and reaches peak intensity at days 12-14. The intensity of the AChE staining in layer IV of area 17 appears to decrease during the third postnatal week and the dense AChE band disappears by postnatal day 21. The distribution of AChE in layer IV of area 17 corresponds closely to the field of termination of geniculocortical projections and the fiber-like pattern of AChE activity resembles the appearance of an axonal terminal field. Neonatal monocular enucleation results in a marked decrement in the spatial extent of the AChE activity in layer IV of cortical area 17. The AChE-positive plexus is lost in the medial regions of area 17 contralateral to the enucleated eye. AChE activity remains in the lateral part of area 17, probably corresponding to that part of area 17 innervated by secondary projections from the intact ipsilateral eye. The functional role of this transient AChE activity is unknown. The present data suggest that AChE activity is characteristic of geniculocortical axon terminals during the period of time in which they are establishing functional connections with postsynaptic sites in cortex.

Acetylcholinesterase↗

PubMed1998

Simultaneous determination of total and extracellular concentrations of the amino acid neurotransmitters in cat visual cortex by microbore liquid chromatography and electrochemical detection.

To investigate the influence of a partial sensory deprivation on the total and extracellular concentration of the amino acid neurotransmitters in cat visual cortex, two microbore HPLC methods were developed for the simultaneous determination of aspartate, glutamate, glycine, taurine and gamma-aminobutyric acid in cat brain extracts or microdialysis samples. For the determination of the total neurotransmitter concentrations in the visual cortex, the brains were quickly frozen and 200-microns cryostat sections were made. From these sections tissue samples of 2 x 2 mm2 containing the six cortical layers were dissected out of the central and peripheral parts of area 17. After homogenisation and centrifugation, the supernatants were used for quantitative amino acid analysis using an o-phthalaldehyde-tert.-butylthiol pre-column derivatisation HPLC gradient elution method on a microbore column (100 x 1 mm I.D.; C8) and single electrochemical detection. Microdialysis samples from area 17 were obtained every 15 min using 2-mm probes perfused with synthetic cerebrospinal fluid at a flow-rate of 1 microliter/min. After o-phthalaldehyde-tert.-butylthiol derivatisation they were analysed on a microbore column by isocratic elution and dual electrochemical detection. The instrumentation and the different separation parameters were optimised and standard curve, recovery, analytical precision and detection limits for each neurotransmitter were determined.

Animals↗

PubMedDate not supplied

[Morphofunctional types of rabbit visual cortex neurons during postnatal ontogeny].

Eight types of unit responses to flashes were singled out in the visual cortex of non-immobilized rabbits, with morphological identification of representatives of each type. Inhibition was predominant in pyramids responses. Two types of non-pyramid neurones were revealed: with an early excitation (reception of afferent impulses) and with a delayed activation (recurrent inhibition). The distribution of responses along the cortical depth confirms the concept of vertical organization in the functional specialization of neurones. In postnatal ontogenesis there occurs the maturation of stellate cells and the substitution of the immature mechanisms of responses (on pyramid neurones) with normal ones (involving all neuronal types).

Age Factors↗

PubMed1989

Blockade of NMDA-receptors prevents ocularity changes in kitten visual cortex after reversed monocular deprivation.

We investigated in the striate cortex of kittens whether the recovery from the effects of monocular deprivation that occurs after reverse occlusion requires activation of N-methyl-D-aspartate (NMDA) receptors. The right eye of 3-4-week-old kittens was closed by lid suture for one week. Subsequently this eye was reopened and the left eyelid sutured closed for another week. During this second week, the NMDA-receptor antagonist, 2-amino-5-phosphonovaleric acid (APV), was infused from an osmotic minipump into the left visual cortex (50 nmol/h), while the right visual cortex was infused only with vehicle solution (saline) as control. At the end of the second week, the ocular dominance of striate cortical neurons was assessed with single unit recording. In the control hemispheres, the large majority of neurons was dominated by the newly opened eye, while in the APV-treated hemispheres most neurons were still dominated by the newly deprived eye. In addition, neurons in the APV-treated hemispheres were less responsive and showed a reduction of orientation tuning. These data confirm that chronic blockade of cortical NMDA-receptors disrupts the disconnection of deprived pathways after monocular deprivation and reduces both responsiveness and orientation selectivity of cortical neurons. In addition they indicate that blockade of NMDA-receptors prevents also vision-dependent recovery of deprived pathways after reverse occlusion.

2-Amino-5-phosphonovalerate↗

PubMed1988

The development of orientation and direction selectivity in the rabbit visual cortex.

The postnatal development of orientation and direction selectivity of single cells was examined in the primary visual cortex of rabbits. The percentage of cells which were orientation-selective reached adult levels by day 30, whereas the proportion of cells which were direction-selective did not reach adult levels until day 60. Differences in the time course of development of orientation and direction selectivity, together with data previously reported on differences in the effects of deprivation on orientation and direction selectivity, suggest that (1) different mechanisms underly the organization of orientation and direction selectivity and (2) the critical periods for the effects of deprivation on orientation and direction selectivity reflect the different time course of the normal development of these two response properties.

Aging↗

PubMed1999

Dendritic asymmetry cannot account for directional responses of neurons in visual cortex.

A simple model was proposed to account for the direction selectivity of neurons in the primary visual cortex, area V1. In this model, the temporal asymmetries in the summation of inhibition and excitation that produce directionality were generated by structural asymmetries in the tangential organization of the basal dendritic tree of cortical neurons. We reconstructed dendritic trees of neurons with known direction preferences and found no correlation between the small biases of a neuron's dendritic morphology and its direction preference. Detailed simulations indicated that even when the electrotonic asymmetries in the dendrites were extreme, as in cortical Meynert cells, the biophysical properties of single neurons could contribute only partially to the directionality of cortical neurons.

Animals↗

PubMed2004

Population coding of orientation in the visual cortex of alert cats--an information theoretic analysis.

We studied the encoding of stimulus orientation in the visual cortex of alert animals using information theory methods. Based on a labeled-line code, the encoding of orientation was mostly synergistic and only few pairs coded redundant. The synergy contributed about 20% of the information and was strongest for sites with distinct tuning curves. A recently proposed decomposition of synergy revealed that redundancy introduced by common tuning preferences is more than just compensated by noise correlations which mostly contributed synergistically. Based on a pooled response code, the contribution of noise correlations diminished resulting in a severe information loss. Thus, to operate economically, cortical neurons should either employ a labeled-line code or, if using pooled responses, be highly selective in choosing afferents.

Animals↗

PubMed1982

Central core control of developmental plasticity in the kitten visual cortex: II. Electrical activation of mesencephalic and diencephalic projections.

Fifteen dark-reared, 4- to 5-week-old kittens were stimulated monocularly with patterned light while they were anesthetized and paralyzed. Six of these kittens were exposed to the light stimuli only, in four kittens the light stimuli were paired with electric stimulation of the mesencephalic reticular formation and in five kittens with electric activation of the medial thalamic nuclei. Throughout the conditioning period, the ocular dominance of neurons in the visual cortex was determined from evoked potentials that were elicited either with electric stimulation of the optic nerves or with phase reversing gratings of variable spatial frequencies. In two kittens, ocular dominance changes were assessed after the end of the conditioning period by analyzing single unit receptive fields. Monocular stimulation with patterned light induced a marked shift of ocular dominance toward the stimulated eye, when the light stimulus was paired with electric activation of either the mesencephalic reticular formation or of the medial thalamus. Moreover, a substantial fraction of cells acquired mature receptive fields. No such changes occurred with light or electric stimulation alone. It is concluded that central core projections which modulate cortical excitability gate experience-dependent modifications of connections in the kitten visual cortex.

Animals↗

PubMedDate not supplied

Two methods of catecholamine depletion in kitten visual cortex yield different effects on plasticity.

As first clearly demonstrated by the experiments of Wiesel and Hubel, the developing visual cortex is exquisitely sensitive to sensory deprivation. Temporary closure of one eye of a kitten during a critical period that extends from 3 weeks to 3 months of age results in a dramatic cortical reorganization such that most neurones, originally binocularly driven, are dominated exclusively by the open eye. Recently, attention has been directed to chemical factors which may influence the degree of plasticity during the critical period. The work of Kasamatsu and pettigrew suggests that cortical catecholamines, especially noradrenaline (NA), are essential for the normal plastic response to visual deprivation. In an effort to clarify the role of NA in visual cortical plasticity, we have monocularly deprived kittens whose cortex had been depleted of catecholamines by the neurotoxin 6-hydroxydopamine (6-OHDA). We used two strategies to deplete cortical NA: the first, pioneered by Kasamatsu el al., utilized osmotic minipumps to deliver 6-OHDA to visual cortex; the second involved systemic neonatal injections of 6-OHDA, a technique which has proved effective in rodents. We found, using high-pressure liquid chromatography (HPLC), that both techniques produced a substantial reduction in the level of cortical NA. However, single unit recording in area 17 revealed that the plastic response to monocular deprivation (MD) was only diminished in the kittens depleted by minipump.

Animals↗

PubMed1999

Topographic shear and the relation of ocular dominance columns to orientation columns in primate and cat visual cortex.

Shear has been known to exist for many years in the topographic structure of the primary visual cortex, but has received little attention in the modeling literature. Although the topographic map of V1 is largely conformal (i.e. zero shear), several groups have observed topographic shear in the region of the V1/V2 border. Furthermore, shear has also been revealed by anisotropy of cortical magnification factor within a single ocular dominance column. In the present paper, we make a functional hypothesis: the major axis of the topographic shear tensor provides cortical neurons with a preferred direction of orientation tuning. We demonstrate that isotropic neuronal summation of a sheared topographic map, in the presence of additional random shear, can provide the major features of cortical functional architecture with the ocular dominance column system acting as the principal source of the shear tensor. The major principal axis of the shear tensor determines the direction and its eigenvalues the relative strength of cortical orientation preference. This hypothesis is then shown to be qualitatively consistent with a variety of experimental results on cat and monkey orientation column properties obtained from optical recording and from other anatomical and physiological techniques. In addition, we show that a recent result of Das and Gilbert (Das, A., & Gilbert, C. D., 1997. Distortions of visuotopic map match orientation singularities in primary visual cortex. Nature, 387, 594-598) is consistent with an infinite set of parameterized solutions for the cortical map. We exploit this freedom to choose a particular instance of the Das-Gilbert solution set which is consistent with the full range of local spatial structure in V1. These results suggest that further relationships between ocular dominance columns, orientation columns, and local topography may be revealed by experimental testing.

Journal Article↗