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PubMed1997

Transplant of polymer-encapsulated cells genetically engineered to release nerve growth factor allows a normal functional development of the visual cortex in dark-reared rats.

Visual experience is necessary for the normal development of the visual system. Dark-reared mammals show abnormal vision when reintroduced into a normal environment. The absence of visual experience during the critical period results in reduced and/or inappropriate neural responses in visual cortical neurons. The change in electrical activity induced by dark rearing is probably reflected by the modulation of specific unknown molecules. Neurotrophins are present in the developing visual cortex and their production depends on visually driven electrical activity. Recent findings support the possibility that an important link between electrical activity in the visual pathway and correct development of visual properties is represented by neurotrophins. We advance the hypothesis that the visual abnormalities present in dark-reared animals could be due to a decreased production of a neurotrophin secondary to the lack of visual stimulation. We report that some properties of visual cortical response such as receptive field size, orientation selectivity, adaptation to repeated stimulation, response latency and visual acuity are virtually normal in dark-reared rats transplanted with polymer-encapsulated baby hamster kidney cells genetically engineered to release nerve growth factor.

Adaptation, Ocular↗
PubMed1989

Morphology of single, physiologically identified retinogeniculate Y-cell axons in the cat following damage to visual cortex at birth.

It has been reported previously that neurons in the dorsal lateral geniculate nucleus (LGN) of cats with neonatal damage to visual cortex (KVC cats) have receptive fields that are abnormally large and that the receptive fields of these neurons sometimes do not appear to conform to the normal retinotopic order in the LGN. A primary aim of this study was to determine if these physiological abnormalities are related to inappropriate patterns of retinogeniculate connections. We therefore have analyzed the terminal arbors of retinogeniculate axons in adult cats that had received a lesion of visual cortex (areas 17, 18, and 19) on the day of birth. Single retinogeniculate axons were characterized physiologically and injected intracellularly with horseradish peroxidase. Consistent with earlier reports that neonatal removal of visual cortex results in a retrograde loss of retinal X-cells, all of the retinogeniculate axons that we recorded were from Y-cells. While the visual responses of these Y-cell axons were normal, the morphology of their terminal arbors in the LGN was abnormal. Retinal Y-cell axons in KVC cats have terminal fields in the A laminae of the LGN that are as large or larger than those of normal Y-cells. However, since the LGN in KVC cats is severely degenerated, single Y-cell arbors occupy a proportional volume of the LGN that is 12 times greater than normal. Thus an early lesion of visual cortex produces a severe mismatch between retinogeniculate axon arbor size and target size. Also, despite the normal size of retinogeniculate axon arbors in KVC cats, the number and density of terminal boutons are greatly decreased. Thus our morphological results suggest that the unusually large receptive fields of LGN cells in KVC cats and the relative lack of retinotopic precision in the LGN are due, at least in part, to anomalies in the relative size and distribution of retinogeniculate axon arbors that develop after neonatal removal of visual cortex.

Animals↗
PubMed1987

Source of cholinergic input to ferret visual cortex.

The source of cholinergic input to ferret visual cortex was investigated with a combination of retrograde transport of horseradish peroxidase and choline acetyltransferase immunohistochemistry. Cholinergic projections to ferret visual cortex arise from basal forebrain cells in the septum, diagonal and nucleus basalis magnocellularis; the largest contribution comes from cells in the caudal part of the nucleus basalis magnocellularis. There is no discernible source in the brainstem.

Afferent Pathways↗
PubMed1988

Cerebral metabolism and patterned visual stimulation: a positron emission tomographic study of the human visual cortex.

We studied the impact of visual stimulation upon cerebral metabolism in normal young men using FDG-PET. Results obtained from subjects receiving patterned visual stimulation while performing an ocular fixation task were compared with results from ocular fixation alone. Visual stimulation in the macular region of either hemifield produced significant increases in metabolism of the contralateral posterior striate cortex. Visual stimulation induced highly significant asymmetries in metabolism of the prefrontal and inferior parietal cortices. Metabolic activation in extrastriate areas tended to be right-sided. These findings support the classic notion of retinotopic organization within the primary visual sensory cortex. They also indicate that the patterns of cerebral metabolism are not equivalent between the two cerebral hemispheres. This latter finding suggests that in humans the right cerebral hemisphere may be specialized for visual processing.

Adolescent↗
PubMed1984

Stimulus specificity of binocular cells in the cat's visual cortex: ocular dominance and the matching of left and right eyes.

Most cells in the striate cortex respond to visual stimulation through either eye. We have examined quantitatively the matching of response specificity for the two eyes. Our intention was to determine the degree to which this matching depends on ocular dominance. We used standard single cell recording techniques and studied responses to sinusoidal gratings of different spatial frequencies, orientations, and contrasts. For all tests, stimuli were randomly interleaved both with respect to the value of each parameter, and the eye which was stimulated. After estimating ocular dominance qualitatively and quantitatively, we measured: response modulation (to help identify whether a cell was simple or complex), orientation and spatial frequency tuning, and contrast response functions (to estimate contrast thresholds). Results show that: (1) Response modulation is well matched between the two eyes, but there is a slight tendency for the dominant eye to respond with less modulation. (2) Optimal orientation and spatial frequency and their respective tuning widths were similar for the two eyes. In general, tuning functions for the two eyes differed mainly in slope. However, in each case, there was a tendency for the dominant eye to have broader tuning widths. (3) In most cases, contrast response functions for the two eyes differed mainly in their slopes. Extrapolation to spontaneous levels suggests that estimated contrast thresholds are relatively independent of ocular dominance although, again, there ws a tendency for the dominant eye to exhibit slightly lower estimated thresholds. These findings demonstrate that response characteristics between the two eyes are generally well matched regardless of relative response strength. There are, however, small but clear differences between the two eyes for all parameters we measured which are related to and demonstrate that ocular dominance influences the degree of matching between the two eyes.

Animals↗
PubMed2004

Projections from primary visual cortex to cytochrome oxidase thin stripes and interstripes of macaque visual area 2.

It has been controversial whether the cytochrome oxidase (CO)-dense blobs in primate primary visual cortex (V1) and CO-dense thin stripes in visual area 2 (V2) are parts of a cortical color-processing stream that is segregated from other functional streams. One of the key pieces of evidence for the segregated color stream is the previous report of specific connections between blobs and thin stripes, which is parallel to the connections between interblobs and interstripes. To study the degree of the segregation between the proposed different streams, in the current study, anatomical tracers were injected into different V2 compartments with the functional guidance of optical imaging. The spatial relationship between each labeled cell and the CO blobs in V1 were analyzed quantitatively. After tracer injections in the color-preferring modules in CO thin stripes, equal amounts of labeled cells were found in the blobs and interblobs. However, the density of the labeled cells was more than twice as high in the blobs as that in the interblobs, and most of the clusters of labeled cells partially overlapped with the blobs. Tracer injections in the interstripes labeled cells predominantly in the interblobs. Our results suggest that both the blobs and interblobs project to the thin stripes and call into question the proposition that different CO compartments in V1 and V2 are connected in parallel to form highly segregated functional streams.

Animals↗
PubMed1995

Visual cortex activation in blind humans during sound discrimination.

We used a whole-scalp magnetometer with 122 planar gradiometers to study the activity of the visual cortex of five blind humans deprived of visual input since early infancy. Magnetic responses were recorded to pitch changes in a sound sequence when the subjects were either counting these changes or ignoring the stimuli. In two of the blind subjects, magnetic resonance images were also obtained, showing normal visual cortex macroanatomy. In these subjects, the magnetic responses to counted pitch changes were located at visual and temporal cortices whereas ignored pitch changes activated the temporal cortices almost exclusively. Also in two of the other three blind, the visual-cortex activation was detectable in the auditory counting task. Our results suggest that the visual cortex of blind humans can participate in auditory discrimination.

Acoustic Stimulation↗
PubMed1999

Dynamics of spatial summation in primary visual cortex of alert monkeys.

One of the fundamental tasks of the visual cortex is to integrate input from different parts of the retina, parsing an image into contours and surfaces, and then assembling these features into coherent representations of objects. To examine the role of the primary visual cortex in the integration of visual information, we measured the response properties of neurons under different stimulus conditions. Surprisingly, we found that even the most conventional measures of receptive field (RF) size were not fixed, but could vary depending on stimulus contrast and foreground-background relationships. On average, the length of the excitatory RF was 4-fold greater for a low-contrast stimulus than for a stimulus at high contrast. Embedding a high-contrast stimulus in a textured background tended to suppress neuronal responses and produced an enlargement in RF size similar to that observed by decreasing the contrast of an isolated stimulus. The results show that RF dimensions are regulated in a dynamic manner that depends both on local stimulus characteristics, such as contrast, and on global relationships between a stimulus and its surroundings.

Animals↗
PubMed2003

Organization of the visual cortex in human albinism.

In albinism there is an abnormal projection of part of the temporal retina to the visual cortex contralateral to the eye. This projection, together with the normally routed fibers from nasal retina, provides a cortical hemisphere with visual input from more than the normal hemifield of visual space. In many mammalian models of albinism, a possible sensory mismatch in the visual cortex is avoided either by reorganization of the thalamocortical connections to give the abnormal input an exclusive cortical representation, or by the abnormal input being substantially suppressed. In this study we examine, with fMRI, how the human visual cortex topographically maps its input in albinism. We find that the input from temporal retina is not substantially suppressed and forms a retinotopic mapping that is superimposed on the mapping of the nasal retina in striate and extrastriate areas. The abnormal routing of temporal fibers is not total, with the line of decussation shifting to between 6 and 14 degrees into temporal retina. Our results indicate that the abnormal input to visual cortex in human albinism does not undergo topographic reorganization between the thalamus and cortex. Furthermore, the abnormal input is not significantly suppressed in either striate or extrastriate areas. The topographic mapping that we report in human does not conform, therefore, to the commonly observed patterns in other mammals but takes the form of the "true albino" pattern that has been reported rarely in cat and in the only other individual primate studied.

Adult↗
PubMed1993

Immunocytochemical study of GABAA receptors in the cat visual cortex.

The laminar distribution and morphological structures associated with GABAA receptor immunoreactivity in the cat visual cortex were studied by using two different polyclonal antibodies directed either against the purified GABAA receptor protein (antibody "967") or against a specific domain of the beta 1-subunit of the GABAA receptor (antibody "Q"). Immunoblots of cat visual cortex tissue with these antibodies revealed that antibody "Q" recognizes only one subunit, namely the beta 1-subunit of the GABAA receptor, and that antibody "967" recognizes three subunits. Both antibodies produced very similar staining patterns, indicating that the beta 1-subunit may be an essential component of the GABAA receptor in the cat visual cortex. The typical staining pattern showed a clear membrane structure around neuronal somata. Using cell body shape criteria, immunopositive neurons included both pyramidal cells in cortical layers II, III, and V, and nonpyramidal cells in all cortical layers. Immunopositive neurons were uniformly distributed in layers II to VI, whereas the density of immunopositive cells in layer I was lower. Some immunopositive neurons were also found in the white matter underlying the visual cortex. In gray matter, immunopositive structures also included dendrites, especially the proximal dendrites, and axon initial segments of pyramidal neurons. The immunopositive processes usually ran vertically toward the pial surface. Some astrocytes were also immunostained. They were localized in layer I and in the white matter. The overall pattern of immunostaining was similar in areas 17, 18, and 19.

Amino Acid Sequence↗
PubMed1995

Topographical representations of mental images in primary visual cortex.

We report here the use of positron emission tomography (PET) to reveal that the primary visual cortex is activated when subjects close their eyes and visualize objects. The size of the image is systematically related to the location of maximal activity, which is as expected because the earliest visual areas are spatially organized. These results were only evident, however, when imagery conditions were compared to a non-imagery baseline in which the same auditory cues were presented (and hence the stimuli were controlled); when a resting baseline was used (and hence brain activation was uncontrolled), imagery activation was obscured because of activation in visual cortex during the baseline condition. These findings resolve a debate in the literature about whether imagery activates early visual cortex and indicate that visual mental imagery involves 'depictive' representations, not solely language-like descriptions. Moreover, the fact that stored visual information can affect processing in even the earliest visual areas suggests that knowledge can fundamentally bias what one sees.

Brain Mapping↗
PubMed2004

Perceptual learning of line orientation modifies the effects of transcranial magnetic stimulation of visual cortex.

Perceptual learning may be accompanied by physiological changes in early visual cortex. We used transcranial magnetic stimulation (TMS) to test the postulate that perceptual learning of a visual task initially performed at 60-65% accuracy strengthens visual processing in early visual cortex. Single pulse TMS was delivered to human occipital cortex at time delays of 70-154 ms after the onset of an odd-element, line orientation discrimination task. When TMS was delivered at a delay of 84 ms or later the accuracy of visual discrimination was transiently degraded in ten subjects. As visual performance in control trials without TMS improved with training, the absolute magnitude of TMS suppression of performance decreased in parallel. This result occurred both when TMS was delivered to broad areas of occipital cortex and when TMS was optimally delivered to early occipital cortex. No change in TMS suppression was observed when three new subjects were given feedback during an odd-element task that did not require substantial perceptual learning. Thus, perceptual learning improved visual performance and reduced TMS suppression of early visual cortex in parallel.

Adolescent↗
PubMedDate not supplied

Activation of metabotropic glutamate receptors has different effects in different layers of cat visual cortex.

Single neurons were recorded in cat primary visual cortex, and the effect of iontophoresis of the metabotropic glutamate agonist 1S,3R-aminocyclopentane-1,3-dicarboxylic acid (ACPD) was observed. In nearly all cases (41/43), ACPD reduced the visual response. In some cases ACPD also reduced spontaneous activity (24/43), and in other cases ACPD increased spontaneous activity (18/43). Increases were generally seen in infragranular layers (V and VI), and decreases in supragranular layers (II and III). The reduction in the visual response was also largest in supragranular layers. We conclude that activation of metabotropic glutamate receptors has both facilitatory and depressive effects in visual cortex, and the effect depends on the layer of the cell recorded.

Animals↗
PubMed1987

Retinotopic organization of human visual cortex mapped with positron-emission tomography.

The retinotopic organization of primary visual cortex was mapped in normal human volunteers. Positron-emission tomographic measurements of regional cerebral blood flow were employed to detect focal functional brain activation. Oxygen-15-labeled water, delivered by intravenous bolus, was used as the blood flow tracer to allow multiple stimulated-state (n = 5) and control-state (n = 3) measurements to be acquired for each of 7 subjects. Responses were identified by applying a maximum-detection algorithm to subtraction-format images of the stimulus-induced change in cerebral blood flow. Response locales were described using a standardized system of stereotactic coordinates. Changes in stimulus location (macular, perimacular, peripheral, upper-field, lower-field) caused systematic, highly significant changes in response locale within visual cortex. Discrete extrastriate visual responses were also observed.

Adult↗
PubMed1996

Baseline, visual deprivation and visual stimulation 99TCm-HMPAO-related changes in visual cortex can be detected with a single-head SPET system.

To determine the sensitivity of 99TCm-hexamethylpropylene amine oxime (99TCm-HMPAO) and a single-head SPET (single photon emission tomography) system in the detection of perfusion changes in the visual cortex due to different visual conditions, six normal healthy volunteers were studied under conditions of visual deprivation (blindfolded), visual stimulation (stroboscopic light) and baseline (dim light and eyes open). Visual cortex/whole-brain activity ratios, and the percentage of activity change between the different visual conditions were calculated after three-dimensional realignment of the images. The activity in the visual cortex was higher during visual stimulation than during the visual deprivation (P = 0.002, 17.6 +/- 8.6% increase) and baseline conditions (P = 0.009, 8.8 +/- 5.6% increase). Furthermore, the activity in the visual cortex was lower during the visual deprivation than in the baseline condition (P = 0.001, 8.1 +/- 2.9% decrease). 99TCm-HMPAO SPET, even with a single-head system, is capable of detecting changes in rCBF in the striate cortex, not only between conditions of visual stimulation and deprivation, but also between these two conditions and the baseline state.

Adult↗
PubMed2003

Postnatal development of GFAP in mouse visual cortex is not affected by light deprivation.

Mammalian visual cortex is immature at birth and develops gradually during defined postnatal temporal windows. In the present work, we studied the maturation of astrocytes in developing mouse visual cortex (VC). The cellular distribution and the level of glial fibrillary acidic protein (GFAP) were analyzed by immunohistochemistry and Western blotting. Experiments were performed at different postnatal ages: postnatal day 12 (P12), before eye opening; P24, corresponding roughly to the peak of the critical period for monocular deprivation, and P60, after the end of the critical period. At P12, GFAP immunoreactivity (IR) was distributed throughout all cortical layers. At P24, there was a prominent localization of GFAP IR in layers I, II, and VI, while cortical layers III, IV, and V contained no longer GFAP IR cells. No differences were found in GFAP IR between P24 and P60. Western blot analysis revealed a reduction of GFAP expression in the VC at P24 with respect to P12 and no significant difference between P60 and P24. These results show that GFAP expression is modulated during early postnatal development. To know whether visual experience influences the maturation pattern of GFAP expression, mice were dark-reared from P12 to P24. Dark rearing did not change the distribution and the expression of GFAP. Our results indicate that maturation of GFAP expression occurs early in postnatal development in mouse VC. In addition, we showed that GFAP development is not affected by visual deprivation.

Aging↗
PubMed2005

Light-induced Fos expression in phosphate-activated glutaminase- and neurofilament protein-immunoreactive neurons in cat primary visual cortex.

Previous double-stainings in the cat visual cortex [E. Van der Gucht, S. Clerens, K. Cromphout, F. Vandesande, L. Arckens, Differential expression of c-fos in subtypes of GABAergic cells following sensory stimulation in the cat primary visual cortex, Eur. J. Neurosci. 16 (2002) 1620-1626] showed that a minority of Fos-immunoreactive nuclei was located in distinct subclasses of inhibitory neurons following sensory stimulation. This report describes double-stainings between Fos and phosphate-activated glutaminase (PAG) or Fos and neurofilament protein (SMI-32) revealing that, following a short-term visual experience, Fos is also expressed in neurochemically distinct subpopulations of non-GABAergic, pyramidal neurons in supra- and infragranular layers of cat area 17.

Animals↗
PubMed1991

Fibre divergence in the distal optic radiation: possible basis of functional plasticity in adult primate visual cortex.

The precision of retinotopy in primate visual cortex is commonly thought to result from highly ordered arrangement of fibres in the visual pathways. However, rigid point-to-point representation is hardly compatible with findings of a substantial reorganization of visual cortical maps after peripheral and central lesions. Such observations could be accounted for by divergence in the optic radiation. To explore the hypothesis of fibre divergence, we made small knife cuts in the distal optic radiation of macaca fascicularis. After subsequent axonal tracing by injecting WGA-HRP into lateral geniculate nucleus, we studied the course of distal fibres in white matter. The amount of divergence was assessed by measuring, relative to the prevailing fibre course, length and orientation of labelled fibres between lesion and entry into cortex. Lesion sizes between 1 mm to 3 mm did not result in any detectable diminution of terminal labelling in layer IVC of striate cortex. Individual labelled fibres were found to diverge symmetrically from both sides into the gap distal to the lesion. Divergence starts at a distance of about 3 mm before cortex. At the white matter boundary, less than 10% of all fibres still retain the original direction, with the remaining fibres taking any other orientation without preference. We estimate that this corresponds to a divergence of visual afferents encompassing about 6-10 mm of cortical distance, if intracortical arborization of terminal fibres is taken into account. Possible consequences for functional plasticity in the adult primate visual cortex are discussed.

Animals↗