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PubMed1983

[Characteristics of the coding of light stimulus intensity by visual cortex neurons during light adaptation in the cat].

Response of 70 neurons in area 17 of the visual cortex to optimal stimuli of different intensity in the receptive field under conditions of photopic adaptation were analyzed in unanesthetized cats. The reaction threshold, differential sensitivity, optimal intensity and the width of the brightness range were estimated. No intensity detectors were found in this area. 70% of neurons studied had inhibitory distortion in the range of their intensity functions. The neurons differed in their threshold reactions by 5-6 orders, in dynamic range--by 3-4 orders, and in differential sensitivity--by 2-3 orders. The visual cortex neurons with receptive fields in central and periphery parts of the visual field had different intensity functions.

Animals↗

PubMed1996

Development of orientation preference maps in ferret primary visual cortex.

The development of orientation preference maps was studied in ferret primary visual cortex using chronic optical imaging of intrinsic signals. The emergence and maturation of the maps were examined over time in single animals. The earliest age at which cortical domains selectively responsive to particular stimulus orientations were observed varied considerably between individuals, from postnatal day 31 to 36. In all cases, the earliest maps seen were low-contrast, with regions of orientation-specific activity that were difficult to distinguish from noise. These early maps matured over a period of several days into the high-contrast, patchy maps typical of adult animals. The structure of the orientation maps was remarkably constant over time. The indistinct features in the earliest maps were always patches of the same sizes and shapes and at the same locations as in the maps obtained in subsequent recording sessions. Details of the more mature maps, including the relative intensities of individual iso-orientation domains, were also constant from one recording session to another over periods of several weeks. The patterning of iso-orientation domains in ferret primary visual cortex thus is established early in development and remains stable over time, unaffected by either normal visual experience or the anatomical rearrangements of geniculocortical afferents into eye-specific domains.

Age Distribution↗

PubMed1999

Effects of hyperoxia and hypocapnia on regional venous oxygen saturation in the primary visual cortex in conscious humans.

Hyperoxia can improve oxygen delivery in patients exposed to hypocapnia for neurosurgical procedures but this effect may be modified by regional differences in the degree of hypocapnic vasoconstriction. Using functional magnet resonance imaging (fMRI), we have investigated the influence of hyperoxia on blood flow and blood oxygenation in the primary visual cortex in hypocapnic volunteers. Consecutive fMRI measurements were performed in 10 awake, male volunteers during hypocapnia (mean PE'CO2 3.3 (SD 0.1) kPa) and normocapnia (PE'CO2 5.3 (0.1) kPa) at FIO2 values of 0.21 and 1.0, respectively. Hypocapnia significantly reduced the pixel count in the primary visual cortex (median 169 (quartiles 34-246) vs 21 (0-40) pixels at an FIO2 of 0.21). Additional hyperoxia had no influence on this reduction in pixel count (16 (0-28) pixels at FIO2 1.0 vs 21 (0-40) pixels at FIO2 0.21). Hyperoxia did not influence hypocapnic vasoconstriction in the primary visual cortex. These data suggest that in the primary visual cortex, administration of oxygen alone may not be sufficient to improve oxygen delivery under hypocapnic conditions.

Adult↗

PubMed2000

Pre-attentive segmentation in the primary visual cortex.

The activities of neurons in primary visual cortex have been shown to be significantly influenced by stimuli outside their classical receptive fields. We propose that these contextual influences serve pre-attentive visual segmentation by causing relatively higher neural responses to important or conspicuous image locations, making them more salient for perceptual pop-out. These locations include boundaries between regions, smooth contours, and pop-out targets against backgrounds. The mark of these locations is the breakdown of spatial homogeneity in the input. for instance, at the border between two texture regions of equal mean luminance. This breakdown causes changes in contextual influences, often resulting in higher responses at the border than at surrounding locations. This proposal is implemented in a biologically based model of VI in which contextual influences are mediated by intra-cortical horizontal connections. The behavior of the model is demonstrated using examples of texture segmentation, figure-ground segregation, target-distractor asymmetry, and contour enhancement, and is compared with psychophysical and physiological data. The model predicts (1) how neural responses should be tuned to the orientation of nearby texture borders, (2) a set of qualitative constraints on the structure of the intracortical connections, and (3) stimulus-dependent biases in estimating the locations of the region borders by pre-attentive vision.

Form Perception↗

PubMed1999

Induction of NMDA receptor-dependent long-term depression in visual cortex does not require metabotropic glutamate receptors.

We tested the role of group I mGluRs in the induction of long-term depression (LTD) in the visual cortex, using the novel mGluR antagonist LY341495 and mice lacking mGluR5, the predominant phosphoinositide (PI)-linked mGluR in the visual cortex. We find that LY341495 is a potent blocker of glutamate-stimulated PI hydrolysis in visual cortical synaptoneurosomes, and that it effectively antagonizes the actions of the mGluR agonist 1S, 3R-aminocyclopentane-1,3-dicarboxylic acid (ACPD) on synaptic transmission in visual cortical slices. However, LY341495 has no effect on the induction of LTD by low-frequency stimulation. Furthermore, mice lacking mGluR5 show normal NMDA receptor-dependent LTD. These results indicate that group I mGluR activation is not required for the induction of NMDA receptor-dependent LTD in the visual cortex.

Amino Acids↗

PubMed2001

The neural basis of biased competition in human visual cortex.

A typical scene contains many different objects that compete for neural representation due to the limited processing capacity of the visual system. At the neural level, competition among multiple stimuli is evidenced by the mutual suppression of their visually evoked responses and occurs most strongly at the level of the receptive field. The competition among multiple objects can be biased by both bottom-up sensory-driven mechanisms and top-down influences, such as selective attention. Functional brain imaging studies reveal that biasing signals due to selective attention can modulate neural activity in visual cortex not only in the presence, but also in the absence of visual stimulation. Although the competition among stimuli for representation is ultimately resolved within visual cortex, the source of top-down biasing signals likely derives from a distributed network of areas in frontal and parietal cortex. Attention-related activity in frontal and parietal areas does not reflect attentional modulation of visually evoked responses, but rather the attentional operations themselves.

Evoked Potentials, Visual↗

PubMedDate not supplied

[Responses of visual cortex neurons to photic and acoustic stimuli in rabbits reared in the dark].

Unit responses in the visual cortex to photic and acoustic stimuli were studied in intact and visually deprived rabbits raised in the dark since birth up to 2.5--5 months of age. Photic flashes, tones, single and rhythmical clicks were used as stimuli. A significant increase of the number of bimodal units was revealed in the cortex of visually deprived rabbits. The level of significance of the statistical estimate of the change in the number of phonoreactive units (its increase due to deprivation) amounts to 92%. The nature of responses to flashes and the ratio of photoreactive units does not change due to deprivation, which suggests their genetic determination. Possible mechanisms of the re-distribution of neuronal reactivity in the rabbit visual cortex in conditions of deprivation are discussed.

Animals↗

PubMed1996

A dynamic and quantitative study of pattern visual evoked potentials and gamma-aminobutyric acid neurones in the lateral geniculate nucleus and the visual cortex of monocular deprivation cats.

PURPOSE: To assess the effects of monocular lid closure during critical period on cortical activity. METHOD: Pattern visual evoked potentials (PVEP) of the normal and the monocular deprivation (MD) cats were dynamically measured and the number of gammaaminobutyric acid immunopositive (GABA-IP) neurones of the area 17 of the visual cortex and the lateral geniculate nucleus (LGN) was quantitatively compared by using immunohistochemical method (ABC). RESULTS: The amplitude of the N1-P1 attenuated in deprived eyes (DE), NE/DE at postnatal week (PNW) 7-8 (P < 0.05), NE/DE at PNW 15-16 (P < 0.01); while P1 latency delayed, NE/DE at PNW 7-8 (P > 0.05), NE/DE at PNW 15-16 (P< 0.05). The numbers of GABA-IP neurones in layer A1 of the ipsilateral LGN and in layer A of the contralateral LGN, compared to those in the corresponding normal laminae, were not significant at PNW 7-8 and PNW 11-12 (P > 0.05), while in the same cats a reduction in the number of GABA-IP neurones was found in layer IV of area 17 at PNW 11-12 (P < 0.05). However, with longer survival of 3-4 weeks in duration, the numbers of GABA-IP neurones in the deprived laminae of LGN were remarkably reduced (P < 0.05). CONCLUSIONS: The amplitude of N1-P1 components is sensitive to the effects of monocular deprivation. Monocular deprivation in cats during critical period leads to dramatic changes of the number of GABA-IP neurones in the LGN and cortical layer IV receiving inputs from the deprived eye in cats. The deprivation-induced reduction in GABA-IP neurones is delayed in the LGN compared with the visual cortex. PVEP of the MD cats is consistent with the damage of its GABA system in visual cortex.

Animals↗

PubMed1991

Significant non-serotonergic raphe projection to the visual cortex of the rat. An immunohistochemical study combined with retrograde tracing.

The present study investigated the distribution of serotonergic and non-serotonergic raphe neurons with direct projections to the visual cortex. The study employed the WGA-apoHRP-Au retrograde transport technique combined with 5-HT immunohistochemical staining. Retrogradely labeled cells were observed in the dorsal raphe nucleus, the median raphe nucleus, and in the B9 and B6 cell groups. One notable finding was the great number of retrogradely labeled, non-5-HT immunoreactive cells. The average percentages of such cells in the various raphe regions were as follows: DR: 52% (n = 401); MR: 35% (n = 311); B9: 24% (n = 129); B6: 95% (n = 200). The present study demonstrated the presence of a significant proportion of non-serotonergic raphe region neurons projecting to the primary visual cortex in the rat. It is suggested that these neurons may complement the aminergic neurons as part of the ascending system which controls the functions of the visual cortex.

Animals↗

PubMed1983

Effect of eye rotation on visual-field map onto superior colliculus and visual cortex.

We used multiunit recording to assess the effect of rotating one eye approximately 90 degrees at about the time of normal eye opening. Rotation of the eye did not alter the topography of the retinal maps onto visual cortex or superior colliculus. The intorted eye drove cells at most recording points in the contralateral visual cortex and superior colliculus. In its ipsilateral colliculus the intorted eye drove cells at about 10% of the recording points; that is, the temporal retina of this eye was quite ineffective in driving collicular cells. In its ipsilateral cortex the intorted eye drove cells at about 30% of the recording sites. The unoperated eye drove cells at all locations in both colliculus and cortex on both sides of the brain. The effects of extorsion were studied only in the superior colliculus. Extorsion and intorsion produced similar results except that extorsion produced a less severe deficit in the ability of the temporal retina to drive cells in its ipsilateral colliculus. Cutting all the extraocular muscles without eye rotation was studied only in the colliculus and produced results similar to those produced by intorsion and extorsion. However, the temporal retina of the operated eye was more effective after muscle cut alone than after intorsion or extorsion. Forcing the animal to use the rotated right eye alone on alternate days during the first 3 mo of life did not decrease the deficits. Almost all recording sites in the right colliculus were driven only by the unoperated left eye. If the left eye was sutured when the right eye was rotated, only the right eye drove cells in the left colliculus, but the two eyes were about equally effective in the right colliculus; however, rather few sites in the right colliculus were binocularly driven. We conclude that both extraocular muscle section and eye rotation reduce the effectiveness of the uncrossed input from the operated eye to the superior colliculus and visual cortex. The effects on the superior colliculus are, however, greater.

Animals↗

PubMed1999

Restoration of ocular dominance plasticity mediated by adenosine 3',5'-monophosphate in adult visual cortex.

Noradrenaline (NA)-stimulated beta-adrenoreceptors activate adenylate cyclase via excitatory G-proteins (Gs). Activated adenylate cyclase in turn promotes the production of cAMP. Critical roles of cAMP-dependent protein kinase A (PKA) in divergent cellular functions have been shown, including memory, learning and neural plasticity. Ocular dominance plasticity (ODP) is strongly expressed in early postnatal life and usually absent in the mature visual cortex. Here, we asked whether the activation of cAMP-dependent PKA could restore ODP to the aplastic visual cortex of adult cats. Concurrent with brief monocular deprivation, each of the following cAMP-related drugs was directly and continuously infused in the adult visual cortex: cholera toxin (a Gs-protein stimulant), forskolin (a Gs-protein-independent activator of adenylate cyclase) and dibutyryl cAMP (a cAMP analogue). We found that the ocular dominance distribution became W-shaped, the proportion of binocular cells being significantly lower than that in respective controls. We concluded that the activation of cAMP cascades rapidly restores ODP to the adult visual cortex, though moderately. The finding further extends the original hypothesis that the NA-beta-adrenoreceptors system is a neurochemical mechanism of cortical plasticity.

Animals↗

PubMed1990

Formation of target-specific neuronal projections in organotypic slice cultures from rat visual cortex.

A characteristic feature of the mammalian cortex is that projection neurons located in distinct cortical layers send their axons to different targets. In visual cortex, cells in layers 2 and 3 project to other cortical areas, whereas cells in layers 5 and 6 project to subcortical targets such as the lateral geniculate nucleus. The proper development of these projections is crucial for correct functioning of the visual system. Here we show that specific connections are established in an organotypic culture system in which rat visual cortex slices are co-cultured with another slice of the visual cortex or with a thalamic slice. The laminar origin and cellular morphology in vitro of cortical projections to other cortical regions or to subcortical targets are remarkably similar to those seen in vivo. In addition, axons of projecting cells are not restricted to particular pathways, but appear instead to grow directly towards their appropriate target. These observations raise the possibility that chemotropic attraction from the target areas may play an important part in the development of the cortical projection pattern.

Afferent Pathways↗

PubMed2002

The distribution and morphology of calbindin D28K- and calretinin-immunoreactive neurons in the visual cortex of mouse.

We studied the distribution and morphology of calbindin D28K- and calretinin-immunoreactive (IR) neurons in the mouse visual cortex with immunocytochemistry. Most of the calbindin D28K-IR neurons were located in layers II/III and V, while calretinin-IR neurons were predominantly located in layers II/III. The labeled neurons showed variations in morphology. The majority of the calbindin D28K-IR neurons were stellate and round or oval cells with multipolar dendrites. The majority of calretinin-IR neurons were vertical fusiform cells with long processes traveling perpendicular to the pial surface. In the mouse visual cortex, 20.2% of calbindin D28K-IR neurons contained calretinin and 27.2% of calretinin-IR neurons contained calbindin D28K. These results indicate that the calcium-binding proteins, calbindin D28K and calretinin are distributed in specific layers and in selective cell types of the mouse visual cortex.

Animals↗

PubMed1995

Sustained inhibition of acetylcholinesterase activity does not disrupt early geniculocortical ingrowth to developing rat visual cortex.

Esterase activity of endogenous transiently expressed acetylcholinesterase was locally suppressed in visual cortex of infant rats for 2-5 days by the irreversible inhibitor phospholine iodide, delivered from Elvax implants. Tissue processed for anterograde movement of the carbocyanine dye DiI or anterograde transneuronal transport of wheat germ agglutinin-horseradish peroxidase revealed normal geniculocortical growth into layer IV of visual cortex. These results suggest that the catalytic activity of transiently expressed acetylcholinesterase may play little, if any, role in early development of thalamocortical systems.

Animals↗

PubMed1995

Distribution and density of monoamine receptors in the primate visual cortex devoid of retinal input from early embryonic stages.

Developmental mechanisms that regulate the areal and laminar distribution of various macromolecules, including neurotransmitter receptors in the cerebral cortex, are not known. In the present study, we examined the development of monoaminergic receptors in the rhesus monkey striate and peristriate visual cortex in the absence of input from the retina. Binocular enucleation was performed between embryonic days E60 and E81, prior to the ingrowth of geniculocortical fibers into the cortical plate and before genesis of the granular and supragranular layers of the visual cortex. The animals were delivered at term (E165) and sacrificed at 2 or 12 months of age, and their brains frozen and the occipital lobes cut at 20 microns in the coronal plane. Cortical binding of 3H-clonidine, 125I-pindolol, 3H-5-HT, 3H-ketanserin, 3H-spiperone, 3H-SCH23390, and 3H-prazosin that label various monoamine receptors were autoradiographically visualized and quantified using a computer imaging system. All radioligands displayed specific laminar patterns in the striate and prestriate areas in both groups of animals. The areal and laminar distribution in the anophthalmic monkeys was similar to that in the controls. Significantly, in all enucleated animals, just as in the controls, a particularly high density of 3H-clonidine and 3H-prazosin was observed in the sublayers of layer IV involved in color vision. The present results show that the monoamine receptors in primate visual cortex can establish and maintain distinct laminar and areal patterns in the absence of activity or molecular cues originated from the retina, and provide new insight into the cortical consequences of secondary congenital anophthalmia.

Animals↗

PubMed1997

Radiation-induced, lamina-specific deletion of neurons in the primate visual cortex.

To examine the early determinants of cortical cytoarchitecture, we deleted specific neuronal classes in the primate visual cortex by ionizing irradiation at selected prenatal stages. Multiple doses of X-rays were delivered to the macaque monkey brain between embryonic day (E) 80 and E90 to block the division of cells destined to populate the superficial cortical layers, between E70 and E79 to eliminate neurons destined for the middle layers; and between E33 and E40 to delete neurons destined for the lateral geniculate nucleus (LGN) that project to the cortex. All animals were killed after birth, and their brains were processed for histological and electron microscopic analyses. Cell density and number in the LGN and visual cortex were determined by using three-dimensional, computer-aided morphometry. In animals irradiated with low doses (total of approximately 200 cGy) during the genesis of the LGN but before the onset of corticogenesis (E33-40), the LGN was reduced in both volume and number of neurons. Area 17 in these animals displayed only slight changes in cortical thickness, cell density, and area-specific cytoarchitectonic features, whereas the total surface devoted to area 17 was significantly diminished. In contrast, animals irradiated with low doses during the period of corticogenesis, after the completion of the LGN genesis, showed no significant change in the volume of the LGN or in the number of its cells. Moreover, in these animals, the surface of area 17 was not significantly altered, although the cortical layers generated at the time of irradiation had a significantly lower density and total number of cells, whereas the layers generated before and after the period of irradiation were spared. In contrast, cases exposed to high doses of X-ray (total > 300 cGy) showed more severe effects, including all layers. However, layers normally generated during irradiation were depleted and consisted of cell-sparse strata populated by densely packed neuropil (axons, small dendrites, dendritic spines, and synaptic boutons). These cell-sparse strata were situated deeper in the early irradiated animals than in the later irradiated animals, and their laminar position changed abruptly at the area 17/18 border. These results show that low doses of irradiation in a slowly developing primate brain can be used effectively to eliminate targeted classes of neurons before they reach their final position, providing an opportunity to examine the role of cell-cell interactions in the formation of circuitry and the role of specific cell classes in cortical development.

Animals↗

PubMed1985

Golgi and Nissl studies of the visual cortex of the bottlenose dolphin.

Nissl, Golgi and fibre preparations were made of the cerebral cortex of the lateral gyrus of the bottlenose dolphin (Tursiops truncatus) in the region where visual evoked potentials have been reported (Sokolov et al., '72; Ladygina et al., '78). In the adult the visual cortex is relatively thin (average about 1,300 micron) for so large a brain (fixed brain weight for a typical adult in our series was 1,330 g). Layers I, III, and VI are wide and represent three-quarters of the total cortical thickness. Layer I contains few cell bodies, while III and VI have a variety of pyramidal and nonpyramidal neurons. Layers II and V are narrow and contain striking palisades of darkly staining pyramidal cells that are particularly large in layer V. No clearly demarcated layer IV is present in the adult dolphin visual cortex. Many of the neurons identified with the Golgi technique are typical of pyramids in other mammals, with a single apical dendrite and a bouquet of basal dendrites, mostly highly spiny. Others are unusual in having bifurcated or oblique apical dendrites. Typical large and small spiny and nonspiny stellates are also found, mainly in layers III and VI. In addition various forms of spindle-shaped, bipolar and multipolar neurons are found in most layers. An 18-day-old brain shows signs of immaturity in its visual cortex. It is thinner (970 micron) and on average its neurons are smaller, paler, and more densely packed. Especially the pyramids of layer V are much smaller than in the adult. Also, a distinct "granular" band occurs between layers III and V and seems to be a rudimentary layer IV. At 3 years of age most of the adult features have developed, but layer IV is still detectable. No striking differences were observed in cell and fibre architecture between the cortex of the lateral gyrus and that of the so-called "calcarine" area that has also been considered as "visual." We concluded that, although different in many respects from other mammalian visual cortices, that of the dolphin is apparently well developed and differentiated.

Aging↗

PubMed1988

Corpus callosum transection reduces binocularity of cells in the visual cortex of adult cats.

The possible involvement of the corpus callosum in binocular functions of the visual cortex was studied in adult cats. Unit recording was made in areas 17, 18 boundary following posterior or complete transection of the corpus callosum, acutely as well as chronically, after short (3-4 months) and long (5.5-39 months) survival periods. A considerable reduction of binocularly driven cells was found in the posteriorly callosally transected cats (acute: 41% cells; short-chronic: 65%; long-chronic: 32%). Similar results, albeit smaller in the long-survival group, were found following complete callosal transection. In comparison, the proportion of binocular cells in the normal cats was 85%. It was concluded that the corpus callosum is involved in interhemispheric integration and enhancement of binocularity in visual cortex cells. No recovery occurs as function of time following cancellation of the interhemispheric interaction by callosal transection.

Animals↗