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PubMed2002

Extended plasticity of visual cortex in dark-reared animals may result from prolonged expression of cpg15-like genes.

cpg15 is an activity-regulated gene that encodes a membrane-bound ligand that coordinately regulates growth of apposing dendritic and axonal arbors and the maturation of their synapses. These properties make it an attractive candidate for participating in plasticity of the mammalian visual system. Here we compare cpg15 expression during normal development of the rat visual system with that seen in response to dark rearing, monocular blockade of retinal action potentials, or monocular deprivation. Our results show that the onset of cpg15 expression in the visual cortex is coincident with eye opening, and it increases until the peak of the critical period at postnatal day 28 (P28). This early expression is independent of both retinal activity and visual experience. After P28, a component of cpg15 expression in the visual cortex, lateral geniculate nucleus (LGN), and superior colliculus (SC) develops a progressively stronger dependence on retinally driven action potentials. Dark rearing does not affect cpg15 mRNA expression in the LGN and SC at any age, but it does significantly affect its expression in the visual cortex from the peak of the critical period and into adulthood. In dark-reared rats, the peak level of cpg15 expression in the visual cortex at P28 is lower than in controls. Rather than showing the normal decline with maturation, these levels are maintained in dark-reared animals. We suggest that the prolonged plasticity in the visual cortex that is seen in dark-reared animals may result from failure to downregulate genes such as cpg15 that could promote structural remodeling and synaptic maturation.

Action Potentials↗
PubMed2002

Orientation and color columns in monkey visual cortex.

The literature on orientation and color columns in monkey visual cortex is reviewed. The orientation column model most consistent with existing data is one containing 'stripes' of alternating positive and negative orientation 'singularities' (cytochrome oxidase blobs) which run along the centers of ocular dominance (OD) columns, with horizontal and vertical orientations alternating at interblob centers. Evidence is summarized suggesting that color is mapped continuously across the monkey's primary visual cortex, with the ends of the spectrum located at 'red' and 'blue' cytochrome oxidase blobs and extra-spectral purple located between adjacent red and blue blobs in the same OD column. In the orientation column model, the 'linear zones' of Obermayer and Blasdel have the appearance of the lines on a pumpkin. A pinwheel model of color columns, consistent with existing data, includes spectral and extra-spectral colors as spokes. Spectral iso-color lines run across iso-orientation lines in linear zones, while extra-spectral iso-color lines occupy the 'saddle points' of Obermayer and Blasdel. The color column model accounts for closure of the perceptual color circle, as proposed by Isaac Newton in 1704, but does not account for color opponency.

Animals↗
PubMed2004

Self-organization model of cytochrome oxidase blobs and ocular dominance columns in the primary visual cortex.

There are regularly arranged blobs that contain neurons labeled by cytochrome oxidase (CO) in the supragranular layer of the primary visual cortex (V1) of monkeys and cats. This theoretical study demonstrates that CO-blob-like patterns can be reproduced based on the thermodynamic model for the activity-dependent self-organization of afferent inputs from two different groups of neurons to the supragranular layer of the visual cortex. Computer simulation based on the model shows that within a particular parameter range each blob is centered in the ocular dominance (OD) band, as observed in macaque monkeys and galagos. Furthermore, by increasing the strength of correlation in activity between inputs from the two eyes, nearby blobs merge across OD borders, as seen in the cat visual cortex. Finally, for monocular deprivation, blobs in the deprived eyes shrink as observed in monkeys and cats. For binocular deprivation, less intensely labeled blobs were reproduced, while the blob density did not change as observed in monkeys.

Algorithms↗
PubMed1989

[The interaction of transcallosal and ascending excitation flows in the visual cortex of the cat].

The conformity of interhemispheric interaction in visual cortex were studied by means of EPs recordings in 10 immobilized cats under conditions of different time combinations of transcallosal and monocular stimulation of contra- or ipsilateral eyes. Phasic changes of the depression effects under transcallosal conditioning of facilitating effects under conditions of the model interaction similar to natural transcallosal interrelations, occurred in photostimulation of contralateral eye. Whereas the ipsilateral eye stimulation only depressed the time interaction under these conditions. The findings are discussed in terms of morphological, neurophysiological and other research data on transcallosal interhemispheric relations in the cat visual cortex. The 15-25-ms interval between heteromodal stimuli under these research conditions seem to correspond to natural conditions of transcallosal interhemispheric relations which, in binocular vision, are dynamically and topographically organized processes of excitation and inhibition.

Animals↗
PubMed1981

[Asymmetry of cat visual cortex potentials].

EPs in response to weak and strong stimuli at 200 points of visual cortex in both hemispheres were recorded in acute experiments on 80 anesthetized cats. Individual and species asymmetry of EP in visual cortex was characterized by its bilateral origin, mosaic localization and time stability. Transection of corpus callosum decreased a slight asymmetry and augmented a strong one. The interaction of endogenous and exogenous asymmetries augments the general asymmetry, particularly with a stimulus in a sagital plane. The data obtained suggest a hemispheric specialization in animals.

Animals↗
PubMed1999

Optical images of visible and invisible percepts in the primary visual cortex of primates.

We optically imaged a visual masking illusion in primary visual cortex (area V-1) of rhesus monkeys to ask whether activity in the early visual system more closely reflects the physical stimulus or the generated percept. Visual illusions can be a powerful way to address this question because they have the benefit of dissociating the stimulus from perception. We used an illusion in which a flickering target (a bar oriented in visual space) is rendered invisible by two counter-phase flickering bars, called masks, which flank and abut the target. The target and masks, when shown separately, each generated correlated activity on the surface of the cortex. During the illusory condition, however, optical signals generated in the cortex by the target disappeared although the image of the masks persisted. The optical image thus was correlated with perception but not with the physical stimulus.

Animals↗
PubMed1979

An electron microscope study of the early postnatal development of the visual cortex of the hooded rat.

Synaptic plasticity in response to environmental events has been clearly demonstrated in the visual cortex of the rat, but no detailed data concerning the course of early synaptogenesis in this area are available. In this study, synaptogenesis in the visual cortex of hooded rats at 1, 3, 5, 7 and 10 postnatal days of age (P1-P10) was examined with electron microscopy. The cortex was divided into the molecular layer, the superficial layers (II-IV) and deep layers (V-VI). In the visual cortex at P1, very few synapses are present in the molecular and deep layers and virtually none in the yet undifferentiated layers II-IV that compose the cortical plate at this age. The synapses that are present are axodendritic and often symmetrical with little membrane thickening and few vesicles. Axosomatic synapses were seen as early as P3 but very rarely. There are marked increases in axodendritic synaptic density and maturity with increasing age. By P7 and P10, many synapses appear mature in form and the majority can be classified a symmetrical. Axospinal synapses first appeared at P7 and were more frequent by P10. However, this classification was somewhat uncertain since no spinal apparatus was detected. Rate of synaptogenesis appeared to increase over the ages studied and showed no signs of leveling off except in the deep layers. Synaptic length was extremely variable and did not change systematically with age.

Age Factors↗
PubMed1982

Animal models of strabismic amblyopia: physiological studies of visual cortex and the lateral geniculate nucleus.

Receptive field properties of visual cortical and lateral geniculate cells were studied in 4 models of amblyopia in the cat: monocular deprivation (MD cats), surgical esotropia (esotropic cats), optically induced concomitant strabismus (stationary prism cats) and optically induced incomitant strabismus (rotating prism cats). Comparison observations were made in normal cats. Recordings in visual cortex indicated a reduction in responsiveness to the treated eye in MD and rotating prism cats. Esotropic and stationary prism cats showed mainly a loss of binocular cells. Recordings in the lateral geniculate nucleus indicated a reduction in the spatial resolving capacity of X-cells driven by the treated eye in MD, esotropic and rotating prism cats. The magnitude of this effect was comparable in all of these preparations. Stationary prism cats showed comparable spatial resolving capacities in X-cells driven by either eye. Y-cells were unaffected in any preparation except MD where there were reduced frequencies of Y-cells driven by the treated eye. These results indicate that: (1) interocular differences in spatial patterns without form deprivation are sufficient to produce a loss of responsiveness to one eye in visual cortex; (2) incomitant disparities are necessary to produce the physiological correlates of amblyopia in cats; and (3) deficits in spatial resolution in geniculate neurons are comparable in magnitude in various amblyopic preparations.

Amblyopia↗
PubMed1982

Central core control of developmental plasticity in the kitten visual cortex: I. Diencephalic lesions.

In five, dark-reared, 4-week-old kittens the posterior two thirds of the corpus callosum were split, and a lesion comprising the intralaminar nuclei was made of the left medial thalamic complex. In addition, the right eye was closed by suture. Post-operatively, the kittens showed abnormal orienting responses, neglecting visual stimuli presented in the hemifield contralateral to the side of the lesion. Sudden changes in light, sound, or somatosensory stimulation elicited orienting responses that all tended toward the side of the lesion. These massive symptoms faded within a few weeks but the kittens continued to neglect visual stimuli in the hemifield contralateral to the lesion when a second stimulus was presented simultaneously in the other hemifield. Electrophysiologic analysis of the visual cortex, performed after the end of the critical period, revealed marked interhemispheric differences. In the visual cortex of the normal hemisphere most neurons were monocular and responded exclusively to stimulation of the open eye, but otherwise had normal receptive field properties. In the visual cortex of the hemisphere containing the thalamic lesion, the majority of the neurons remained binocular. In addition, the selectivity for stimulus orientation and the vigor of responses to optimally aligned stimuli were subnormal on this side. Thus, the same retinal signals, which in the control hemisphere suppressed the pathways from the deprived eye and supported the development of normal receptive fields, failed to do either in the hemisphere containing the thalamic lesion. Apparently, experience-dependent changes in the visual cortex require both retinal stimulation and the functioning of diencephalic structures which modulate cortical excitability and control selective attention.

Animals↗
PubMed2003

The spatial pattern of response magnitude and selectivity for orientation and direction in cat visual cortex.

Optical imaging studies of orientation and direction preference in visual cortex have typically used vector averaging to obtain angle and magnitude maps. This method has shown half-rotation orientation singularities (pinwheels) located within regions of low orientation vector magnitude. Direction preference is generally orthogonal to orientation preference, but often deviates from this, particularly in regions of low direction vector magnitude. Linear regions of rapid change in direction preference terminate in or near orientation singularities. The vector-averaging method is problematic however because it does not clearly disambiguate spatial variation in orientation tuning width from variation in height. It may also wrongly estimate preferred direction in regions where preference is weak. In this paper we analyze optical maps of cat visual cortex by fitting model tuning functions to the responses. This new method reveals features not previously evident. Orientation tuning height and width vary independently across the map: tuning height is always low near singularities, however regions of broad and narrow orientation tuning width can be found in regions of low tuning height, often alternating in a spoke-like fashion around singularities. Orientation and direction preference angles are always closely orthogonal. Reversals in direction preference form lines that originate precisely in orientation singularities.

Animals↗
PubMed1987

Nicotine receptors are located on lateral geniculate nucleus terminals in cat visual cortex.

Using the methods of in vitro receptor autoradiography, we have characterized a population of receptors for nicotine in cat visual cortex that is concentrated primarily in layer IV of areas 17 and 18. Surgically undercutting the visual cortex essentially abolished [3H]nicotine binding in the isolated zone. However, neuron-specific, quinolinic acid lesions of a region of visual cortex had little effect on binding, establishing a presynaptic locus on cortical inputs for these sites. Lesions of the lateral geniculate nucleus abolished binding in the corresponding cortical areas, thus localizing the [3H]nicotine binding sites to lateral geniculate nucleus terminals in the cortex.

Animals↗
PubMed2006

Opposite dependencies on visual motion coherence in human area MT+ and early visual cortex.

In order to understand the relationship between brain activity and visual motion perception, knowledge of the cortical areas participating in signal processing alone is insufficient. Rather knowledge on how responses vary with the characteristics of visual motion is necessary. In this study, we measured whole brain activity using magnetoencephalography in humans discriminating the global motion direction of a random dot kinematogram whose strength was systematically varied by the percentage of coherently moving dot elements. Spectral analysis revealed 2 components correlating with motion coherence. A first component in the low-frequency domain ( approximately 3 Hz), linearly increasing with motion coherence, could be attributed to visual cortex including human area middle temporal (MT) +. A second component oscillating in the alpha frequency range and emerging after stimulus offset showed the inverse dependence on motion coherence and arose from early visual cortex. Based on these results, we first of all conclude that motion coherence is reflected in the population response of human extrastriate cortex. Second, we suggest that the occipital alpha activity represents a gating mechanism protecting visual motion integration in later cortical areas from disturbing upcoming signals.

Adult↗
PubMed1988

Developmental changes of the distribution of binding sites for organic Ca2+-channel blockers in cat visual cortex.

There are indications that during a critical period of visual cortex development Ca2+-fluxes from extra- to intracellular compartments serve as a trigger signal for experience-dependent changes of neuronal response properties. In this study we investigate the possibility of a relation between the time course of the critical period and age-dependent changes in the density and topographical distribution of Ca2+-channels. As a marker for the latter we used Ca2+-channel blockers of the 1,4-Dihydropyridine (1,4-DHP) class since these are supposed to bind to voltage-dependent Ca2+-channels. We used the tritiated 1,4-DHP derivative 3H-PN 200 110 for autoradiographic determination of 1,4-DHP binding sites in the visual cortex of adult cats and kittens ranging in age from two to ten weeks. The binding of 3H-PN 200 110 to slide-mounted tissue sections was saturable and of high affinity. The overall density of specific 3H-PN 200 110 binding sites decreased during development and their laminar distribution underwent marked changes: in young kittens specific binding was accentuated in lower layer IV, whereas in adult cats the supragranular layers were most intensely labeled. Dark rearing did not affect these developmental changes of 3H-PN 200 110 binding sites. The time course of the reduction of 1,4-DHP binding sites correlates well with that of the age-dependent decrease of the susceptibility to experience-dependent modifications. We consider this result as compatible with the hypothesis that use-dependent modifications of the response properties of cortical neurons involve changes in the Ca2+-fluxes from extra- to intracellular compartments.

Aging↗
PubMed2001

Modulation of sensory suppression: implications for receptive field sizes in the human visual cortex.

Neurophysiological studies in monkeys show that when multiple visual stimuli appear simultaneously in the visual field, they are not processed independently, but rather interact in a mutually suppressive way. This suggests that multiple stimuli compete for neural representation. Consistent with this notion, we have previously found in humans that functional magnetic resonance imaging (fMRI) signals in V1 and ventral extrastriate areas V2, V4, and TEO are smaller for simultaneously presented (i.e., competing) stimuli than for the same stimuli presented sequentially (i.e., not competing). Here we report that suppressive interactions between stimuli are also present in dorsal extrastriate areas V3A and MT, and we compare these interactions to those in areas V1 through TEO. To exclude the possibility that the differences in responses to simultaneously and sequentially presented stimuli were due to differences in the number of transient onsets, we tested for suppressive interactions in area V4, in an experiment that held constant the number of transient onsets. We found that the fMRI response to a stimulus in the upper visual field was suppressed by the presence of nearby stimuli in the lower visual field. Further, we excluded the possibility that the greater fMRI responses to sequential compared with simultaneous presentations were due to exogeneous attentional cueing by having our subjects count T's or L's at fixation, an attentionally demanding task. Behavioral testing demonstrated that neither condition interfered with performance of the T/L task. Our previous findings suggested that suppressive interactions among nearby stimuli in areas V1 through TEO were scaled to the receptive field (RF) sizes of neurons in those areas. Here we tested this idea by parametrically varying the spatial separation among stimuli in the display. Display sizes ranged from 2 x 2 degrees to 7 x 7 degrees and were centered at 5.5 degrees eccentricity. Based on the effects of display size on the magnitude of suppressive interactions, we estimated that RF sizes at an eccentricity of 5.5 degrees were <2 degrees in V1, 2-4 degrees in V2, 4-6 degrees in V4, larger than 7 degrees (but still confined to a quadrant) in TEO, and larger than 6 degrees (confined to a quadrant) in V3A. These estimates of RF sizes in human visual cortex are strikingly similar to those measured in physiological mapping studies in the homologous visual areas in monkeys.

Adult↗
PubMed1992

[The effect of early partial postnatal deafferentation of the visual cortex on synapse formation].

A quantitative analysis of the synaptic population of the upper layers of the visual cortex of mice Acomys cahirinus has shown that the process of postnatal synaptogenesis proceeds during all the period of observations (1-13 days), the intensity of morphological differentiation of various types of synapses being higher during the first 5 days of life. Partial deafferentation of the visual cortex (dissection of the corpus callosum) in 3-, 5- and 13-day-old Acomyses results in changes of synapses of the II-III layers of the visual cortex of adult animals--with age of the operated animals the number of types of synapses, where quantitative morphological changes are observed, decreases. Thus, there exists a correlation between the maturity of synaptic population at the moment of damaging and the character of ultrastructural changes in response to this damage.

Afferent Pathways↗
PubMed2002

Spatial structure and symmetry of simple-cell receptive fields in macaque primary visual cortex.

I present measurements of the spatial structure of simple-cell receptive fields in macaque primary visual cortex (area V1). Similar to previous findings in cat area 17, the spatial profile of simple-cell receptive fields in the macaque is well described by two-dimensional Gabor functions. A population analysis reveals that the distribution of spatial profiles in primary visual cortex lies approximately on a one-parameter family of filter shapes. Surprisingly, the receptive fields cluster into even- and odd-symmetry classes with a tendency for neurons that are well tuned in orientation and spatial frequency to have odd-symmetric receptive fields. The filter shapes predicted by two recent theories of simple-cell receptive field function, independent component analysis and sparse coding, are compared with the data. Both theories predict receptive fields with a larger number of subfields than observed in the experimental data. In addition, these theories do not generate receptive fields that are broadly tuned in orientation and low-pass in spatial frequency, which are commonly seen in monkey V1. The implications of these results for our understanding of image coding and representation in primary visual cortex are discussed.

Animals↗
PubMed2002

[Arteries of visual cortex].

The purpose of the study was to point out the arterial branches that are supplying the visual cortex. This study was carried out on 100 brains, fixed in formaldehid 10% and dissected under the surgical microscope; 20 of them were at first injected with colored nitrolac. It was observed the origin, relationships and distribution of the arterial branches, which supply these areas. The data obtained reveal that: medial face of the visual cortex receives branches from the posterior cerebral artery (throughout its collaterals: calcarine artery 100%, parietooccipital artery 96% and posterior temporal artery 92%; its lateral surface receives cortical branches from the middle cerebral artery (100%) and its inferior surface is irigated from collaterals of the posterior temporal and temporo-occipital arteries (100%). Some of the branches penetrate directly the visual cortex perpendiculary and others form at first, a superficial, pial network. The knowledge of arterial variants which supply the visual areas is very important for ophthalmologists, radiologists, neuroophthalmologists, neurosurgeons, for recognising their vascular damage in some complex neuroophthalmologic syndroms.

Autopsy↗
PubMed2004

Regular structural organization of intrahemisphere interzonal connections in the visual cortex of the cat.

The aim of the present work was to conduct a morphometric analysis of the cluster organization of neurons forming interzonal corticocortical connections in the visual cortex. The investigations used a method based on retrograde transport of horseradish peroxidase and mathematical analysis of the spatial distribution of labeled cells. Measurements yielded the following quantitative characteristics of the cell distribution--the volume and linear sizes of clusters, the distance between the centers of gravity of clusters, and the periodicity in the distribution of clusters along the cortical surface. Age-related features of the distribution of cells giving rise to cortical interzonal connections were identified. The experiments showed that the pattern of the cluster organization typical of adult cats was formed by the end of the second month of life. Quantitative differences in the spatial organization of neuron groups in the cortex of visual fields 17 and 18 were demonstrated.

Age Factors↗