Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Primary 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.

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

At least 415 records · Page 23Linked to original sources
PubMed1990

Color and contrast sensitivity in the lateral geniculate body and primary visual cortex of the macaque monkey.

We tested color and contrast sensitivity in the magnocellular and parvocellular subdivisions of the lateral geniculate body and in layers 2, 3, 4B, and 4C alpha of visual area 1 to obtain physiological data on the degree of segregation of the 2 pathways and on the fate of the color and contrast information as it is transmitted from the geniculate to the cortex. On average, magnocellular geniculate cells were much less responsive than parvocellular cells to shifts between 2 equiluminant colors. Nevertheless, many magnocellular cells (though not all) continued to give some response at equiluminance. As expected from previous studies, luminance contrast sensitivity differed markedly between magnocellular and parvocellular layers. In V-1, the properties of cells in the magnorecipient layers 4C alpha and 4B faithfully reflected the properties of magnocellular geniculate cells, showing no evidence of any parvocellular input. Like magnocellular geniculate cells, they showed high contrast sensitivity, and with color contrast stimuli they showed large response decrements at equiluminance. In the interblob regions of cortical layers 2 and 3, which anatomically appear to receive most of their inputs from parvorecipient layer 4C beta, contrast sensitivities of some of the cells were compatible with a predominantly parvocellular input. Other interblob cells had sensitivities intermediate between magno- and parvocellular geniculate cells, suggesting a possible contribution from the magnocellular system. Many cells in cortical layers 2 and 3 responded to color-contrast borders equally well at all relative brightnesses of the 2 colors, including equiluminance. We recorded from many direction- and disparity-selective cells in V-1: most of the direction-selective and all of the clearly stereo-selective cells were located in layer 4B.

Animals↗
PubMed1986

Orientation selectivity of synaptic potentials in neurons of cat primary visual cortex.

Neurons of the visual cortex of the cat were penetrated with intracellular electrodes and postsynaptic potentials evoked by visual stimuli recorded. By alternately polarizing the cell with steady current injected through the recording electrode, IPSPs and EPSPs could be recorded and analyzed independently. Hyperpolarizing current suppressed IPSPs and enhanced EPSPs by moving the membrane potential toward the IPSP equilibrium potential. Depolarizing the cell toward the EPSP equilibrium potential enhanced IPSP. The responses to electrical stimulation of the LGN, where EPSPs and IPSPs could be distinguished easily by virtue of their characteristic latencies and shapes, were used to set the current injection to the appropriate level to view the two types of synaptic potential. EPSPs were found to be well oriented in that maximal depolarizing responses could be evoked at only one stimulus orientation; rotating the stimulus orientation in either direction produced a fall in the EPSP response. IPSPs were also well tuned to orientation, and invariably the preferred orientations of EPSPs and IPSPs in any one cell were identical. In addition, no systematic difference in the width of tuning of the two types of potential was seen. This result has been obtained from penetrations of over 30 cortical cells, including those with simple and complex receptive fields. It is concluded that orientation of cortical receptive fields is neither created nor sharpened by inhibition between neurons with different orientation preference. The function of inhibition evoked simultaneously with excitation by optimally oriented stimuli has yet to be determined, though it is likely to be the mechanism underlying other cortical receptive field properties, such as direction selectivity and end-stopping.

Animals↗
PubMed1984

Specificity of intrinsic connections in primate primary visual cortex.

Several recent studies have suggested a patchy system of intrinsic lateral connections in area 17 of the macaque monkey. To see whether this pattern bore any relationship to the cytochrome oxidase blobs we made multiple tiny injections of horseradish peroxidase into layers 2 and 3 of area 17, small enough so that some of the injections (or their cores) were entirely inside a single blob, or entirely outside. When the injection centers were entirely in blobs, the label in layers 2 and 3 was transported preferentially to nearby blobs, avoiding nonblob areas. When the injections were in nonblob areas, the label was found predominantly in surrounding nonblob areas, avoiding the blobs. Besides this lateral transport, label was also present in the layers below 2 and 3: the label in layers 4 and 6 was very restricted, occupying roughly the diameter of the injection core and presumably representing axons of cell bodies at the injection site; in layer 5 diffusely labeled patches observed the same blob/nonblob segregation seen above layer 4.

Animals↗
PubMed1984

[Demonstration of an effect of (3H)-L-proline on the number of dendritic spines on stellate cells of the primary visual cortex in Macaca during the critical period].

A morphometric study in cortical layer IVC of Macaca area 17 was performed during the critical period. A 20% increase in the number of dendritic spines was observed in neurons with horizontal dendritic tree in the cortical sublayer IVC alpha after an intraocular injection of (3H)-L-proline. A neuroactive role of this amino acid is discussed.

Animals↗
PubMed1995

Differential properties of cells in the feline primary visual cortex providing the corticofugal feedback to the lateral geniculate nucleus and visual claustrum.

We have examined the responses of 141 layer VI cells in the feline visual cortex. Within this group we compared the responses of a subpopulation of cells checked for connectivity by electrical stimulation in the dLGN and the visual claustrum. The antidromically identified corticogeniculate projecting cells had relatively short receptive fields, as judged from length response curves, measured quantitatively, and were located at the "short" end of the receptive field length spectrum seen in the general population. Of the 17 corticogeniculate projecting cells, 71% were S type cells, which were typically monocular and directionally selective, with relatively long latencies following electrical stimulation. The remaining 29% were C type cells, also directionally selective, but with a wider spread of ocular dominance preferences and shorter latencies following electrical stimulation. S and C type subpopulations did not differ in their receptive field lengths. The mean receptive field length for this subpopulation was 2.2 degrees +/- 0.27, the shortest field being 1 degrees and the longest 5 degrees. The five layer VI cells activated by electrical stimulation from electrodes within the dorsocaudal (visual) claustrum all had much longer receptive field lengths than the corticogeniculate population, often 10 degrees or longer and were monocular and directionally selective S type cells. These data indicate that the information carried in the corticogeniculate stream (and that from layer VI directly to layer IV carried by axon collaterals) is relatively tightly focused in spatial terms whilst the less spatially focused, long receptive field output from layer VI projects to the claustrum.

Animals↗
PubMed1995

Cytochrome-oxidase blobs in cat primary visual cortex.

Cytochrome-oxidase blobs are central to two of the most influential ideas in contemporary visual neuroscience--cortical modularity and parallel processing pathways. In particular, the regular 2D array of cytochrome-oxidase-rich blobs in primate visual cortex is arguably the most compelling evidence for cortical modularity and has been hypothesized to mark a separate processing stream through the visual cortex. Although previously a variety of mammals have been studied, blobs have only been demonstrated in the visual cortex of primates, which has led to the conclusion that blobs represent a primate-specific feature of visual cortical organization. Here we demonstrate the presence of cytochrome-oxidase blobs in a nonprimate species. Throughout the full tangential extent of layers II-III in cat visual cortex the cytochrome-oxidase staining pattern is distinctly patchy, with the darkly stained blobs forming a regular 2D array. In addition, the blobs in cat visual cortex are functionally related to the underlying ocular dominance columns. The presence of cytochrome-oxidase blobs in the cat clearly demonstrates that they no longer can be considered a primate-specific feature of visual cortical organization.

Animals↗
PubMed1996

Contextual modulation in primary visual cortex.

We studied extra-receptive field contextual modulation in area V1 of awake, behaving macaque monkeys. Contextual modulation was studied using texture displays in which texture covering the receptive field (RF) was the same in all trials, but the perceptual context of this texture could vary depending on the configuration of extra-RF texture elements. We found robust contextual modulation when disparity, color, luminance, and orientation cues variously defined a textured figure centered on the RF of V1 neurons. We found contextual modulation to have a spatial extent of approximately 8 to 10 degrees diameter parafoveally. Contextual modulation correlated with perceptual experience of both binocularly rivalrous texture displays and of displays with a simple example of surface occlusion. We found contextual modulation in V1 to have a characteristic latency of 80-100 msec after stimulus onset, potentially allowing feedback from extrastriate areas to underlie to this effect.

Animals↗
PubMed1998

Functional streams and local connections of layer 4C neurons in primary visual cortex of the macaque monkey.

The primate visual system is composed of multiple, functionally specialized cortical areas. The functional diversity among areas is thought to reflect different contributions from early parallel visual pathways to the area V1 neurons providing input to "higher" cortical areas. The M pathway is believed to provide information about motion and contrast, via layer 4B of V1, to dorsal visual areas. The P pathway is believed to provide information about shape and color, via layer 2/3 of V1, to ventral visual areas, with specialized contributions from cytochrome-oxidase (CO) blob versus interblob neurons. However, the detailed anatomical relationships between the M and P pathways and the neurons in V1 that provide input to higher extrastriate cortical areas are poorly understood. To study these relationships, spiny stellate neurons in the M- and P-recipient layers of V1, 4Calpha and 4Cbeta, respectively, were intracellularly labeled, and their axonal and dendritic arbors were reconstructed. We find that neurons with dendrites in upper layer 4Calpha project axons to layer 4B and CO blobs in layer 2/3, thus relaying M input to these regions. Other neurons in lower layer 4Calpha provide M input to interblobs. These cells have either (1) dendrites restricted to lower layer 4Calpha and axons specifically targeting layer 2/3 interblobs, or (2) dendrites in lower 4Calpha and 4Cbeta and axons targeting blobs and interblobs. P-recipient layer 4Cbeta neurons have dense axonal arbors in both blobs and interblobs but not layer 4B. Quantitative analyses reveal that 4Calpha cells provide approximately five times more synapses than 4Cbeta cells to layer 4B, whereas 4Cbeta cells provide five times more synapses than 4Calpha cells to layer 2/3. These observations imply that M input is dominant in layer 4B. In layer 2/3, both blobs and interblobs receive M and P input, but the P input is dominant, and M input to interblobs derives exclusively from a subpopulation of M afferents that targets lower 4Calpha, not from afferents targeting only upper 4Calpha (cf. Blasdel and Lund, 1983). We speculate that the M and P pathways to interblobs are "X-like" linear systems, whereas blobs also receive nonlinear "Y-like" M input.

Animals↗
PubMed1998

Synaptic and neurochemical characterization of parallel pathways to the cytochrome oxidase blobs of primate visual cortex.

The primary visual cortex (V1) of primates is unique in that it is both the recipient of visual signals, arriving via parallel pathways (magnocellular [M], parvocellular [P], and koniocellular [K]) from the thalamus, and the source of several output streams to higher order visual areas. Within this scheme, output compartments of V1, such as the cytochrome oxidase (CO) rich blobs in cortical layer III, synthesize new output pathways appropriate for the next steps in visual analysis. Our chief aim in this study was to examine and compare the synaptic arrangements and neurochemistry of elements involving direct lateral geniculate nucleus (LGN) input from the K pathway with those involving indirect LGN input from the M and P pathways arriving from cortical layer IV. Geniculocortical K axons were labeled via iontophoretic injections of wheat germ agglutinin-horseradish peroxidase into the LGN and intracortical layer IV axons (indirect P and M pathways to the CO-blobs) were labeled by iontophoretic injections of Phaseolus vulgaris leucoagglutinin into layer IV. The neurochemical content of both pre- and postsynaptic profiles was identified by postembedding immunocytochemistry for gamma-amino butyric acid (GABA) and glutamate. Sizes of pre- and postsynaptic elements were quantified by using an image analysis system, BioQuant IV. Our chief finding is that K LGN axons and layer IV axons (indirect input from M and P pathways) exhibit different synaptic relationships to CO blob cells. Specifically, our results show that within the CO blobs: 1) all K cell axons contain glutamate, and the vast majority of layer IV axons contain glutamate with only 5% containing GABA; 2) K axons terminate mainly on dendritic spines of glutamatergic cells, while layer IV axons terminate mainly on dendritic shafts of glutamatergic cells; 3) K axons have larger boutons and contact larger postsynaptic dendrites, which suggests that they synapse closer to the cell body within the CO blobs than do layer IV axons. Taken together, these results suggest that each input pathway to the CO blobs uses a different strategy to contribute to the processing of visual information within these compartments.

Animals↗
PubMed1996

Interareal synchronization in the visual cortex.

The primary visual cortex (V1) is part of a highly interconnected network of cortical areas, hierarchically organized but operating concurrently across hierarchical levels. The high degree of reciprocal interconnection among visual cortical areas provides a framework for their interaction during the performance of visual scene analysis. The functional interdependency of visual cortical areas which develops during scene analysis can be investigated by techniques which measure interareal correlated activity. Evidence from monkeys performing a visual pattern discrimination suggests that synchronization of aperiodic activity from neuronal ensembles in cortical areas at different hierarchical levels is a relevant aspect of visual function. The near-periodic nature of the synchronized response to moving light bars in earlier studies may have been a result of the type of stimulus used. Various models of visual cortex are discussed in which interareal synchronization plays a functional role.

Animals↗
PubMed2000

The distribution of NADPH diaphorase and nitric oxide synthetase (NOS) in relation to the functional compartments of areas V1 and V2 of primate visual cortex.

The primary visual cortex (V1) of primates receives visual signals from cells in the koniocellular (K), magnocellular (M) and parvocellular (P) layers of the lateral geniculate nucleus (LGN). The functional role of the K pathway is unknown, but one proposal is that it modulates visual activity locally via release of nitric oxide (NO). One goal of this study was to examine the distribution of nitric oxide synthetase (NOS), the enzyme that produces NO, using immunocytochemistry for brain NOS (bNOS) or histochemistry for nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase activity in the V1 target cells of the K pathway and within the LGN itself. A second goal was to examine bNOS and NADPH diaphorase activity within proposed functional compartments in the second visual area (V2). We examined the LGN, V1 and V2 in squirrel monkeys, owl monkeys and bushbabies. In V1 and V2, we found that dense neuropil staining for NADPH diaphorase mirrored the pattern of high metabolic activity shown with cytochrome oxidase (CO) staining but did not necessarily mirror the pattern of immunolabeling seen with antibodies against NOS. The smooth stellate cells stained for NADPH diaphorase or bNOS were sparse and did not colocalize with LGN recipient zones in V1 or with the CO compartments in V2. LGN cells projecting to V1, including K, M and P cells, were negative for bNOS and NADPH diaphorase. Therefore, high levels of NOS are not limited to the K pathway. Instead, dense NOS activity is present in interneurons and within the neuropil of V1 and V2 that exhibit high metabolic demand.

Animals↗
PubMed2001

Endogenous serotonin contributes to a developmental decrease in long-term potentiation in the rat visual cortex.

The primary visual cortex shows synaptic plasticity during a postnatal "critical period," and its plasticity declines with development. Indeed, we found a developmental decrease in the induction of long-term potentiation (LTP) in the rat visual cortex. In visual cortex slices obtained from 2- to 3-week-old rats, tetanic stimulation (100 Hz for 1 sec, twice at an interval of 30 sec) of the white matter reproducibly induced LTP of field potentials in layer II/III. However, in slices from 5-week-old rats, the same tetanic stimulation failed to induce LTP. We hypothesized that endogenous serotonin (5-HT) is responsible for the developmental decrease in visual cortex LTP, because the induction of visual cortex LTP was suppressed by the addition of exogenous 5-HT (10 microm) and because the amount of 5-HT in the visual cortex increased during development. To test this hypothesis, we investigated the effect of methysergide, a 5-HT receptor antagonist, on the induction of visual cortex LTP. When visual cortex slices from 5-week-old rats were perfused with 50 microm methysergide, tetanic stimulation of the white matter induced robust LTP in layer II/III. Furthermore, serotonergic neurons were lesioned by intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT). LTP was induced in visual cortex slices from 5,7-DHT-treated, 5-week-old rats. These results suggest that the induction of visual cortex LTP in 5-week-old rats is suppressed by endogenous 5-HT. 5-HT may be a factor that determines a critical period for synaptic plasticity in the rat visual cortex.

5,7-Dihydroxytryptamine↗
PubMed1989

Nuclear terminations of corticoreticular fiber systems in rats.

Corticoreticular fiber systems were examined in adult albino and hooded rats using anterograde transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) and anterograde degeneration. WGA-HRP injections were made stereotactically into the medial prefrontal cortex, the medial agranular cortex, the anterior cingulate cortex, the face motor cortex, the forelimb motor cortex, the trunk-hindlimb motor cortex, the face somatosensory cortex, the primary auditory cortex, the secondary visual cortex and the primary visual cortex. With exception of the cingulate cortex (which is relatively inaccessible to lesioning methods) and the primary visual cortex, electrocautery lesions were made into these same cortical areas. The precise locations of cortical injection/lesion sites were corroborated on the basis of cortical cytoarchitectonic criteria, patterns of retrograde and anterograde thalamic labeling, and patterns of anterograde labeling in non-reticular brainstem nuclei such as the red nucleus, trigeminal nuclei and dorsal column nuclei. The heaviest corticoreticular projections arise from the medial agranular cortex. The medial prefrontal cortex also gives rise to consistently strong corticoreticular projections. The anterior cingulate cortex sends robust corticoreticular projections to the upper brainstem but relatively weak projections to the lower brainstem. With respect to the primary motor cortex, the face area gives rise to the densest corticoreticular projections, rivaling those emanating from the medial agranular cortex. The trunk-hindlimb area gives rise to substantial corticoreticular projections, but those originating from the forelimb area are modest and directed chiefly to midbrain and medullary levels. The face area of the somatosensory cortex gives rise to rather weak corticoreticular projections, while those arising from the primary auditory cortex are fewer still. Descending projections from the secondary visual cortex are sparse, with labeled terminals occurring in a few pontine and medullary reticular nuclei. Only one brainstem reticular nucleus (nucleus cuneiformis) was found to receive projections from the primary visual cortex, and this input was extremely sparse. Corticoreticular projections to the upper brainstem terminate predominantly ipsilateral to the cortical injection site, whereas medullary corticoreticular projections distribute bilaterally. Corticoreticular fibers from the medial agranular, face motor and trunk-hindlimb motor cortex terminate heavily in somatomotor brainstem reticular nuclei such as the pontis oralis, the pontis caudalis and the gigantocellularis.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed2001

MR imaging of the human brain at 1.5 T: regional variations in transverse relaxation rates in the cerebral cortex.

BACKGROUND AND PURPOSE: Heterogeneity in cortical signal intensity on T2-weighted MR images has been recently documented. Using a whole-brain, multiecho MR imaging technique, we sought to determine the T2 relaxation times of nine predefined regions in the cerebral cortex and one region in the deep gray matter. METHODS: Ten adult volunteers (nine men and one woman; age range, 18-40 y; average age, 30.8 y) underwent whole-brain imaging with an oblique coronal multiecho 3D Carr-Purcell-Meiboom-Gill MR sequence at 1000/25, 50, 75, 100, 125, and 150 (TR/TE). T2 measurements were obtained, with variably sized regions of interest, from the primary auditory cortex, primary visual cortex, caudate nucleus, superior frontal gyrus, inferior temporal gyrus, middle temporal gyrus, superior temporal gyrus, insula cortex, cingulate gyrus, and hippocampus. Repeated-measures analysis of variance was used to assess the existence of differences in T2 measurements among the anatomic locations. RESULTS: On the basis of T2 measurements, the gray matter structures examined could be divided into four statistically different groups. In ascending order of T2 measurements, the first group consisted of the primary auditory cortex and primary visual cortex; the second group, the caudate nucleus, superior frontal gyrus, inferior temporal gyrus, middle temporal gyrus, and superior temporal gyrus; the third group, the insula cortex; and the fourth group, the cingulate gyrus and hippocampus. CONCLUSION: Significant variation in T2 values among the cortical gray matter of the human brain exists.

Adolescent↗