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PubMed1984

[Activity of neurons of the somatosensory and visual cortex in the rabbit during visual field testing and performance of food-getting behavior].

The activity of somatosensory and visual cortex neurons was compared in experiments on freely moving rabbits during testing of their receptive field and during natural "stimulation" of the receptive areas by environmental objects in food-acquisition behaviour. It was found that the neuronal activity during the receptive field testing may correspond completely, partly or not at all to that in food-acquisition behaviour, i.e. units displaying a certain relation to a receptive field area during the testing may keep it unaltered, alter it or lose it in food-acquisition behaviour. The different activity in the behaviour was observed even in neurons having identical receptive fields during testing. A conclusion is made that the picture of unit activity in the active goal-directed behaviour being modelled on the basis of receptive field testing may be rather vague. The results of experiments with the receptive field testing may help to develop the concept of processing of information about environment in the behaviour but with some limitations whose formulation demands special investigations.

Animals↗
PubMed2006

Retinal waves trigger spindle bursts in the neonatal rat visual cortex.

During visual system development, the light-insensitive retina spontaneously generates waves of activity, which are transmitted to the lateral geniculate nucleus. The crucial question is whether retinal waves are further transmitted to the cortex and influence the early cortical patterns of activity. Using simultaneous recordings from the rat retina and visual cortex during the first postnatal week in vivo, we found that spontaneous retinal bursts are correlated with spindle bursts (intermittent network bursts associated with spindle-shape field oscillations) in the contralateral visual cortex (V1). V1 spindle bursts could be evoked by electrical stimulation of the optic nerve. Intraocular injection of forskolin, which augments retinal waves, increased the occurrence of V1 spindle bursts. Blocking propagation of retinal activity, or removal of the retina reduced the frequency, but did not completely eliminate the cortical spindle bursts. These results indicate that spontaneous retinal waves are transmitted to the visual cortex and trigger endogenous spindle bursts. We propose that the interaction between retinal waves and spindle bursts contributes to the development of visual pathways to the cortex.

Action Potentials↗
PubMed2000

Differential distribution of barrel or visual cortex. Evoked responses along the rostro-caudal axis of the peri- and postrhinal cortices.

The functional connections between the barrel cortex and visual cortex on the one hand and the perirhinal (PER) and postrhinal (POR) cortices on the other hand were investigated in the rat. Stimulation of the barrel cortex evoked field potentials throughout the longitudinal extent of both PER and POR. In contrast, visual cortex stimulation evoked responses only in the caudal portion of PER as well as in POR. Therefore, the information from the visual cortex on the way to the hippocampus is transferred preferentially by a relay in POR, whereas somatosensory information is transferred via both PER and POR. Moreover, stimulation of both cortical regions elicited firing of multiple units; however, unit activity was more commonly found in POR than in PER. We conclude that the transfer of somatosensory and visual information to the hippocampal formation is preferentially mediated by parallel channels through PER and POR respectively. Although the information transfer through these channels does overlap to some extent, each channel appears to have specific properties.

Action Potentials↗
PubMed2005

Organization of horizontal axons in the inferior temporal cortex and primary visual cortex of the macaque monkey.

We investigated the organization of horizontal connections at two distinct hierarchical levels in the ventral visual cortical pathway of the monkey, the inferior temporal (TE) and primary visual (V1) cortices. After injections of anterograde tracers into layers 2 and 3, clusters of terminals ('patches') of labeled horizontal collaterals in TE appeared at various distances up to 8 mm from the injection site, while in V1 clear patches were distributed only within 2 mm. The size and spacing of these patches in TE were larger and more irregular than those observed in V1. The labeling intensity of patches in V1 declined sharply with distance from the injection site. This tendency was less obvious in TE; a number of densely labeled patches existed at distant sites beyond weakly labeled patches. While injections into both areas resulted in an elongated pattern of patches, the anisotropy was greater in TE than in V1 for injections of a similar size. Dual tracer injections and larger-sized injections further revealed that the adjacent sites in TE had spatially distinct horizontal projections, compared to those in V1. These area-specific characteristics of the horizontal connections may contribute to the differences in visual information processing of TE and V1.

Animals↗
PubMed2002

Differential expression of c-fos in subtypes of GABAergic cells following sensory stimulation in the cat primary visual cortex.

Recent immunocytochemical stainings on cat visual cortex, visually stimulated for 1 h, showed a strong induction of Fos expression in cortical neurons. We initiated immunocytochemical double staining experiments with different cytochemical markers to investigate the neurochemical and morphological character of these activated neurons showing Fos induction after sensory stimulation. Double staining with Fos and glutamic acid decarboxylase (GAD) demonstrated the presence of Fos in the nuclei of GABAergic neurons of the primary visual cortex. To further subdivide this Fos/GABAergic cell population we investigated whether Fos colocalized with parvalbumin, calbindin or calretinin. Colocalization of Fos with these calcium-binding proteins delineated distinct neuronal subclasses of Fos-immunoreactive neurons in supra- and infragranular layers of cat area 17. Quantitative analysis of the proportion of immunoreactive local circuit neurons revealed that 35% of the GABAergic neurons showed Fos induction in supragranular layers, whereas in infragranular layers a mere 10% of the GABAergic cells revealed Fos expression. Fos coexisted in about 24% of the calbindin-immunopositive cells within supra- and infragranular layers, but only a minority of the parvalbumin and the calretinin neuronal subgroups were immunopositive for Fos in the corresponding layers of area 17. These findings suggest that visual stimulation induces Fos expression in distinct subsets of inhibitory neurons in cat primary visual cortex.

Animals↗
PubMedDate not supplied

Connectivity of GABAergic calretinin-immunoreactive neurons in rat primary visual cortex.

In rat visual cortex neurons that are immunoreactive for the calcium-binding protein calretinin (CR+) constitute a distinct family which accounts for 17% of gamma-aminobutyric acid (GABA)-expressing cells. It is not clear, however, (i) whether CR is expressed exclusively in GABAergic neurons and (ii) how CR+ neurons are incorporated into neuronal circuits of rat visual cortex. To address these questions we studied synaptic relationships of CR+ neurons with GABA+ and GABA- elements in the neuropil of rat primary visual cortex (area 17). All CR+ neurons are nonpyramidal cells with smooth or sparsely spiny and often beaded dendrites. Of all CR+ neurons, 56% are located in layers 1 and 2/3. In layer 2/3, most CR+ neurons are bipolar-shaped and have vertically oriented dendrites. Many ascending dendritic branches reach layer 1 where they run parallel to pial surface. CR+ axons are thin, highly branched near the cell body and often send descending collaterals to layers 5 and 6. Double immunofluorescence labeling revealed GABA in 94% of CR+ cell bodies in layer 2/3. Electron microscopic analysis shows that all CR+ axon terminals contain elongated vesicles and form symmetric synapses. Postembedding staining shows that 98% of CR+ terminals are GABA+. GABA-immunoreactivity is also present in somata and thick dendrites of CR+ neurons but many thin dendrites are GABA-. CR+ somata, dendrites and axon terminals are enriched in mitochondria. Somata and thick CR+ dendrites are densely innervated. At least 68% of the targets of CR+ terminals in layer 2/3 are GABA+ and > or = 50% of these are other CR+ neurons. The remainder (32%) of targets of CR+ terminals are thin dendrites of GABA- cells. In contrast, in layers 5 and 6, 60% of CR+ terminals form synapses with GABA- somatic profiles. The preferential interactions of layer 2/3 CR+ neurons with GABAergic neurons, and with CR+ neurons in particular, suggests that these cells play a role in the inhibition of inhibitory neurons of the same layer. Through these interactions CR+ cells may reduce inhibition of pyramidal cells in layers 2/3, 5 and 6 and thus disinhibit a column of neurons.

Animals↗
PubMed2006

High-frequency activity in human visual cortex is modulated by visual motion strength.

A central goal in systems neuroscience is to understand how the brain encodes the intensity of sensory features. We used whole-head magnetoencephalography to investigate whether frequency-specific neuronal activity in the human visual cortex is systematically modulated by the intensity of an elementary sensory feature such as visual motion. Visual stimulation induced a tonic increase of neuronal activity at frequencies above 50 Hz. In order to define a functional frequency band of neuronal activity, we parametrically investigated which frequency band displays the strongest monotonic increase of responses with strength of visual motion. Consistently in all investigated subjects, this analysis resulted in a functional frequency band in the high gamma range from about 60 to 100 Hz in which activity reliably increased with visual motion strength. Using distributed source reconstruction, we found that this increase of high-frequency neuronal activity originates from several extrastriate cortical regions specialized in motion processing. We conclude that high-frequency activity in the human visual motion pathway may be relevant for encoding the intensity of visual motion signals.

Adult↗
PubMed1983

Effects of lateral suprasylvian visual cortex lesions on visual localization, discrimination, and attention in cats.

Experiments were carried out to begin to define the behavioral functions of the lateral suprasylvian (LS) visual area of the cat's cortex. Behavioral tasks were chosen for analysis on the basis of previous suggestions in the literature concerning possible functions of LS cortex and its afferent pathways. These tasks included the ability of cats to orient the head and eyes to a stimulus presented in particular locations in the visual field, the ability to learn successive reversals of a two-choice visual pattern discrimination, and the ability to maintain or shift attention between relevant or irrelevant visual form and brightness cues. Eight cats were trained on each of these tasks. Four of the cats then received bilateral lesions of LS cortex, including the AMLS and PMLS regions, and the remaining 4 cats were used to assess normal retention. The LS cortex lesions had no significant effect upon performance of any of the behaviors tested. Thus, this region of cortex appears to play no essential role in simple brightness, form, and pattern discrimination performance, visual reversal learning, maintaining and shifting visual attention, or orienting the head and eyes to stimuli in the visual field. These results are discussed in relation to previous lesion studies involving large regions of the cat's extrastriate cortex and studies in other species. Possible functions of LS cortex, based upon recent electrophysiological studies, are suggested.

Animals↗
PubMed1999

Matching the modules: cortical maps and long-range intrinsic connections in visual cortex during development.

Visual cortical neurons exhibit a high degree of response selectivity and are grouped into small columns according to their response preferences. The columns are located at regularly spaced intervals covering the whole cortical representation of the visual field with a modular system of feature-selective neurons. The selectivity of these cells and their modular arrangement is thought to emerge from interactions in the network of specific intracortical and thalamocortical connections. Understanding the ontogenesis of this complex structure and contributions of intrinsic and extrinsic, experience-dependent mechanisms during cortical development can provide new insights into the way the visual cortex processes information about the environment. Available data about the development of connections and response properties in the visual cortex suggest that maturation proceeds in two distinct steps. In the first phase, mechanisms inherent to the cortex establish a crude framework of interconnected neural modules which exhibit the basic but still immature traits of the adult state. Relevant mechanisms in this phase are assumed to consist of molecular cues and patterns of spontaneous neural activity in cortical and corticothalamic interconnections. In a second phase, the primordial layout becomes refined under the control of visual experience establishing a fine-tuned network of connections and mature response properties.

Animals↗
PubMed1996

Interareal synchronization in the visual cortex.

The primary visual cortex (V1) is part of a highly interconnected network of cortical areas, hierarchically organized but operating concurrently across hierarchical levels. The high degree of reciprocal interconnection among visual cortical areas provides a framework for their interaction during the performance of visual scene analysis. The functional interdependency of visual cortical areas which develops during scene analysis can be investigated by techniques which measure interareal correlated activity. Evidence from monkeys performing a visual pattern discrimination suggests that synchronization of aperiodic activity from neuronal ensembles in cortical areas at different hierarchical levels is a relevant aspect of visual function. The near-periodic nature of the synchronized response to moving light bars in earlier studies may have been a result of the type of stimulus used. Various models of visual cortex are discussed in which interareal synchronization plays a functional role.

Animals↗
PubMed1994

Functional postnatal development of the rat primary visual cortex and the role of visual experience: dark rearing and monocular deprivation.

Postnatal development of rat visual cortical functions was studied by recording extracellularly from the primary visual cortex of 22 animals ranging in age from postnatal day 17 (P17) to P45. We found that in the youngest animals (P17-P19) all visual cortical functions tested were immature. Selectivity for orientation and movement direction of visual stimuli was almost absent, most cells received binocular input and their mean receptive field size was 5-6 times the adult size. Visual acuity was half its adult value. These functional properties developed gradually during the following weeks and by P45 they were all adult-like. This functional development is affected by manipulations of the visual input such as dark rearing (DR) and monocular deprivation (MD). DR prevented the normal postnatal maturation of visual cortical functions: in P60 rats, dark reared from birth, their visual cortical functions resembled those of P19-P21 rats. MD from P15 to P45 resulted in a dramatic shift of the ocular dominance distribution (ODD) in favour of the open eye and in a loss of visual acuity for the deprived eye. To determine the sensitive period of rat visual cortex to MD (critical period) we evaluated the shift in ODD of visual cortical neurones in rats that were subjected to the progressive delay of the onset of fixed MD period (10 days). Our results show that the critical period begins around the end of the third postnatal week, peaks between the fourth and fifth week and starts to decline from the end of the fifth week.

Age Factors↗
PubMed1998

Spatial and temporal differentiation of fMRI BOLD response in primary visual cortex of human brain during sustained visual simulation.

The blood oxygenation level dependent (BOLD) response during sustained visual stimulation has been studied by several groups using fMRI with controversial conclusions. This issue was investigated for the human brain at high (4 Tesla) magnetic field strength using a flashing goggle at 8 Hz. The results demonstrate that the overall BOLD response in the primary visual cortex has an initial overshoot after the onset of visual stimulation and an undershoot after the termination of visual stimulation. A significant and positive BOLD response, however, remains constant between the initial and terminal transient responses. The temporal BOLD responses in the primary visual cortex were spatially dependent. The regions identified as draining veins in images displayed proportionately larger initial and terminal transient responses, whereas regions devoid of such vessels and associated mainly with parenchyma exhibited a more time-independent BOLD response. These results reveal that the BOLD effect and, presumably, the uncoupling between cerebral blood flow and cerebral metabolic rate of oxygen consumption, are maintained in the primary visual cortex during sustained visual stimulation, and the temporal characteristics of the BOLD effect are spatially dependent.

Humans↗
PubMedDate not supplied

Electrophysiological correlates of hyperacuity in the human visual cortex.

The human visual system is capable of detecting a vernier misalignment with extraordinary accuracy. Since this remarkable precision in spatial localization is better than can be naively predicted by simple optical or anatomical considerations it has been termed a hyperacuity. So far no single neurone model seems capable of accounting for hyperacuity, and the retinal image might require reconstitution in a finer grained from in the visual cortex. We report here an electrophysiological correlate of hyperacuity recorded from the human visual cortex. The amplitude of the visually evoked potentials (v.e.ps) elicited by the appearance of a vernier offset varied systematically with the magnitude of the offset. Extrapolation of the function relating v.e.p. amplitude and log offset to zero voltage resulted in an electrophysiological estimate of vernier acuity that was similar to the observer's psychophysical threshold.

Electroencephalography↗
PubMed2002

Clustered organization of neurons with similar extra-receptive field properties in the primary visual cortex.

The primary visual cortex is organized into clusters of cells having similar classical receptive field (CRF) properties. Nonclassical, extra-receptive fields (ERFs) can either inhibit or facilitate the response elicited by stimulation within the CRF. Here, we report that in the primary visual cortex of cat, neurons with similar inhibitory or facilitatory ERF properties are also grouped into clusters. These clusters are randomly distributed in all cortical layers, with no detectable relationship with orientation and ocular dominance columns. This functional organization of neurons with respect to ERF properties may allow an efficient processing of global visual information.

Action Potentials↗
PubMed2001

Suppression of cortical NMDA receptor function prevents development of orientation selectivity in the primary visual cortex.

Selectivity to visual stimulus orientation is a basic cortical functional property believed to be crucial for normal vision. Maturation of this neuronal property requires neural activity. Still, it is unclear what might be the molecular basis for such activity-dependent processes and whether activity has an instructive or permissive role in development of orientation selectivity. There is strong evidence that the NMDA subtype of the glutamate receptor regulates activity-dependent mechanisms of ocular dominance plasticity during cortical development. For this reason, we have hypothesized that the NMDA receptor participates in activity-dependent mechanisms that sculpt orientation selectivity of cortical neurons. We used chronic in vivo infusion of antisense oligodeoxynucleotides (ODNs) to suppress NMDA receptor function in primary visual cortex during the period when orientation selectivity develops in ferrets. Chronic suppression of NMDA receptor function prevented the development of orientation and stimulus size selectivity in most cortical cells tested. In contrast, treatment with control sense or missense ODNs did not affect development of orientation selectivity, indicating specificity of effects. Importantly, antisense ODN treatment did not impair visually driven activity, which is required for development to occur. Moreover, orientation selectivity of cortical cells was not disrupted by antisense ODN treatment in mature animals, indicating developmental relevance of the effects. In conclusion, our findings document for the first time that cortical NMDA receptors are essential for the maturation of orientation selectivity. This result supports the notion that activity has an instructive role in sculpting the connections that underlie orientation selectivity in visual cortex.

Aging↗
PubMed1997

Increase of creatine kinase activity in the visual cortex of human brain during visual stimulation: a 31P magnetization transfer study.

31P magnetic resonance spectroscopy was used to investigate changes in high energy phosphate levels and creatine kinase (CK) kinetics induced in the human visual cortex during photic stimulation. CK kinetics was evaluated by measuring the apparent unidirectional rate constant (kf) in the "forward" direction (i.e., in the direction of ATP synthesis from phosphocreatine). kf increased 34% in the visual cortex areas during stimulation without significant changes of steady-state concentration of high energy phosphate compounds, indicating that CK turnover is elevated during increased neuronal activity.

Adenosine Triphosphate↗
PubMed2000

Activity in primary visual cortex predicts performance in a visual detection task.

Visual attention can affect both neural activity and behavior in humans. To quantify possible links between the two, we measured activity in early visual cortex (V1, V2 and V3) during a challenging pattern-detection task. Activity was dominated by a large response that was independent of the presence or absence of the stimulus pattern. The measured activity quantitatively predicted the subject's pattern-detection performance: when activity was greater, the subject was more likely to correctly discern the presence or absence of the pattern. This stimulus-independent activity had several characteristics of visual attention, suggesting that attentional mechanisms modulate activity in early visual cortex, and that this attention-related activity strongly influences performance.

Action Potentials↗
PubMed1999

A new form of synaptic plasticity is transiently expressed in the developing rat visual cortex: a modulatory role for visual experience and brain-derived neurotrophic factor.

Synaptic plasticity has been implicated in the mechanisms contributing to the shaping of the cortical circuits responsible for the transmission of the visual input in the rat primary visual cortex. However, the degree of plasticity of the thalamocortical synapse may change during development, perhaps reflecting the degree of stabilization of the circuitry subserving it. We have chosen the ability of this synapse to be first depressed and then potentiated as a specific indicator of its plasticity. In this study we have investigated how this parameter changes during development and the factors controlling it. Extracellular field potentials in cortical layers 2/3 were evoked by stimulation of the white matter in rat primary visual cortex slices prepared at different postnatal ages. Low-frequency stimulation (900 pulses at 1 Hz) of the white matter was used to induce long-term depression of field potential amplitude, whereas long-term potentiation was evoked by high-frequency stimulation consisting of three trains at 100 Hz. We provide evidence that while it is possible to potentiate previously depressed synapses soon after eye opening (postnatal day 17) this synaptic characteristic decreases rapidly thereafter. The decrease in this form of cortical synaptic plasticity closely matches the stabilization of the cortical circuitry towards an adult pattern of connectivity and function. Depressed cortical synapses cannot be potentiated in normal rats at postnatal 23, but they can be potentiated in rats reared in the dark from postnatal days 17 to 29. Moreover, application of brain-derived neurotrophic factor, known to be expressed in an activity-dependent manner, was able to restore the ability of synapses to be potentiated after long-term depression, thus indicating its important modulatory role in brain development.

Animals↗