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At least 289 records · Page 16Linked to original sources

PubMed1991

Flashed pattern-induced activity in the visual system: I. The short latency evoked response recorded from the cat visual cortex.

Previous methods for estimating visual acuity have used the visual evoked response conventionally the late visual evoked response components or the steady-state potential. The present experiments were undertaken to evaluate the possible use of short latency flashed pattern evoked responses in estimating pattern dependent activity in the cat visual system. Recordings were made from the skull bone and the dura above the primary visual cortex and intracortically. The visual evoked responses to patterned (checks) and non-patterned light flashes of high intensity and short duration were recorded. The visual evoked response activity recorded from the cortical surface had an onset latency of 14-15 ms. The initial positive-negative potential sequences of the responses were similar for patterned and non-patterned stimuli, however a difference was recorded from 35-40 ms after stimulus. The smallest check size which separated a pattern from a non-pattern VER was in the order of 10 min of arc. The results indicate that the short-latency cortical VER may be used to estimate visual resolution.

Animals↗

PubMed1991

Lithium reduces ocular dominance plasticity in kitten visual cortex.

Activity-dependent processes within the visual pathway play a crucial role in the expression of ocular dominance plasticity in immature visual cortex. The necessity of non-retinal, modulatory afferents to the regulation of ocular dominance plasticity has been recognized. Among a few chemically defined signaling systems, the noradrenaline-activated beta-adrenoreceptors seem to have a prime role in this matter. The involvement of acetylcholine afferents was also proven. We looked for plausible molecular mechanisms which integrate the contribution of the two neuromodulator systems to ocular dominance plasticity. At the first step, based on the rich literature on psychotropic action of lithium and the recent advancement in understanding of its molecular mechanisms, we physiologically studied visual cortex of kittens which had been repeatedly injected with the lithium solution intraperitoneally or the cortex directly infused with it. We found (1) that ocular dominance plasticity was significantly reduced in lithium-injected kittens, (2) that the decrease was directly correlated with plasma concentrations of lithium (i.e. the higher the lithium concentration, the lower the plasticity), and (3) that the comparable decrease in the plasticity was obtained from kitten visual cortex which had been directly infused with the lithium solution. The present results suggest that lithium-sensitive processes, through most likely reduced production of second messengers, underlie the regulation of ocular dominance plasticity.

Animals↗

PubMed1975

[Reflection of temporal parameters of an optic stimulus in neuronal responses of the senso-motor and visual cortex in cats].

Neuronal extracellular discharges in visual (area 17) and sensory-motor (area 4 and 6) cortical fields to optical stimuli with a duration up to 1000 ms were examined in the chloralozed cats (70 mg/kg). A comparative analysis of neuronal discharge types and of functional shift intervals revealed: 1) an amount of neurons with on--off discharges in the visual cortex is 25% and in the sensory-motor cortex--100%; 2) the functional shift intervals coincide with the on--off discharge time interval for the same neurons; 3) alongside with the common time interval there are specific ranges for each zone (0--200 ms for the visual cortex; 500 ms and more for the sensory-motor cortex); 1) the afterdischarge latency of a neuron is equal to the functional shift interval value of the same neuron. These data are considered as a reflection of the optical signal time parameters by the sensory-motor cortical neurons. Such peculiarities of the sensory-motor area might be important for the time organization of the cortical movement program.

Animals↗

PubMed1998

Axotomy-induced neuronal death and reactive astrogliosis in the lateral geniculate nucleus following a lesion of the visual cortex in the rat.

Following a unilateral lesion of the visual cortex (cortical areas 17, 18, and 18a) in adult rats, neurons in the ipsilateral dorsal lateral geniculate nucleus (LGN) are axotomized, which leads to their atrophy and death. The time course of this neuronal degeneration was studied quantitatively, and the astroglial response was examined with glial fibrillary acidic protein immunohistochemistry. More than 95% of the neurons in the ipsilateral LGN survive during the first 3 days following a lesion of the visual cortex. However, in the next 4 days, massive neuronal death ensues, reducing the number of surviving neurons to approximately 33% of normal by the end of the first postoperative week. Between 2 weeks and 24 weeks postoperatively, the number of neurons present in the LGN declines very gradually from 34% to 17% of normal. Three days after a lesion of the visual cortex, the mean cross-sectional areas of ipsilateral LGN neurons are 13% smaller than normal (87%). By 1 week after the operation, surviving LGN neurons have atrophied to 66% of their normal area. Subsequently, the size of surviving neurons declines slowly to approximately 50% of normal at 24 weeks after the cortical lesion. Astrocytes in the ipsilateral LGN also react to cortical damage. At 1 day after a lesion of the visual cortex, glial fibrillary acidic protein immunoreactivity in the LGN is almost undetectable, but a distinct increase in immunoreactivity is seen at 3 days. Immunoreactivity peaks between 1 week and 2 weeks postoperatively and, thereafter, remains intense for at least 24 weeks. Thus, following a lesion of the visual cortex, the somata of neurons in the LGN remain essentially normal morphologically for about 3 days before the onset of rapid atrophy and death. Moreover, most of the neural cell death that occurs in the LGN after axotomy takes place in the last half of the first postoperative week.

Animals↗

PubMed1991

Regressive changes among corticocortical neurons projecting from the lateral suprasylvian cortex to area 18 of the kitten's visual cortex.

The postnatal development of corticocortical neurons projecting from the medial bank of the lateral suprasylvian cortex to area 18 of the kitten's visual cortex was examined using retrograde fluorescent tracers. Area 18 was injected in young kittens aged nine days or less and in older kittens aged 30 days or more. Many of the injected kittens were perfused with fixative four to five days later, but some of the youngest were killed after longer survival periods of 35-50 days (long-survival animals). Labelled neurons in the medial bank of the lateral suprasylvian cortex were densely distributed in both superficial layers (II and III) and deep layers (V and VI) in the kittens injected less than nine days postnatal, irrespective of whether survival was short or long, but they were found almost exclusively in layers V and VI in the old, short-survival animals. Only in the group of old kittens did we find a clear topographical arrangement of projections in the rostrocaudal direction and a correlation between the rostrocaudal lengths of the injection sites and labelled areas. In the other two groups, for a similarly sized injection site, the labelled areas were much longer rostrocaudally than in the old, short-survival kittens, and occupied roughly the posterior two-thirds of the medial bank of the lateral suprasylvian cortex, irrespective of the positions of the injections. In the frontal plane, topography was unclear in all groups. These findings demonstrate that there is considerable postnatal refinement of the projection from the medial bank of the lateral suprasylvian cortex to area 18. This involves a loss of connections originating from superficial layers and a decrease of convergence with the appearance of topography. Our results from long-survival kittens suggest that most of the early exuberant population of corticocortical neurons projecting from the medial bank of the lateral suprasylvian cortex to area 18 survive beyond the first postnatal month but undergo axonal elimination during this period.

Aging↗

PubMed1989

Responses of lateral geniculate neurons that survive long-term visual cortex damage in kittens and adult cats.

Damage to visual cortex (areas 17-19) in kittens or adult cats produces severe retrograde degeneration of neurons in the dorsal lateral geniculate nucleus (LGN). However, some neurons survive in otherwise degenerated portions of the LGN after a visual cortex lesion at any age. Previous studies have shown that there are well-defined differences in potential retinal inputs, soma size, synaptic connections, outputs, and physiological properties of output targets of the surviving LGN cells in cats that received visual cortex damage at different ages. The present experiment investigated the relationships between these differences and the responses of surviving LGN neurons to visual stimulation. Recordings were made from surviving neurons in the degenerated A- and C-layers of the LGN in cats that had received a visual cortex lesion on the day of birth, at 8 weeks of age, or as adults (survival was 11.5-36 months). Normal adult cats were studied for comparison. The visual receptive field was mapped, and tests were carried out to classify each cell as X, Y, or W. In addition, quantitative methods were used to assess response amplitude, strength of receptive-field surround inhibition, spatial-frequency tuning to drifting or counterphased sine-wave gratings, and response to nondominant-eye stimulation for each cell. We found that surviving cells in all LGN layers respond to light, have normal receptive-field organization, and have normal eye dominance following a lesion at any age tested. In addition, gross retinotopic organization of the LGN is normal. However, 2 main abnormalities were observed following a lesion at all 3 ages. First, there is a reduction in the percentage of X cells in the A layers, from 62% in normal LGNs to about 15% in degenerated LGNs. Second, many surviving cells in both the A- and C-layers have abnormally large receptive-field centers. Other differences that were observed between normal A-layer cells and surviving A-layer cells could be attributed to the loss of X cells. These results indicate that cells within a structure that shows severe retrograde degeneration after brain damage can maintain relatively normal function and can take part in potentially important residual neural pathways. Previous studies indicate that these residual pathways can show both anatomical and physiological compensation for the brain damage, and the present findings bear on the consequences and mechanisms of this compensation.

Animals↗

PubMed2001

Functional retinotopy of monkey visual cortex.

The operations of primary visual cortex generate continuous representations of orientation, ocular dominance, and retinotopy that, to fit in two dimensions, organize at separate but overlapping scales (e.g., 20-500 microm, 200 microm to 5 mm, and 2-33 mm). Where their scales overlap, these organizations interact; iso-orientation contours cross ocular dominance columns at right angles, and ocular dominance columns distort retinotopy near the V1/V2 border. To explore these interactions, we developed an optical technique for visualizing retinotopy in vivo that allows us to analyze it in relation to ocular dominance and orientation patterns. Our results show local retinotopic distortions in every region of macaque V1 that we examine, including regions far from the V1/V2 border. They also show a consistent relation between local axes of distortion and ocular dominance slabs, which they intersect at angles of approximately 90 degrees. A further correlation is provided by retinotopic maps from New World primates that show less distortion (9 vs 60%) in two species characterized by an absence of pronounced ocular dominance columns. Retinotopic maps from these New World primates also revealed an unexpected tilt of the vertical midline representation that diverged from the V1/V2 border by an angle of approximately 20 degrees. Overall, these results suggest a general tendency for slab-based organizations to distort retinotopy by representing the same part of space more than once in adjacent slabs.

Animals↗

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↗

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↗

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↗