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At least 379 records · Page 21Linked to original sources

PubMed1991

Temporal interactions in the cat visual system. I. Orientation-selective suppression in the visual cortex.

The perception of a visual contour depends on the spatial and temporal context in which it is viewed. Interactions between visual contours are believed to underlie a wide range of perceptual phenomena, including geometric illusions and aftereffects, contrast adaptation, and visual masking. The physiological mechanisms that might underlie such interactions were studied in the visual cortex of the cat by recording responses of single neurons to pairs of brief stationary stimuli that were separated in time. The results revealed a long-lasting, orientation-selective suppression, termed "paired-pulse suppression," which was strongest at the cell's preferred orientation, but which was more broadly tuned for orientation than the excitatory response of the cell. Although the strength and duration of the suppression varied widely, some degree of response reduction was present in most cells studied. The function of this suppression may be to regulate the gain with which visual inputs are transmitted to cortical neurons, thus preventing response saturation and positive feedback.

Anesthesia↗

PubMed1988

Noradrenergic sprouting and beta-adrenergic receptor binding in the lateral geniculate nucleus of rats after unilateral visual cortex ablation.

One and two weeks after unilateral visual cortex (VC) ablation beta-adrenergic receptor binding is increased in the lateral geniculate nucleus (LGN) of both sides. 6 month later beta-receptor binding in the LGN is decreased again and no differences to untreated control animals are detectable. Using the glyoxylic acid fluorescence method for the visualization of amines a transient increase in the density of noradrenergic fibers in the dorsal part of the ipsilateral LGN can be demonstrated with a maximum 2 weeks after VC ablation. With longer survival time noradrenergic fibre density in the ipsilateral dorsal LGN (LGNd) decreases again and one year after the operation only few fluorescent fibres can be observed in the lateral part of the LGN compared to untreated control animals. Histologically an increased gliosis in the ipsilateral LGNd develops following removal of the visual cortex. In addition, degenerative changes in nerve fibers and terminals as well as neuronal degenerative changes are present and are most pronounced in the medial part of the ipsilateral dorsal LGN. Electron microscopically degenerating terminals in the dorsal part of the ipsilateral LGN can be identified as cortical afferents. Using potassium permanganate fixation typical noradrenergic axons with small dense core vesicles can be demonstrated in the LGN. In the denervated LGNd (i.e. the ipsilateral LGNd after visual cortex ablation) axon terminals with dense core vesicles appear exhibiting the structural peculiarities of growth cones seen during ontogenesis. They could be regarded as ultrastructural equivalent of the newly formed noradrenergic sprouts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2003

Interindividual and interspecies variations of the extrastriate visual cortex.

Functional homology between human and macaque visual cortices has provided an important cue to functional subdivisions of the human visual cortex, but it is unclear beyond V1. We estimated the sizes and the visual field eccentricity functions of the extrastriate visual areas of human brains using MRI and fMRI measurements to analyze the interindividual and interspecies variations. We found distinctive features of the area fraction values relative to V1 and the visual field eccentricity functions beyond V2 between the human and the macaque visual cortices. This suggests that selection on color-form and stereoscopic vision, associated with processing and manipulating socio-visual stimuli, may generate variations of the architecture of the extrastriate visual cortex beyond V2.

Adult↗

PubMed2006

MDMA use is associated with increased spatial BOLD fMRI visual cortex activation in human MDMA users.

Previous animal studies have demonstrated that 3,4-methylenedioxymethamphetamine (MDMA) exposure causes serotonin axotomy that is greatest in occipital cortex (including primary visual cortex) where serotonergic axons innervate neurons and blood vessels. Human MDMA users have altered serotonergic function and reduced gray matter density in occipital cortex. The fMRI BOLD method is potentially sensitive to both the neuronal and vascular consequences of MDMA-induced serotonin toxicity. To test the hypothesis that MDMA users have altered visual system function, we used the fMRI BOLD technique to assay visual cortical activation after photic stimulation in a group of adult MDMA users. Because MDMA users worldwide are polydrug users and therefore difficult to match to comparison groups in terms of polydrug exposure, we conducted a primary within-group analysis examining the correlation between lifetime episodes of MDMA exposure and measures of visual cortical activation. The within-group correlational analysis in the MDMA user group revealed that the degree of prior MDMA exposure was significantly positively correlated with the number of activated pixels for photic stimulation (r=0.582, p=0.007). A secondary between-group comparison of MDMA users with non-MDMA users found overall greater levels of polydrug exposure in the MDMA user cohort but no significant differences in visual cortical activation measures between the two groups. Additional research is needed to clarify the origin and significance of the current findings.

Adolescent↗

PubMed1975

Behavioral study of the visual cortex of Galago senegalensis.

An ablation study of the visual cortex of Galago senegalensis was undertaken in the hope of finding clues about the evolution of primate visual cortex. Removal of area 17 resulted in a profound sensory loss manifested by, first, the failure to discriminate between simple patterns; second, a deficit in localizing objects; third, a deficiency in tracking moving objects; and fourth, symptoms attributable to a deficiency in depth perception, such as misreaching and inaccurate jumping. Thus, the effects of ablating area 17 are similar in bushbabies and monkeys. In contrast, minimal sensory loss is produced by ablating area 17 in squirrels or tree shrews. This difference between primates and other mammals may depend on differences in the extent of the cortical target of the tecto-pulvinar path; in Galago and perhaps in all primates, more of the extrastriate visual cortex is entirely dependent on area 17. Removal of the ventral temporal cortex resulted in a loss of learned visual discriminations and in retardation in learning new visual discriminations. These symptoms seem related to the inferotemporal syndrome in monkeys.

Animals↗

PubMed1990

Arrangement of ocular dominance columns in human visual cortex.

The arrangement of the ocular dominance columns in the human primary visual cortex was studied by examining cytochrome oxidase activity in autopsy specimens of occipital lobes obtained from two patients who became blind in one eye before death. By artificially flattening the cortex before processing, it was possible to reconstruct the pattern formed by the ocular dominance columns throughout most of the primary visual cortex. The columns form a mosaic of irregular parallel stripes about 500 microns to 1000 microns wide (right eye column plus left eye column measures 1 to 2 mm), oriented at right angles to the boundary of the primary visual cortex. The columns are wider near the boundary of the primary visual cortex and within the representation of the peripheral visual field, the ocular dominance columns of the ipsilateral eye become fragmented until they disappear altogether at the border of the monocular crescent representation. The arrangement of ocular dominance columns in the human visual cortex is very similar to the pattern reported in the macaque monkey, although the columns in humans are wider.

Aged↗

PubMed2004

Localization of activity-dependent changes in blood volume to submillimeter-scale functional domains in cat visual cortex.

We have examined whether blood volume changes induced by neural activation are controlled precisely enough for us to visualize the submillimeter-scale functional structure in anesthetized and awake cat visual cortex. To activate the submillimeter-scale functional structures such as iso-orientation domains in the cortex, visual stimuli (gratings) were presented to the cats. Two methods were used to examine the spatial precision of blood volume changes including changes in total hemoglobin content and changes in plasma volume: (i) intrinsic signal imaging at the wavelength of hemoglobin's isosbestic point (569 nm) and (ii) imaging of absorption changes of an intravenously injected dye. Both measurements showed that the visual stimuli elicited stimulus-nonspecific and stimulus-specific blood volume changes in the cortex. The former was not spatially localized, while the latter was confined to iso-orientation domains. From the measurement of spatial separation of the iso-orientation domains, we estimated the spatial resolution of stimulus-specific blood volume changes to be as high as 0.6 mm. The changes in stimulus-nonspecific and -specific blood volume were not linearly correlated. These results suggest the existence of fine blood volume control mechanisms in the capillary bed in addition to global control mechanisms in arteries.

Anesthesia↗

PubMed1997

Visual cortex: a cat's-eye view of the visual system.

Optical imaging data show that the cat's visual cortex contains patches of cells that respond to low spatial and high temporal frequencies; outside the patches, cells respond to high spatial and low temporal frequencies. The results suggest a possible anatomical substrate for psychophysically defined spatial frequency channels.

Animals↗

PubMed1998

[Image processing in the primary visual cortex].

INTRODUCTION: Area 17 or the primary visual area forms the first link in the chain of cerebral analysis of a visual image. The neurones forming the primary visual cortex are characterized by the extreme precision of their connections, functional specialization and hierarchic organization. The spatial precision of the connections within the system for vision permit retinotopic representation in the visual cortex, so that each point of the retina is projected into a specific area of the cortex. The cortical neurones which analyze the characteristics of the image situated in a precise zone of the visual field are themselves organized into a basic functional unit known as a hypercolumn. Within each hypercolumn there are various columnar cell systems with receptive fields having similar characteristics. Thus, each hypercolumn is made up of multiple orientation columns, two ocular dominance columns and 'blob' regions. All these systems permit the analysis of different aspects of the image. The neurones belonging to the orientation columns are sensitive to the orientation, spatial frequency and movement of a visual stimulus; those of the 'blob' regions to colour, and the binocular neurones of the ocular dominance columns to depth. Within each column, the hierarchical pattern of neurone interconnections determines the successive appearance of cells with receptive fields having new properties.

Geniculate Bodies↗

PubMed1997

Spatio-temporal frequency domains and their relation to cytochrome oxidase staining in cat visual cortex.

Spatial and temporal frequencies are important attributes of the visual scene. It is a long-standing question whether these attributes are represented in a spatially organized way in cat primary visual cortex. Using optical imaging of intrinsic signals, we show here that grating stimuli of different spatial frequencies drifting at various speeds produce distinct activity patterns. Rather than observing a map of continuously changing spatial frequency preference across the cortical surface, we found only two distinct sets of domains, one preferring low spatial frequency and high speed, and the other high spatial frequency and low speed. We compared the arrangement of these spatio-temporal frequency domains with the cytochrome oxidase staining pattern, which, based on work in primate striate cortex, is thought to reflect the partition of the visual cortex into different processing streams. We found that the cytochrome oxidase blobs in cat striate cortex coincide with domains engaged in the processing of low spatial and high temporal frequency contents of the visual scene. Together with other recent results, our data suggest that spatiotemporal frequency domains are a manifestation of parallel streams in cat visual cortex, with distinct patterns of thalamic inputs and extrastriate projections.

Animals↗

PubMed1989

The development of basal forebrain projections to the rat visual cortex.

The development of the basal forebrain projections to the visual cortex of the rat were studied using retrograde tracer techniques. Injections of wheat germ agglutinin-horseradish peroxidase placed in the visual cortex of newborn animals resulted in labelling of neurons throughout the basal forebrain nuclei. Although at this time the overall distribution of retrogradely labelled cells within the basal forebrain appeared similar to that seen in the adult, cells were smaller and weakly stained. It was only at the end of the second postnatal week that the somata of stained neurons showed sizes and staining intensity comparable to the adult. This precedes or coincides with the reported significant increases in cortical and basal forebrain ChAT activity and the first detection of ChAT-labelled fibres in this cortical area. These data suggest an important developmental point around the end of the second postnatal week that may correspond to the time when a significant number of cholinergic axons first appear within the visual cortex. They also suggest that the cholinergic projections to the visual cortex develop late in comparison with the thalamic and other subcortical afferents in this cortical area.

Aging↗

PubMed2003

Activity-dependent change in the protein level of brain-derived neurotrophic factor but no change in other neurotrophins in the visual cortex of young and adult ferrets.

Neurotrophins are suggested to play a role in activity-dependent plasticity of visual cortex during the critical period of postnatal development. Thus, the concentration of neurotrophins in the cortex is expected to change with development and/or with alteration in neuronal activities. To test this, we measured protein levels of nerve growth factor, brain-derived neurotrophic factor, neurotrophin-3 and neurotrophin-4/5 in visual cortex of young (postnatal day 38-46, at the peak of the critical period) and adult ferrets with two-site enzyme-immunoassay systems. Measurements were carried out also in somatosensory cortex, hippocampus and cerebellum as control. With development the level of brain-derived neurotrophic factor did not significantly change, while those of the other neurotrophins changed in the visual cortex. A blockade of visual inputs for 24 h by an injection of tetrodotoxin into both eyes significantly decreased brain-derived neurotrophic factor protein level in the visual cortex, but not in the other regions in both young and adult ferrets. On the other hand, no significant decrease was seen in the protein level of the other neurotrophins in the visual cortex of young and adult ferrets. A monocular injection of tetrodotoxin in young ferrets resulted in the reduction of brain-derived neurotrophic factor by approximately half that by binocular injection. The degree of the decrease in the contralateral cortex to the injected eye was significantly larger than that in the ipsilateral cortex, reflecting that the contralateral eye is dominantly represented in the cortex in ferrets. Blockade of cortical neuronal activities by a GABA(A) receptor agonist led to a remarkable reduction of brain-derived neurotrophic factor protein in the visual cortex. These results suggest that the level of brain-derived neurotrophic factor protein in visual cortex is regulated by activities of cortical neurons.

Aging↗

PubMed1979

The rabbit and the cat: a comparison of some features of response properties of single cells in the primary visual cortex.

Receptive field characteristics of single cells in primary visual cortex of rabbit were studied. Seventy-two percent of cells were found to be orientation selective, and the remainder had concentric, uniform, movement selective or pure direction selective receptive fields. Single cells were also recorded from primary visual cortex of cat to permit a comparison of visual cortical organization in cats and rabbits. Laminar organization of receptive field types was observed in rabbits which was similar in most respects to that described in the cat. Although the major categories of orientation selective cells (simple, complex, hypercomplex) were similar for both cat and rabbit, many differences emerged: (I) tuning of orientation selectivity was narrower in cats than in rabbits; (II) units which preferred oblique orientations were less frequently represented in rabbits than in cats; (III) orientation preferences appeared to be arranged in clusters in rabbit cortex; in rabbits we found no evidence of the columnar organization of orientation selectivity which characterizes cat visual cortex. A comparison of our data with those previously reported for mouse, rat, hamster and opossum visual cortex suggest that mammals in which a significant proportion of visual cortical cells are not orientation selective have in common certain patterns of cortical organization involving a less precise and less specilized representation of stimulus orientation.

Animals↗

PubMed2000

Early postnatal development of functional ocular dominance columns in cat primary visual cortex.

During postnatal development of the visual cortex the thalamocortical afferents serving the two eyes segregate into alternating patches called ocular dominance (OD) columns. Interested in the dynamics of this segregation process we studied the appearance of functional OD columns in the primary visual cortex of normally raised and strabismic kittens aged 2-6 weeks using 2-deoxyglucose labelling in awake animals. In both experimental groups, OD columns covering the entire area 17 and spanning all cortical laminae are first visible at 3 weeks and appear already adult-like at 4 weeks, much earlier than thought on the basis of previous anatomical studies. We hypothesize that a small and anatomically undetectable imbalance between the afferents from the two eyes is amplified by intracortical interactions so that their activity patterns become different and may guide the segregation process of the afferents in cortical layer IV.

Afferent Pathways↗

PubMed1991

Isochronic transplantation of neonatal grafts in the visual cortex of cats: responsiveness, ocular dominance and specificity of cortical cells to visual stimulation.

The visual cortex of adult cats was studied physiologically following neonatal isochronic transplantation of grafts from areas 17,18, which were placed homotopically, in order to reveal their functional integration and thus possible repairing of damaged cortical neuronal circuits. Three homograft cats, in which transplantation was carried out between siblings (228 cortical cells) were compared to 4 animals receiving reimplanted autografts of the equivalent size (131 cells) as well as 3 animals with analogous sectioning of the visual cortex (162 cells) (pseudograft controls). The location of the boundaries between the transplant region and the host were determined using the Nissl's method for staining histological cross sections. Extracellular unit recording revealed typical waveform of the action potentials in the transplanted region and in the surrounding host tissue of all groups of cats. Visual responsiveness in the homograft cats was 17.5% in the transplanted region and 80.4% in the unoperated hemisphere; the corresponding results were 40.3% for the transplanted region and 82.2% for the unoperated hemisphere in the autografts and 23.1% and 73.4% in the pseudografts. The specificity of the cells to visual stimulation as expressed by their orientation and direction specificity, indicated preservation of these properties in the transplanted cats. While all responsive cells in the transplanted region of the homografts were orientation specific, their proportion was 60% in the autografts and 55.5% in the analogous region in the pseudograft controls. As to the direction specific cells, their performance in the grafted region of the grafted cats was even much higher than that of the pseudograft controls. The ocular dominance distribution of the cells showed preservation of binocularity in the transplanted region (90.0% binocular cells) of the homografts; it was however smaller in the equivalent region of the autografts (65.0%) and remarkably reduced (20.0%) in the pseudografts. It was concluded that despite the deafferentation induced during the transplantation procedure, a remarkable visual responsiveness was found in the transplanted region, indicating postoperative recovery. However, the cells there were mainly affected in their activity and less in their specificity to visual stimulation.

Animals↗

PubMed1987

Effects of neonatal monocular and binocular enucleation on transient acetylcholinesterase activity in developing rat visual cortex.

Geniculo-recipient layers of visual cortical area 17 in the laboratory rat display a transient pattern of acetylcholinesterase (AChE) activity during the second and third postnatal weeks of life. The appearance of the AChE histochemical reaction product and its distribution in thalamic recipient layers of cortical area 17 suggest that this transient AChE serves as a marker for the region of geniculocortical axon terminals. In the present study, infant rats were enucleated monocularly or binocularly on the day of birth. Animals were sacrificed at postnatal days 5-21. Frozen sections cut in either the transverse plane or parallel to the pial surface were processed for AChE histochemistry. Neonatal monocular enucleation resulted in a marked reduction of transient AChE activity in thalamic recipient layers of the medial part of area 17 contralateral to the enucleated orbit, i.e., the monocular segment of area 17. No loss of AChE was observed in area 17 ipsilateral to the enucleation. Pigmented and albino strains of rats did not differ significantly in the extent to which monocular enucleation reduced the transient AChE in contralateral visual cortex. Neonatal binocular enucleation resulted in an almost complete loss of AChE histochemical staining in thalamic recipient layers throughout cortical area 17, without loss of AChE in other cortical regions. These data support the hypothesis that transient AChE serves as a marker for the region of geniculocortical axon terminals, and also demonstrate that the transient expression of AChE in visual cortex depends upon normal innervation or activity of the geniculocortical neurons.

Acetylcholinesterase↗

PubMed1984

The monocular and binocular subfields of the rat's primary visual cortex: a quantitative morphological approach.

Primary visual cortex in the rat was studied by a variety of methods: transsynaptic transport of labelled amino acids, 2-deoxyglucose, and staining for perikarya, myelin, and acetylcholinesterase. The analysis was aided by a computer-controlled television image analyzer. The results obtained with different methods agree with one another in describing the position and extent of the entire primary visual cortex as well as its monocular (medial) and binocular (lateral) subareas.

Acetylcholinesterase↗

PubMed1989

Intraocular injections of tetrodotoxin reduce transiently expressed acetylcholinesterase activity in developing rat visual cortex.

Geniculo-recipient layers of primary visual cortex in the rat display a transient pattern of acetylcholinesterase (AChE) activity during the second postnatal week of life. Previous work has demonstrated that neonatal enucleations markedly reduce the transient AChE activity in visual cortex. The present studies were undertaken to determine the effects of reduced afferent neural activity on expression of the transient pattern of AChE activity. Rat pups received intraocular injections of tetrodotoxin (TTX) on postnatal days (PND) 3, 5, 7, 9 and 11 and were sacrificed on PND 12. Some animals were enucleated on PND 3. Brain sections were processed for AChE histochemistry and analyzed by optical densitometry. These experiments show that uniocular injections result in a markedly decreased level of AChE activity in layer IV of the medial part of cortical area 17 contralateral to the injected eye. The degree of reduction of AChE activity from repeated TTX injections was similar to the degree of reduction following enucleation on PND 3. Binocular injections of TTX result in a reduction of AChE activity in layer IV throughout cortical area 17, similar to the effects of binocular enucleation on PND 3. Experiments combining injection of horseradish peroxidase along with TTX on PND 11 demonstrate that retinal ganglion cells of TTX injected eyes are still capable of anterograde axonal transport. These data demonstrate that normal innervation and afferent activity are necessary for the transient expression of AChE activity by geniculocortical neurons.

Acetylcholinesterase↗