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At least 1,225 records · Page 68Linked to original sources
PubMed2003

Parallel colour-opponent pathways to primary visual cortex.

The trichromatic primate retina parses the colour content of a visual scene into 'red/green' and 'blue/yellow' representations. Cortical circuits must combine the information encoded in these colour-opponent signals to reconstruct the full range of perceived colours. Red/green and blue/yellow inputs are relayed by the lateral geniculate nucleus (LGN) of thalamus to primary visual cortex (V1), so understanding how cortical circuits transform these signals requires understanding how LGN inputs to V1 are organized. Here we report direct recordings from LGN afferent axons in muscimol-inactivated V1. We found that blue/yellow afferents terminated exclusively in superficial cortical layers 3B and 4A, whereas red/green afferents were encountered only in deeper cortex, in lower layer 4C. We also describe a distinct cortical target for 'blue-OFF' cells, whose afferents terminated in layer 4A and seemed patchy in organization. The more common 'blue-ON' afferents were found in 4A as well as lower layer 2/3. Chromatic information is thus conveyed to V1 by parallel, anatomically segregated colour-opponent systems, to be combined at a later stage of the colour circuit.

Animals↗
PubMed1972

Neuronal correlates of eye movements in the visual cortex of the cat.

About 10 percent of the cells in the visual cortex of awake cats do not respond to stationary parallel stripes in any orientation or to stripes moving across the visual field in any direction at a moderate speed (up to 132 degrees per second), but these cells are either excited or inhibited during saccadic eye movements when the animal faces a patterned visual environment. Of nineteen such cells tested in total darkness, seven discharged in association with eye movements. For saccade-related discharges, the latency during retinal stimulation is typically shorter than the latencey in total darkness.

Action Potentials↗
PubMed1997

Immunocytochemical localization of calcium-binding protein calretinin containing neurons in cat visual cortex.

The distribution and morphology of neurons containing calretinin in area 17 of the cat visual cortex were studied. The calcium-binding protein calretinin was localized by antibody immunocytochemistry. Most of the calretinin-labeled neurons were located in layers I, II, and III. There were few calretinin-labeled cells in the other layers. The labeled neurons varied in morphology. The majority of the labeled neurons had small round or oval somas with long processes traveling perpendicular to the pial surface. Many small multipolar neurons were also labeled by this antibody. These results indicate that the calcium-binding protein calretinin is contained both in specific layers and selective cell types in the cat primary visual cortex.

Animals↗
PubMed2006

Limited plasticity of difference neurons in the visual cortex and hippocampus in rabbits during the oddball (random substitutions) test.

The activity of 41 visual cortex neurons and 20 hippocampal field CA1 neurons was studied in rabbits during application of the oddball stimulation paradigm using color stimuli of different intensities. Among these cells, about one third were plastic cells (34% of cortical cells and 37% of hippocampal cells). These neurons showed significant increases in late responses, at times 200-500 and 200-1000 msec for visual cortex neurons and 300-550 msec for hippocampal neurons, to rare deviant stimuli of lesser intensity as compared with responses to the frequent standard stimuli of greater intensity. The initial peak of the response (40-120 msec), the "difference discharge," remained stable in responses to deviant and standard stimuli throughout the experiment. It is suggested that the strengthening of the late components of neuron responses to rare deviant stimuli (limited plasticity) reflects inclusion of the mechanisms of the orientational reflex.

Animals↗
PubMed1991

Thalamic projections to the lateral suprasylvian visual area in cats with neonatal or adult visual cortex damage.

Previous transneuronal anterograde tracing studies have shown that the retino-thalamic pathway to the posteromedial lateral suprasylvian (PMLS) visual area of cortex is heavier than normal in adult cats that received neonatal damage to visual cortical areas 17, 18, and 19. In contrast, the strength of this projection does not appear to differ from that in normal animals in cats that experienced visual cortex damage as adults. In the present study, we used retrograde tracing methods to identify the thalamic cells that project to the PMLS cortex in adult cats that had received a lesion of visual cortex during infancy or adulthood. In five kittens, a unilateral visual cortex lesion was made on the day of birth, and horseradish peroxidase (HRP) was injected into the PMLS cortex of both hemispheres when the animals were 10.5 to 13 months old. For comparison, HRP was injected bilaterally into the PMLS cortex of three cats 6.5 to 13.5 months after they received a similar unilateral visual cortex lesion as adults. In cats with a neonatal lesion, retrograde labeling was found in the large neurons that survive in the otherwise degenerated layers A and A1 of the lateral geniculate nucleus (LGN) ipsilateral to the lesion. Retrograde labeling of A-layer neurons was not seen in the undamaged hemisphere of these animals or in either hemisphere of animals that had received a lesion as adults. As in normal adult cats, retrograde labeling also was present in the C layers of the LGN, the medial interlaminar nucleus, the posterior nucleus of Rioch, the lateral posterior nucleus, and the pulvinar nucleus ipsilateral to a neonatal or adult lesion. Quantitative estimates indicate that the number of labeled cells is much larger than normal in the C layers of the LGN ipsilateral to a neonatal visual cortex lesion. Thus the results indicate that the heavier than normal projection from the thalamus to PMLS cortex that exists in adult cats after neonatal visual cortex damage arises, at least in part, from surviving LGN neurons in the A and C layers of the LGN. Although several thalamic nuclei, as well as the C layers of the LGN, continue to project to PMLS cortex after an adult visual cortex lesion, these projections appear not to be affected significantly by the lesion.

Aging↗
PubMed2001

Rate coding versus temporal order coding: what the retinal ganglion cells tell the visual cortex.

It is often supposed that the messages sent to the visual cortex by the retinal ganglion cells are encoded by the mean firing rates observed on spike trains generated with a Poisson process. Using an information transmission approach, we evaluate the performances of two such codes, one based on the spike count and the other on the mean interspike interval, and compare the results with a rank order code, where the first ganglion cells to emit a spike are given a maximal weight. Our results show that the rate codes are far from optimal for fast information transmission and that the temporal structure of the spike train can be efficiently used to maximize the information transfer rate under conditions where each cell needs to fire only one spike.

Animals↗
PubMed2002

Plasticity of the visual cortex after injury: what's different about the young brain?

The repercussions of localized injury of the cerebral cortex in young brains differ from the repercussions triggered by equivalent damage of the mature brain. In the young brain, some distant neurons are more vulnerable to the lesion, whereas others survive and expand their projections to bypass damaged and degenerated structures. The net result is sparing of neural processing and behaviors. This article summarizes both the modifications in visual pathways resulting from visual cortex lesions sustained early in life and the neural and behavioral processes that are spared or permanently impaired. Experiments using reversible deactivation show that at least two highly localizable functions of normal cerebral cortex are remapped across the cortical surface as a result of an early lesion of the primary visual cortex. Moreover, the redistributions have spread the essential neural operations underlying orienting behavior from the visual parietal cortex to a normally functionally distinct type of cortex in the visual temporal system, and in the opposite direction for complex-pattern recognition. Similar functional reorganizations may underlie sparing of neural processes and behavior following early lesions in other cerebral systems, and these other systems may respond well to emerging therapeutic strategies designed to enhance the sparing of functions.

Aging↗
PubMed1978

[Dynamics of rabbit visual cortex neuron reaction to presentation of repetitive photic stimuli].

Responses of visual cortex neurons to repeated light flashes with frequency of 1 stimulus per 2.5 were investigated in rabbits. Two forms of response dynamics (according to the total number of spikes in the response) were found: "fast" and "slow". 5--15 stimuli were required for the stabilization of the responses of the first form and 50--100 stimuli for that of the second form. About 50% of all the neurons showed stable responses. Partial habituation of responses was revealed in 55--59% of the neurons, sensitizations of discharge in 25% and hump-shared type of the response in 17--20% of neurons. "Slow" dynamic modifications of the responses in most neurons were associated with modifications in the duration of the inhibitory phases in the responses.

Animals↗
PubMed1994

Synaptic output of physiologically identified spiny stellate neurons in cat visual cortex.

Spiny stellate neurons of area 17 of the cat's visual cortex were physiologically characterised and injected intracellularly with horseradish peroxidase. Six neurons from sublamina 4A were selected. Five had the S-type of simple receptive fields; one had a complex receptive field. Their axons formed boutons mainly in layers 3 and 4. An electron microscopic examination of 45 boutons showed that each bouton formed one asymmetric synapse on average. Spines were the most frequent synaptic target (74%); dendritic shafts formed the remainder (26%). On the basis of ultrastructural characteristics, 8% of the target dendrites were characterised as originating from smooth gamma-aminobutyrate-ergic (GABAergic) neurons. Thus the major output of spiny stellate neurons is to other spiny neurons, probably pyramidal neurons in layer 3 and spiny stellates in layer 4.

Animals↗
PubMed1983

A functional model of the wiring of the simple cells of visual cortex.

A computer model of the simple cells in the mammalian visual cortex was constructed. The model cells received inputs from a great number of isopolar centre/surround cells assumed to be located in the lateral geniculate nucleus (LGN). The distribution of input to the model simple cells was either inhibitory/excitatory or inhibitory/excitatory/inhibitory. Such arrangements produced receptive fields containing four or five consecutively antagonistic subfields. Responses produced by the model cells to different types of stimuli (periodical as well as nonperiodical) were obtained and compared to responses of living cells reported from various laboratories under comparable stimulus conditions. In all the situations tested, the responses of the model cells corresponded qualitatively very well to those of living cells. It was seen that the same wiring mechanism was able to account for orientation selectivity, spatial frequency filtering, various phase relationships between stimulus and response, subfield orientational selectivity, and slight end-inhibition. Furthermore, the receptive fields of the model simple cells closely resemble Gabor functions.

Action Potentials↗
PubMed1979

[Identification of nerve cells in the visual cortex of the rat using Nissl and Golgi-Kopsch methods].

The neurons of the visual cortex of the albino rat were studied using both the Nissl- and Golgi-Kopsch methods. In Nissl preparations we can distinguish between a group of neurons rich in cytoplasm, a group of neurons poor in cytoplasm and an intermediate group. In the Golgi preparations the neurons can be subdivided according to the shape of their cell bodies, dendrites and axons. Spiny cells with long axonal main trunks are pyramidal cells, multiangular cells and stellate cells of layer IV. Cells with spineless dendrites and short axonal arborization are basket cells, neuroglioform cells and small double bouquet cells. Due to its spines and the short axonal arborization, the coarse fusiform cell (Martinotti cell) is an intermediate type. We assume cells having long axons and dendritic spines are category I neurons and cells having short axons and no or a few spines are category II neurons (according to SZENTAGOTHAI 1973). On the basis of homological criterions and taxonomically relevant features references for identifying the cell group rich in cytoplasm and category I neurons, on the one hand, and the cell group poor in cytoplasm and category II neurons, on the other hand, were found. The group of cells rich in cytoplasm is related to pyramidal cells, multiangular cells and stellate cells of lamina IV. The group of cells poor in cytoplasm is discussed as corresponding to cells of lamina I, round or oval forms as basket cells and neuroglioform cells, fusiform cells as double bouquet cells. The intermediate cell form in the Nissl preparations is according to the Martinotti cell in Golgi material. These findings allow quantitative studies about particular cell populations and can, completed with electron microscopical date, instruct computer models to simulate the complicate neuronal network of the visual cortex.

Animals↗
PubMed1979

[Structure and correlation of "fast" and "slow" background impulse activity of visual cortex neurons].

Background and optically modified impulse activity of neurons in visual cortex of unanaesthetized rabbits was analyzed. By means of joint interval histograms it was shown that neurons can be distinguished by the ratio of burts (intervals to 15-40 ms) and extraburst activity and by the shape of transition from one from of activity to another. The extraburst activity comprises 63% of impulses and its ratio to bursts of 2 or 3 and more impulses was 27:3:1. Burts impulse distribution showed a relative stability of timing pattern within bursts and small number of burst impulses (2.4 on the average). Bursts of 3 and more impulses (3.6 on the average) are not rhythmical and 79% of them contained long intervals (18.6 +/- 2.4 ms) before the shortest one (7.9 +/- 0.9 ms). Optical stimulation resulted in bursts containing core impulses, shorter intervals and beginning with the shortest interval in most neurons. This may testify to the increase of the EPSP steepness and amplitude. 20% of cortical neurons showed background bursts containing more impulses and shorter intervals in comparison with evoked bursts.

Animals↗
PubMed2002

Absence of long-term depression in the visual cortex of glutamic Acid decarboxylase-65 knock-out mice.

Long-term depression (LTD) is widely considered a mechanism for experience-induced synaptic weakening in the brain. Recent in vivo studies on glutamic acid decarboxylase [GAD 65 (-/-)] knock-out mice indicates that GABAergic synaptic inhibition is also required for the normal weakening of deprived inputs in the visual cortex. To better understand how GABAergic inhibition might control plasticity, we assessed the status of synaptic inhibition and LTD in visual cortical slices of GAD 65 knock-out mice. We found the following: (1) the efficacy of GABAergic synapses during repetitive activation is reduced in GAD 65 (-/-) mice; (2) the induction of LTD is impaired in the visual cortex of GAD 65 (-/-) mice; and (3) chronic, but not acute, treatment with the benzodiazepine agonist diazepam restores LTD in GAD 65 (-/-) mice. These results suggest that a certain inhibitory tone is required for the induction of LTD in visual cortex. We propose that the lack of visual cortical LTD in GAD 65 (-/-) may account for the lack of experience-dependent plasticity in these mice.

Animals↗
PubMed1994

Interhippocampal transfer of place navigation monocularly acquired by rats during unilateral functional ablation of the dorsal hippocampus and visual cortex with lidocaine.

To study the neural mechanisms of interhippocampal transfer of lateralized place navigation engrams in rats, lidocaine was injected via chronically implanted cannulae to reversibly inactivate the hippocampal formation and the visual cortex on one side. The eye opposite the blocked side was occluded. Under these conditions, rats learned the location of an invisible platform in a water maze [mean escape latencies per four-trial block (t) = 5-6 s at the performance asymptote]. Monocular intact brain retrieval with the trained eye (t = 7) was better than with the untrained eye (t = 13). However, analysis of each retrieval trial indicated untrained eye performance was only poor on the first trial (t = 30). To test whether trans-commissural read-out alone or write-in (i.e. interhippocampal transfer) of the lateralized engram explains the above results, rats acquired a new platform location (t = 5). Two groups were then given a 30-s "free swim" (the platform was removed) with intact brain and either the trained or untrained eye occluded. A third group did not have this "transfer" trial. Retrieval was tested with the trained hippocampus and visual cortex blocked. With the trained eye occluded, retrieval in the rats that had the transfer trial (t = 11) was better than in those that did not (t = 25), but slightly worse than in rats tested with the untrained eye, hippocampus and visual cortex blocked (t = 7). Additionally, retrieval was similar, independent of whether the trained (t = 12) or untrained (t = 11) eye was open on the transfer swim. The 30-s swim alone did not induce comparable savings. We conclude that interhippocampal transfer of lateralized place learning is easily induced, is equal if the transfer is facultative or imperative, and involves both trans-commissural read-out and write-in processes.

Animals↗
PubMed1982

The termination of geniculocortical fibres in area 17 of the visual cortex in the macaque monkey.

The termination of geniculocortical fibres within the different subdivisions of lamina IV in area 17 of the visual cortex of the monkey has been studied quantitatively with the electron microscope. In lamina IVC alpha the axon terminals of fibres coming from the magnocellular layers of the lateral geniculate nucleus (LGN) make significantly more synapses per bouton than those of fibres arising from the parvocellular layers and terminating in laminae IVA and IVC beta. In all parts of area 17 examined there was a clear difference in the relative proportions of multisynaptic geniculocortical boutons between the alpha and beta divisions of lamina IVC. Calculations have shown that a single cell in the magnocellular laminae of the LGN may make about 6 times as many synaptic contacts within lamina IV of the visual cortex than one in the parvocellular laminae. It has also been estimated that there are at least 500 million geniculocortical boutons, or 1200 million synapses, in lamina IVC alpha and 100 million boutons, 1200 million synapses, in lamina IVC beta for one hemisphere, giving an approximate total number of 1500 million boutons and 2400 million synapses.

Animals↗
PubMed2000

Androgens reduce cell death in the developing rat visual cortex.

We have previously shown that males have more neurons than females in the primary visual cortex, and neonatal androgens play an important role in this difference. Also, we have found that females experience more cell death during development in this region than in males. Therefore, we hypothesized that the neonatal hormone environment directly influences the amount of cell death. In the present experiment, female rats were implanted with dihydrotestosterone (DHT) or estradiol at postnatal day 1. These animals, along with control males and females, were sacrificed on postnatal days 6, 11 and 25. Using unbiased stereology to quantify neuronal and pyknotic cell density, we observed that females implanted with DHT had a similar pattern and proportion of cells dying as control males. Additionally, developmental cell death in females implanted with estradiol was not significantly different than control females. Thus, neonatal androgens have an inhibitory effect on developmental cell death in the rat primary visual cortex.

Animals↗
PubMed2000

Developmental changes in the expression of NMDA receptor subunits (NR1, NR2A, NR2B) in the cat visual cortex and the effects of dark rearing.

The present study used Western blots to determine changes in the level of expression of the three major NMDA receptor subunits, NR1, NR2A, and NR2B, in relation to the 'critical period' in cat visual cortex. NR2A rose dramatically (10-fold) from very low levels at 1 week to a peak at 5 weeks and gradually declined into adulthood (twofold). NR2B showed a similar time course to NR2A, but the rise from 1 to 5 weeks was of lesser magnitude (twofold). NR1 was expressed at comparable levels at 1, 5, 10 weeks and declined markedly (fivefold) in older animals. No significant effects of dark rearing on the levels of NR2B and NR1 were found. However, NR2A expression was significantly elevated in normal compared to dark reared visual cortex (twofold) at 5 weeks and significantly elevated in dark reared compared to normal visual cortex at 20 weeks (twofold). The close agreement between NR2A expression and both the time course of the critical period and the effects of dark rearing on that time course further indicates a role of this subunit in visual cortical critical period plasticity.

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