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[Characteristics of the stability of functional interhemispheric asymmetry in the cat visual cortex].

A study of EP topography in the cat visual cortex has shown that initial functional interhemispheric asymmetry may be reduced and replaced by symmetry through long and frequent binocular stimulation. Section of the callosal body produced an inversion of one hemisphere dominance. In the callosotomized animals binocular stimulation enhanced the asymmetry. It is more stable in the cat visual cortex than in rats.

Animals↗
PubMed1989

The development of N-methyl-D-aspartate receptors in cat visual cortex.

During a critical period of early postnatal development, the visual cortex of kittens is susceptible to experience-dependent modifications of neuronal response properties. Recently, the activation of N-methyl-D-aspartate (NMDA) receptors has been identified as an indispensable prerequisite for the induction of such modifications. We therefore investigated developmental changes in the density and distribution of NMDA receptors and questioned whether these showed a relation to the time course of the critical period. We determined the proportion of [3H]glutamate binding sites that were displaced by the NMDA receptor antagonist 2-amino-5-phosphonovalerate (APV) on 10-microns-thick cryostat sections of the primary visual cortex. The overall density of APV-sensitive [3H]glutamate binding sites increased dramatically between the second and the fourth week and stayed at this level throughout the critical period. Towards the end of the critical period, these binding sites decreased and finally reached adult values that were slightly above those of 2-week-old kittens. APV-sensitive binding sites were present in all cortical layers of the age groups investigated. While the general pattern of developmental changes was similar in all layers, slight differences existed in the time course. These observations are compatible with the notion that NMDA receptor activation is required for the expression of use-dependent change of response properties in the kitten visual cortex. Furthermore, they suggest as a possible reason for the decline of malleability towards the end of the critical period the reduction of NMDA receptors.

2-Amino-5-phosphonovalerate↗
PubMed2004

Posterior neocortical (visual cortex) lesions in the rat impair matching-to-place navigation in a swimming pool: a reevaluation of cortical contributions to spatial behavior using a new assessment of spatial versus non-spatial behavior.

In the face of contradictory findings on the role of visual cortex contributions to spatial behavior, the present study evaluated the ability of rats with primary visual cortex (Area 17) lesions to learn spatial problems in a swimming pool. Because the solution to any spatial learning problem consists of acquiring at least two primary elements of a task, task procedures and spatial learning, the study, in addition to assessing spatial ability on a place task, used two training/testing methods to identify the nature of the spatial impairment associated with visual cortex lesions. Non-spatial training consisted of learning to find a platform in the dark and spatial training consisted of a series of matching-to-place problems. The results confirmed that although rats with visual cortex lesions were impaired on place learning, the deficit was partially ameliorated by non-spatial training given following the lesion, and completely ameliorated by non-spatial training given before the lesion. Nevertheless, all visual cortex groups failed to show a quadrant preference on a probe trial and displayed a profound impairment in matching-to-place learning. This definitive demonstration that appropriate testing methods can reveal a failure in spatial behavior following visual cortex lesions is consistent with the idea that primary visual cortex is required in spatial navigation.

Analysis of Variance↗
PubMed2005

Functional impact of primary visual cortex deactivation on subcortical target structures in the thalamus and midbrain.

The functional relationships between the primary visual cortex and its major subcortical target structures have long been a subject of interest. We studied these relationships by using localized cooling deactivation to silence portions of primary visual cortex and measuring 2-deoxyglucose (2DG) uptake to assess neural activity in subcortical and midbrain targets. We focused analysis on the largest subcortical targets of primary visual cortex: the superior colliculus (SC), the dorsal lateral geniculate nucleus of the thalamus (dLGN), and the lateral division of the lateral posterior nucleus of the thalamus (LPL). We found that localized cooling of different regions of primary visual cortex caused specific decreases in 2DG uptake in target structures such that the location of 2DG decrease varied according to joint retinotopy, and the magnitude of the decreases in target structures was associated with the amount of cooled cortex. In addition, we found that the impact of cortical cooling was more profound on the SC than on the dLGN. The functional impact of cortical deactivations on the LPL was weak for small deactivations but approximated the impact on the SC when deactivations were large. We discuss these findings in terms of neural circuits and in terms of drivers and modulators.

Animals↗
PubMed2000

Lateral spike conduction velocity in the visual cortex affects spatial range of synchronization and receptive field size without visual experience: a learning model with spiking neurons.

Classical receptive fields (cRF) increase in size from the retina to higher visual centers. The present work shows how temporal properties, in particular lateral spike velocity and spike input correlation, can affect cRF size and position without visual experience. We demonstrate how these properties are related to the spatial range of cortical synchronization if Hebbian learning dominates early development. For this, a largely reduced model of two successive levels of the visual cortex is developed (e.g., areas V1 and V2). It consists of retinotopic networks of spiking neurons with constant spike velocity in lateral connections. Feedforward connections between level 1 and 2 are additive and determine cRF size and shape, while lateral connections within level 1 are modulatory and affect the cortical range of synchronization. Input during development is mimicked by spike trains with spatially homogeneous properties and a confined temporal correlation width. During learning, the homogeneous lateral coupling shrinks to limited coupling structures defining synchronization and related association fields (AF). The size of level-1 synchronization fields determines the lateral coupling range of developing level-1-to-2 connections and, thus, the size of level-2 cRFs, even if the feedforward connections have distance-independent delays. AFs and cRFs increase with spike velocity in the lateral network and temporal correlation width of the input. Our results suggest that AF size of V1 and cRF size of V2 neurons are confined during learning by the temporal width of input correlations and the spike velocity in lateral connections without the need of visual experience. During learning from visual experience, a similar influence of AF size on the cRF size may be operative at successive levels of processing, including other parts of the visual system.

Action Potentials↗
PubMed1994

Feature-linked synchronization of thalamic relay cell firing induced by feedback from the visual cortex.

The function of the massive feedback projection from visual cortex to its thalamic relay nucleus has so far eluded any clear overview. This feedback exerts a range of effects, including an increase in the inhibition elicited by moving contours, but the functional logic of the direct connections to the thalamic cells that relay the retinal input to the cortex remains largely unknown. In contrast to its thalamic nucleus, the visual cortex is characterized by cells that are strongly sensitive to the orientation of moving contours. Here we report that when driven by moving oriented visual stimuli the cortical feedback induces correlated firing in relay cells. This cortically induced correlation of relay cell activity produces coherent firing in those groups of relay cells with receptive field alignments appropriate to signalling the particular orientation of the moving contour to the cortex. Synchronization of relay cell firing means that they will elicit temporally overlapping excitatory postsynaptic potentials in their cortical target cells, thus increasing the chance that the cortical cells will fire. Effectively this increases the gain of the input for feature-linked events detected by the cortex. We propose that this feedback loop serves to lock or focus the appropriate circuitry onto the stimulus feature.

Action Potentials↗
PubMed1988

The distribution and ontogenesis of [3H]nicotine binding sites in cat visual cortex.

In vitro autoradiographic techniques using [3H]nicotine were used to characterise nicotine binding sites in developing kitten visual cortex. These binding sites in adult animals have a Bmax of 3.91 fmol/mg protein and a Kd of 4.40 nM. Displacement experiments indicate that [3H]nicotine binds to a nicotinic receptor site that is similar to central nicotinic sites described by investigators in other mammals. The number of binding sites increases during postnatal development, peaking near 60 days of age and levelling-off thereafter. There is no evidence for large changes in affinity during postnatal development for this binding site. [3H]Nicotine binding sites are densely concentrated in layer IV in the visual cortex of adult animals, with sharply reduced binding outside of cortical areas 17 and 18. This laminar pattern does not change during postnatal development, but an increase in the number of binding sites in layer IV as well as in layers I and VI occurs during early postnatal life. These binding sites disappear when extrinsic cortical inputs are severed. However, they survive when neurons in the visual cortex are selectively destroyed with a cell-specific neurotoxin. Unilateral destruction of the lateral geniculate nucleus eliminates [3H]nicotine binding sites in the visual cortex ipsilateral to the lesion, suggesting that they are located presynaptically on the terminals of lateral geniculate nucleus afferent fibres. The laminar pattern of binding of [3H]nicotine during early development of the visual cortex is complimentary to that for muscarinic acetylcholine receptors. These latter receptors redistribute during postnatal development becoming less prominent in layer IV at the same time as the [3H]nicotine binding sites are increasing in number in this layer. For a short period of time at the height of the critical period for cortical plasticity, both populations of binding sites are located in layer IV.

Animals↗
PubMed1990

Electrophysiological properties of embryonic neocortex transplants replacing the primary visual cortex of adult rats.

Solid pieces of the occipital neocortex derived from 17-day rat fetuses were placed in a cavity formed by complete unilateral aspiration of the primary visual cortex in adult rats. Vital labeling of the brain with bisbenzimide was used to differentiate grafts from the host brain tissue. 2 to 10 months after operation electrophysiological experiments were performed in which neuronal activity and field potentials in transplants were recorded in response to sensory and electrical stimulation of the host brain. This study shows that in a large portion of the transplants (14 out of 25): (1) the majority of neurons (183/270) are controlled by visual stimuli and many of them respond to electrical stimulation of the lateral geniculate body (53/62) and the homotopic sites of the contralateral neocortex (28/62); latencies of these responses are within the ranges typical of the normal visual cortex; (2) there is a topical representation of the visual field on the transplants; (3) receptive field sizes, the preference to stationary flashes or to moving visual stimuli and the temporal response pattern of the grafted neurons are similar to those of the primary visual cortex. However, the field potentials evoked visually were recorded only in part of the transplants (8/14) which revealed clear neuronal visual responses, and field potential depth profile differed from that in visual cortex in situ. The functional organization of the transplants remained unchanged throughout the long-time testing. Taken together, these results suggest that after primary visual cortex removal, fetal neocortex transplants may be able to replace functionally the damaged neural circuitries of the host brain.

Animals↗
PubMed2000

[Spatial frequency tuning characteristics of cat primary visual cortex at different topological locations by optical imaging].

Using optical imaging based on intrinsic signals, we studied spatial frequency tuning characteristics of cat primary visual cortex at different visual topological locations. We found that the areas representing the peripheral visual field had null or very weak responses to high spatial frequency grating stimuli, whereas the areas representing the central visual field responded to the stimuli of a wide range of spatial frequencies with greater responses to high spatial frequencies. The more centered the corresponding visual field of the cortical area, the higher the cutoff spatial frequency. The spatial frequency tuning curves also tended to have a smooth shift along the cortical surface. The results above demonstrate that spatial frequency tuning characteristics of the primary visual cortex change according to different visual topological locations of the cortical areas, in addition to the existence of spatial frequency columns. It is suggested that the distribution of spatial frequency columns may be related to visual topology.

Animals↗
PubMed1995

gamma-Aminobutyric acid and somatostatin immunoreactivity in the visual cortex of normal and dark-reared rats.

Our previous single unit and ultrastructural studies of visual cortex of dark-reared rats revealed an impairment of intracortical inhibitory mechanisms [2,3,5]. Neurochemical changes in inhibitory neurotransmitter and/or neuropeptides, such as gamma-aminobutyric acid (GABA) and somatostatin (SS), respectively, may contribute to the observed alterations. The present study was designed to measure GABA and SS alterations in the visual cortex of the same dark-reared preparation, as possible neurochemical correlates of the changes seen both physiologically and anatomically in previous companion studies. In the present investigation the mean densities of GABA- and SS-immunoreactive neurons in area 17 of dark-reared rats were determined and compared to the density of those of rats reared in normal lighting conditions. Dark-rearing resulted in a significant decrease in the density of GABA-immunoreactive neurons in all cell layers of area 17 of the rat visual cortex; not limited to the thalamorecipient layer(s). There was also a higher mean density of total cortical cells in dark-reared animals. No differences, however, were seen in the density of SS-immunoreactive neurons. The alterations of GABA-immunoreactive neurons in all cortical layers agree with the altered synaptic ultrastructure and physiological responses seen in all cortical layers as reported in our previous companion studies. Taken together, these studies further support the notion of a deficit in intracortical inhibitory mechanisms in the visual cortex of dark-reared adult rats.

Animals↗
PubMed1993

Histochemical localization of synaptic zinc in the developing cat visual cortex.

The terminal boutons of many neurons in the telencephalon are known to contain a vesicle-bound, chelatable pool of zinc (Zn2+) that can be selectively visualized with histochemical procedures. In this paper, the normal laminar, areal, and ultrastructural distribution of histochemically reactive zinc in the visual cortex of the adult cat as well as its development from birth are described. In the adult cat visual cortex, intense zinc staining was found in layers I, II, III, and V, with layer VI staining only lightly. The primary geniculostriate input zone, layer IV, was conspicuously distinguished by the relative absence of zinc. This distinct pattern was restricted only to areas 17 and 18 and differentiated them from adjacent cortical area 19 laterally and the subadjacent cingulate cortex. The earliest zinc-positive staining in visual cortical areas 17 and 18 was first apparent by postnatal day 2 (P2) and was characterized by staining of a thin layer at the bottom of the cortical plate. By P10, and continuing through P20, synaptic zinc formed a trilaminar pattern of dense staining in areas 17 and 18, which included the top of layer I, and layers III and V. The laminar pattern of synaptic zinc in visual cortex appeared mature by P30, except that the distribution of zinc in layer IV was not uniform. This was most apparent around P50 in tangential sections through layer IV from opened and flattened cortex, where columnar patches of increased zinc staining were apparent in area 17. These columns were approximately 400 microns in diameter, with a centre-to-centre spacing of approximately 900 microns. The distribution of synaptic zinc apparently reflects the process of synaptic maturity of the cat visual cortex and appears to demarcate a particular form of columnar organization in visual cortex.

Animals↗
PubMed2002

Expression of the nerve growth factor receptors TrkA and p75NTR in the visual cortex of the rat: development and regulation by the cholinergic input.

Several lines of evidence have shown that nerve growth factor (NGF), the progenitor of the neurotrophin family of growth factors, plays a fundamental role in the developmental plasticity of the rat visual cortex. However, the expression of NGF receptors (NGFRs) TrkA and p75(NTR) and the possible sites of NGF action in the visual cortex remain to be elucidated so far. Using a highly sensitive ECL immunoblot analysis, we have been able to show, in the present study, that the TrkA protein is expressed in the rat visual cortex and that it is developmentally upregulated during the critical period for cortical plasticity. In contrast, the expression level of the low-affinity NGF receptor p75(NTR) seems to remain nearly constant throughout development. In the analysis of possible pathways involved in the regulation of NGFR expression, we found that neither blockade of the visual input nor NGF administration to the visual cortex resulted in a modulation of NGFR levels of expression. On the other hand, the selective destruction of cholinergic afferents to the visual cortex caused a dramatic, but not complete, reduction of the cortical NGFRs, which suggests that these receptors are located on cholinergic terminals predominantly. At the functional level, we found that, after the elimination of the cholinergic afferents to the visual cortex, the NGF-induced increase of both acetylcholine and glutamate release from cortical synaptosomes was strongly impaired. These results indicate that the cholinergic input is an important mediator of visual cortex responsiveness to NGF action.

Acetylcholine↗
PubMed2005

Modeling the spatiotemporal cortical activity associated with the line-motion illusion in primary visual cortex.

Our large-scale computational model of the primary visual cortex that incorporates orientation-specific, long-range couplings with slow NMDA conductances operates in a fluctuating dynamic state of intermittent desuppression (IDS), which captures the behavior of coherent spontaneous cortical activity, as revealed by in vivo optical imaging based on voltage-sensitive dyes. Here, we address the functional significance of the IDS cortical operating points by investigating our model cortex response to the Hikosaka line-motion illusion (LMI) stimulus-a cue of a quickly flashed stationary square followed a few milliseconds later by a stationary bar. As revealed by voltage-sensitive dye imaging, there is an intriguing similarity between the cortical spatiotemporal activity in response to (i) the Hikosaka LMI stimulus and (ii) a small moving square. This similarity is believed to be associated with the preattentive illusory motion perception. Our numerical cortex produces similar spatiotemporal patterns in response to the two stimuli above, which are both in very good agreement with experimental results. The essential network mechanisms underpinning the LMI phenomenon in our model are (i) the spatiotemporal structure of the LMI input as sculpted by the lateral geniculate nucleus, (ii) a priming effect of the long-range NMDA-type cortical coupling, and (iii) the NMDA conductance-voltage correlation manifested in the IDS state. This mechanism in our model cortex, in turn, suggests a physiological underpinning for the LMI-associated patterns in the visual cortex of anaesthetized cat.

Animals↗
PubMed2000

Reduction of human visual cortex excitability using 1-Hz transcranial magnetic stimulation.

The effects of low-frequency (1-Hz) repetitive transcranial magnetic stimulation on visual cortex excitability were investigated by measuring phosphene thresholds (PTs) and stimulus-response curves. Stimulation over the visual cortex led to significantly decreased visual cortex excitability, expressed as an increase in PT. The motor threshold of the hand muscles did not change, indicating the topographic specificity of this effect. This intervention may be useful in situations associated with a hyperexcitable visual cortex.

Adult↗
PubMed1987

GABA immunoreactive neurons in rat visual cortex.

An antiserum to gamma-aminobutyric acid (GABA) was used in a light and electron microscopic immunocytochemical study to determine the morphology and distribution of GABA-containing neurons in the rat visual cortex and to ascertain whether all classes of nonpyramidal neurons in this cortex are GABAergic. The visual cortex used for light microscopy was prepared in such a way that the antibody penetrated completely through tissue sections, and in these sections large numbers of GABA immunoreactive neurons were apparent. The labeled neurons could be identified as being either multipolar, bitufted, bipolar, or horizontal neurons. In layers II through VIa, GABA immunostained cells were distributed uniformly and accounted for approximately 15% of all neurons, but in layer I all neurons appeared to be immunostained. Electron microscopy of GABA immunostained visual cortex prepared to ensure good fine structural preservation confirmed the presence in layers II through VIa of numerous immunoreactive bipolar neurons, both small and large varieties, as well as multipolar and bitufted neurons. Additionally, electron microscopy reveals that astrocytes are frequently GABA immunoreactive. From a correlated light and electron microscopic evaluation of neurons in GABA immunostained visual cortex, it was possible to confirm which kinds of neurons are GABAergic and what proportion of the neuronal population they represent. Thus, from an analysis of some 950 neurons, it was found that pyramidal neurons were never immunoreactive and that except for 20% of the bipolar cell population, all examples of other types of nonpyramidal neurons encountered in this material were GABA immunoreactive.

Animals↗
PubMed1986

The structure and symmetry of simple-cell receptive-field profiles in the cat's visual cortex.

Receptive fields of simple cells in the cat visual cortex have recently been discussed in relation to the 'theory of communication' proposed by Gabor (1946). A number of investigators have suggested that the line-weighting functions, as measured orthogonal to the preferred orientation, may be best described as the product of a Gaussian envelope and a sinusoid (i.e. a Gabor function). Following Gabor's theory of 'basis' functions, it has also been suggested that simple cells can be categorized into even- and odd-symmetric categories. Based on the receptive field profiles of 46 simple cells recorded from cat visual cortex, our analysis provides a quantitative description of both the receptive-field envelope and the receptive-field 'symmetry' of each of the 46 cells. The results support the notion that, to a first approximation, Gabor functions with three free parameters (envelope width, carrier frequency and carrier phase) provide a good description of the receptive-field profiles. However, our analysis does not support the notion that simple cells generally fit into even- and odd-symmetric categories.

Animals↗
PubMed1988

Surgical undercutting prevents receptor redistribution in developing kitten visual cortex.

Recent studies have shown that several receptor populations in cat visual cortex undergo alterations in their laminar distributions during postnatal development (Shaw et al., 1984a,b; 1986b). These redistributions occur during the first few months of postnatal life, coincident with the physiologically defined critical period for cortical plasticity. In the present communication, we demonstrate that receptor redistributions can be prevented from occurring, or progressing once started, by surgically isolating the visual cortex at appropriate postnatal ages. These data suggest that the maturation of the chemical circuitry of the visual cortex is dependent on factors of extrinsic origin.

Animals↗
PubMed1983

Frequency specific effects of stroboscopic rearing in the visual cortex of the rabbit.

Rearing animals in stroboscopic illumination deprives those animals of the experience of visual motion. In the rabbit, stroboscopic rearing produces a significant alteration in the response properties of cells in the visual cortex, demonstrating that the rabbit visual system is susceptible to environmental manipulation during early postnatal life. Response properties were determined for single units recorded in the primary visual cortex of 3 groups of rabbits. One group had been reared from birth to 2 months of age at a stroboscopic flash frequency of 8 Hz, a second group was raised at a flash frequency of 4 Hz and a third was reared normally. Compared to normal rabbits, rabbits reared at 8 Hz showed a reduction in the proportion of orientation selective cells which were also direction-selective, and there was an increase in the proportion of cells responsive to stroboscopic flashes. There was no reduction, however, in the overall proportion of orientation-selective cells. This contrasts with the finding for the rabbits raised at a flash frequency of 4 Hz. In addition, cortical cells in the rabbits raised at 8 Hz responded to frequencies of stroboscopic flashes which were significantly higher than the frequencies found for cells in the rabbits raised at 4 Hz. The effects of stroboscopic rearing on the rabbit visual cortex are dependent, therefore, on the flash frequency experienced by the rabbits during development.

Animals↗