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PubMed1995

Overall pattern of callosal connections in visual cortex of normal and enucleated cats.

The effect of neonatal bilateral enucleation on the overall distribution of callosal connections in striate and extrastriate visual cortex of the cat was studied using tangential sections from the physically unfolded and flattened cortex. Callosal neurons were labeled by administering the anatomical tracer horseradish peroxidase directly to the transected corpus callosum. The pattern of callosal connections in binocularly enucleated cats showed both consistent differences and consistent similarities with the pattern in normal cats. In agreement with previous studies, it was found that callosal labeling at the 17/18 border of enucleated cats was considerably sparser than in normal cats. Moreover, we found that the strip containing the majority of labeled cells at the 17/18 border was narrower than in normal cats. In both normal and enucleated cats, scattered cells were distributed on either side of the 17/18 callosal strip, well into areas 17 and 18. In much of extrastriate cortex, the pattern of callosal connectivity in enucleated cats looked surprisingly normal. Details of the callosal pattern that were consistently found in normal cats could also be recognized in binocularly enucleated cats, such as two to four bridges of labeling spanning areas 18 and 19. Also, four zones that were free of callosal connectivity in area 7, on the banks of the suprasylvian sulcus, and in the posterior suprasylvian sulcus were found in both normal and enucleated cats. Finally, as in normal cats, dense cell labeling occurred on the crown of the suprasylvian gyrus at its posterior end, from which it extended laterally across both banks of the suprasylvian sulcus and into the fundus of this sulcus. The results of this study suggest that, although the stabilization of callosal connections at the 17/18 border region appears to depend on visual input, this input plays a less prominent role in the stabilization of callosal connections in extrastriate visual cortex.

Animals↗
PubMed1996

Down-regulation of beta-adrenergic receptor following long-term monocular deprivation in cat visual cortex.

To examine how adrenergic receptor binding is modified by experimental manipulation of sensory afferent, we carried out binding experiments (membrane fraction and in vitro autoradiography) for both alpha 2- and beta-adrenergic receptors in the brain of cats which had been deprived of vision in one eye. In the cerebral cortex of control animals, beta-adrenergic receptor (beta-AR) binding was found to be higher in the occipital regions than in other regions, while alpha 2-AR binding was relatively uniform. Monocular deprivation throughout the postnatal sensitive period (1-7 month of age) significantly decreased beta-AR binding in the visual cortex and lateral geniculate nucleus. Scatchard plot analysis in the visual cortex showed ca. 50% reduction in Bmax and little change in Kd. No significant difference was found in alpha 2-AR binding following monocular deprivation. Similar extent of down-regulation in beta-AR binding was confirmed in all layers of visual cortex using autoradiography.

Animals↗
PubMedDate not supplied

Functional importance of alpha-activity in the visual cortex during recognition of images and movement.

Twenty-seven studies were carried out on the recognition of the shapes of geometrical figures of different sizes by healthy adults, on the recognition of the direction of movement of a light spot within the field of vision, and of visual illusions produced by rhythmic visual stimulation. Tachystoscopic presentation of figures and the onset of movement were synchronized with different phases of the EEG alpha-rhythm in the occipital region. In controls, stimuli were presented without a shift in the alpha-rhythm. Recognition improved significantly when small figures were presented at relatively late phases of the alpha-wave and when large figures (up to 9 degrees) were presented at relatively early phases. Recognition of the side and direction of apparent movement (in the left or right halves of the visual field and centrifugal or centripetal) depended on the phase of the alpha-wave only for nonuniform (accelerating or decelerating, depending on direction) movement, allowing for the cortical magnification factor. Centrifugal movements in experiments were recognized better than in controls, while centripetal movements were recognized worse, and elicited a relatively long-latency movement response. Diffuse rhythmic light stimulation at the alpha-rhythm frequency produced the illusory percept of a ring or circle in 11 of 12 subjects. The optimal stimulation frequency for this was tightly connected with the dominant alpha-rhythm frequency, with a correlation coefficient of 0.86. The link between these effects and the propagation of the wave process through the visual cortex, as reflected by the EEG alpha-rhythm, is discussed. The data support the hypothesis of Pitts and McCulloch [29], which proposes scanning of the visual cortex by a wave process operating at the frequency of the alpha-rhythm, which reads information from the visual cortex.

Adult↗
PubMed1998

Local GABA circuit control of experience-dependent plasticity in developing visual cortex.

Sensory experience in early life shapes the mammalian brain. An impairment in the activity-dependent refinement of functional connections within developing visual cortex was identified here in a mouse model. Gene-targeted disruption of one isoform of glutamic acid decarboxylase prevented the competitive loss of responsiveness to an eye briefly deprived of vision, without affecting cooperative mechanisms of synapse modification in vitro. Selective, use-dependent enhancement of fast intracortical inhibitory transmission with benzodiazepines restored plasticity in vivo, rescuing the genetic defect. Specific networks of inhibitory interneurons intrinsic to visual cortex may detect perturbations in sensory input to drive experience-dependent plasticity during development.

Animals↗
PubMed1985

The monoaminergic innervation of the rat visual cortex.

The intracortical distribution of monoamines, noradrenaline (NA) and serotonin (5-HT), was examined in the visual cortex of the rat with high pressure liquid chromatography (h.p.l.c.) and radioautography. H.p.l.c. measurements showed the densities of both amines to be highest in layer I. The concentration of NA varied considerably in all other layers while the 5-HT concentration decreased with increasing distance from the pial surface. The morphological characteristics of the monoaminergic axon-terminals in the cerebral cortex has been the subject of controversy in recent years. We have used radioautography following topical or intraventricular administration of tritiated amines to examine the ultrastructural features of these terminals in the visual cortex of the rat. Systematic analysis of single sections revealed that more than one-half of the terminals labelled with tritiated NA or 5-HT formed typical synaptic contacts (mostly type I) with dendritic shafts or spines.

Animals↗
PubMed1999

Timing of activity in early visual cortex as revealed by transcranial magnetic stimulation.

To determine the timing of visual processing in the early visual cortex, we applied single pulse transcranial magnetic stimulation to the occipital pole of healthy subjects while they were engaged in a forced-choice visual letter-identification task. We found two separate periods of activity, the first ranging from 20 to 60 ms after the onset of the visual stimulus, and the second ranging from 100 to 140 ms after the onset of the visual stimulus. We suggest that these two periods reflect necessary activity in V1, before and after re-entry.

Adult↗
PubMed1997

A family of activity-dependent neuronal cell-surface chondroitin sulfate proteoglycans in cat visual cortex.

Monoclonal antibody Cat-301 recognizes a chondroitin sulfate proteoglycan (CSPG) expressed on the extracellular surface of cell bodies and proximal dendrites of specific subsets of neurons in many areas of the mammalian CNS, including the cat visual cortex. The Cat-301 CSPG is first detected at the close of the critical period in development, a period during which the pattern of neuronal activity determines the mature synaptic circuitry and neuronal phenotype. In the cat visual cortex, dark-rearing from birth prolongs the duration of the critical period and attenuates the expression of the Cat-301 antigen, implicating the Cat-301 CSPG in the cellular mechanisms that terminate the period of synaptic plasticity. Because the Cat-301 antigen is expressed on only a limited subset of neurons, we have further examined the molecular heterogeneity among neuronal cell-surface CSPGs and have asked (1) whether other neuronal subsets carry distinct CSPGs and (2) whether the activity-dependent expression of the Cat-301 CSPG is a property generalizable to related cell-surface CSPGs. Here, we report two new monoclonal antibodies, Cat-315 and Cat-316, which together with Cat-301 define a family of at least seven related yet distinct CSPGs. These three antibodies define nonidentical subsets of neurons in the cat visual cortex. The expression of normal levels of these CSPGs is reduced by dark-rearing. Together, these data show that the family of cell-surface CSPGs is molecularly diverse, that different sets of neurons express distinct complements of cell-surface antigens, and that the regulation of CSPG expression by activity may be a general feature of neuronal cell-surface CSPGs.

Animals↗
PubMed1994

Laminar pattern of synaptic activity in rat primary visual cortex: comparison of in vivo and in vitro studies employing the current source density analysis.

In the present study we employed current source density analysis to study the major excitatory/inhibitory pathways in rat primary visual cortex in vivo and in vitro. A natural photic stimulus was used in vivo and served as a baseline for understanding the results obtained from in vivo and in vitro studies employing electrical stimulation of the white matter. The temporal pattern of synaptic activity in the cortex revealed an early excitation, characterized by sinks of short duration and high amplitude, that was followed by inhibition, characterized by long lasting, low amplitude active sources. The spatial pattern of this synaptic activity displayed early excitatory inputs to layer IV and lower layer III. Supragranular layers exhibited synaptic activity of longer latency at more superficial layers. The excitatory activity of the infragranular layers was delayed relative to that in layer IV. This spatial and temporal pattern of synaptic activity supports the model of sequential information processing in visual cortex. Based on the results of electrical and photic stimulations in vivo we conclude that electrical stimulation of white matter activate the thalamo-cortical input which results in a similar laminar pattern of postsynaptic activity evoked by photic stimulation. Electrical stimulation revealed additional antidromic and anti-orthodromic activity (collaterals of descending axons to white matter), resulting in the early fast components and the additional activity in layer VI. The major differences between in vivo and in vitro laminar pattern of synaptic activity (applying electrical stimulation) were reduced synaptic activity in layer IV and increased synaptic activity in the infragranular layers in the in vitro preparation. We concluded that the visual cortex slice preparation preserves the major pathways and electrophysiological function of this area. The technical advantages of the cortical slice preparation will facilitate studies and provide additional insight into this complex cortical network.

Animals↗
PubMed1997

Three distinct families of GABAergic neurons in rat visual cortex.

In the cortex inhibition is mediated predominantly by GABAergic interneurons. Although all of these neurons use the same neurotransmitter, studies in the rat frontal cortex have shown that they are molecularly and physiologically diverse. It is not known whether similar subgroups of GABAergic neurons exist in primary visual cortex and how these different inhibitory neurons are inserted into specific cortical circuits. We have used immunostaining with antibodies against gamma aminobutyric acid (GABA), parvalbumin (PV), calretinin (CR), somatostatin (SOM), calbindin (CB) and nitric oxide synthase (NOS) to probe for colocalization of known markers of GABAergic interneurons. The results show that the majority of PV (100%), SOM (89.8%) and CR (93.9%) staining neurons are GABA positive. PV immunoreactive neurons constitute a distinct group that show no overlap with CR, SOM and NOS expressing cells and only a minor overlap (5.3%) with CB. PV immunoreactive cells account for 50.8% of GABAergic neurons. A second group of SOM expressing neurons accounts for 16.9% of GABAergic cells. None of these cells colocalize PV or CR, but 1.7% of SOM neurons stain for NOS and 86.3% show CB immunoreactivity. The third distinct group of CR expressing cells accounts for 17.0% of GABAergic neurons. All of these are PV, CB, SOM and NOS negative. CB expressing neurons represent a heterogeneous group that includes GABAergic and non-GABAergic cells. Our findings indicate that GABAergic neurons in rat area 17 are organized in at least three separate families that can be identified by the expression of PV, CR and SOM. These cells account for 84.9% of GABAergic neurons. These results extend previous observations in rat frontal agranular cortex and suggest that in visual cortex the inhibitory network is composed of similar cell types.

Animals↗
PubMed1983

[Study of the functional characteristics of visual cortex neurons in the cat upon local photic stimulation of their receptive fields].

Functional characteristics of 103 neurons in field 17 of the visual cortex were studied in immobilized and unanesthetized cats. Unit responses to modification of local light stimuli wer recorded under conditions of light adaptation. Mean photic threshold of investigated neurons was -32 dB, mean critical temporal summation 57 ms, duration of reactivity recovery 190 ms and sharpness of orientation tuning 37 degrees. As compared to dark adaptation, under light adaptation reduction of light sensitivity, sharpening of orientation tuning as well as a lengthening of temporal summation and a shortening in time of reactivity recovery were observed. A number of neuronal characteristics depended on excentricity of their receptive fields: cells with centrally localized receptive fields had a lower threshold, a short summation and rapid recovery of reactivity; their activity was of higher frequency, and they generated brief transient responses more often than cells with receptive fields in the periphery of a visual field. Mechanisms responsible for change of neuronal properties in the central and peripheral visual channels under light and dark adaptation are discussed. Several inhibitory subsystems are suggested by means of which neuronal activity of the visual cortex is regulated.

Adaptation, Physiological↗
PubMed2005

Local networks in visual cortex and their influence on neuronal responses and dynamics.

Networks of neurons in the cerebral cortex generate complex outputs that are not simply predicted by their inputs. These emergent responses underlie the function of the cortex. Understanding how cortical networks carry out such transformations requires a description of the responses of individual neurons and of their networks at multiple levels of analysis. We focus on orientation selectivity in primary visual cortex as a model system to understand cortical network computations. Recent experiments in our laboratory and others provide significant insight into how cortical networks generate and maintain orientation selectivity. We first review evidence for the diversity of orientation tuning characteristics in visual cortex. We then describe experiments that combine optical imaging of orientation maps with intracellular and extracellular recordings from individual neurons at known locations in the orientation map. The data indicate that excitatory and inhibitory synaptic inputs are summed across the cortex in a manner that is consistent with simple rules of integration of local inputs. These rules arise from known anatomical projection patterns in visual cortex. We propose that the generation and plasticity of orientation tuning is strongly influenced by local cortical networks-the diversity of these properties arises in part from the diversity of neighbourhood features that derive from the orientation map.

Animals↗
PubMed1991

Organization of pyramidal neurons in area 17 of monkey visual cortex.

In sections of area 17 of monkey visual cortex treated with an antibody to MAP2 the disposition of the cell bodies and dendrites of the neurons is readily visible. In such preparations it is evident that the apical dendrites of the pyramidal cells of layer VI form fascicles that pass into layer IV, where most of them gradually taper and form their terminal tufts. In contrast, the apical dendrites of the smaller layer V pyramidal cells come together in a more regular fashion. They form clusters that pass through layer IV and into layer II/III where the apical dendrites of many of the pyramidal cells in that layer add to the clusters. In horizontal sections taken through the middle of layer IV, these clusters of apical dendrites are found to have an average center-to-center spacing of about 30 microns, and it is proposed that each cluster of apical dendrites represents the axis of a module of pyramidal cells that has a diameter of about 30 microns and contains about 142 neurons. The MAP2 antibody reaction also reveals that some pyramidal cells in layers IVA and IVB have their cell bodies arranged into cones. There are about 118 such cones beneath 1 mm2 of cortical surface and the apical dendrites of the pyramidal cells within them bundle together at the apex of each cone to pass into layer III. Surrounding the cones of neurons there are horizontally aligned, thin dendrites. The location of these dendrites coincides with the dark walls of the honeycomb pattern seen in layer IVA after cytochrome oxidase reactions, or after the parvocellular input from the lateral geniculate nucleus has been labeled. Thus the cones of pyramidal cells within upper layer IV fit into the pockets of the honeycomb pattern. Below the cones of pyramidal cells are the outer Meynert cells within layer IVB, and the cell bodies of these large neurons are disposed so that they preferentially lie beneath the neuropil between the cones of pyramids. It is suggested that pyramidal cell modules are a basic feature of the cerebral cortex, and that these are combined together by afferent inputs to the cortex to generate the systems of functional columns.

Animals↗
PubMedDate not supplied

Brain-derived neurotrophic factor alters the synaptic modification threshold in visual cortex.

The effects of brain-derived neurotrophic factor (BDNF) were investigated on synaptic transmission and two forms of activity-dependent synaptic plasticity, long-term potentiation (LTP) and long-term depression (LTD), in visual cortex slices prepared from young (P21 -28) rats. The slices treated for 2-5 h in BDNF showed no difference from control slices when a 'strong' tetanus was used (theta-burst stimulation) to elicit a maximal level of LTP but displayed significantly greater synaptic potentiation in response to a 'weak' (20 Hz) tetanus. The BDNF-treated slices also showed significantly less LTD in response to a 1 Hz tetanus. Thus, BDNF treatment alters the relationship between stimulation frequency and synaptic plasticity in the visual cortex, shifting the modification threshold to the left. The effects of BDNF on LTP and LTD induction may be attributed to the significant enhancement of synaptic responses that was observed during conditioning stimulation. These data suggest that one role of BDNF during development of the visual cortex may be to modulate the properties of synaptic plasticity, enhancing synaptic strengthening and reducing synaptic weakening processes which contribute to the formation of specific synaptic connections.

Animals↗
PubMedDate not supplied

Influence of the posterior hypothalamus on the visual cortex in various states of the reticular formation.

It has been demonstrated in chronic experiments on wakeful rabbits that the stimulation of the posterior hypothalamus by a single electrical stimulus leads to the formation in the visual cortex of a short-latency response which exerts a substantial influence on the formation of the reaction to light stimulation. Depending upon the intervals between the hypothalamic and light stimuli, an initial suppression of the response is observed (1-15 msec), a subsequent selective facilitation of its positive component in the presence of the simultaneous suppression of the negative (20-100 msec), and the complete recovery of the response (200-300 msec). Aminazine and amizil do not alter the directionality of the influence of the stimulation of the posterior hypothalamus on the responses of the visual cortex; however, they do significantly attenuate the degree of expressivity and the dynamics of this influence. Experiments involving local foci in the mesencephalic reticular formation (strychnine, KCl) attest to the inhibitory influence of the latter on the activity of the hypothalamocortical input. The role of the phasic mechanism of hypothalamic control in the realization of the perceptual function of the visual cortex is considered.

Animals↗
PubMed2002

Predicting functional properties of visual cortex from an evolutionary scaling law.

The number of neurons in the primary visual cortex (V1) is, across primate species, related to the number of neurons in the visual thalamus (the lateral geniculate nucleus [LGN]) by a power law with an exponent of 3/2. This evolutionary scaling law is explained by a simple relation according to which the fineness of resolution in cortex is related to the number of neurons in the area of cortex used to process the information from a single point of light (the point-spread area). The same theory provides a link between two functional properties of the visual cortex, the areal cortical magnification factor (ACMF) and the receptive field (RF) area.

Animals↗
PubMed2000

Activation of the visual cortex imaged by 24-channel near-infrared spectroscopy.

Near-infrared spectroscopy (NIRS) is a noninvasive technique for continuous monitoring of the amounts of total hemoglobin (total-Hb), oxygenated hemoglobin, (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb). The purpose of the present study was to demonstrate the utility of NIRS in functional imaging of the human visual cortex. A new NIRS imaging system enabled measurements from 24 scalp locations covering a 9 cm sq area. Topographic images were obtained from interpolations of the concentration changes between measurement points. Five healthy subjects between 25 and 49 years of age were investigated. After a resting baseline period of 50 s, the subjects were exposed to a visual stimulus for 20 s, followed by a 50 s resting period in a dimly lit, sound attenuating room. The visual stimulus was a circular, black and white, alternating checkerboard. In four of five subjects the visual cortex was the most activated area during visual stimulation. This is the first reported use of a NIRS-imaging system for assessing hemodynamic changes in the human visual cortex. The typical hemodynamic changes expected were observed; the total-Hb and oxy-Hb increased just after the start of stimulation and plateaued after 10 s of the stimulation period.

Adult↗
PubMedDate not supplied

[Dynamics of evoked responses in the visual cortex of intact and callosotomized cats to visual stimuli of different intensity].

The comparison of histograms of distribution of monocular and binocular EPs amplitudes in the striate and parastriate cortex of intact and callosectomized cats with the corresponding histograms of intensities of random light flashes revealed a transformation of stimuli distribution function. In intact animals, EPs distribution was characterized by a left-side asymmetry and predominance of mean-amplitude EPs. It is suggested that the above distribution characteristics reflect the principle of optimization. Its presence as well as characteristics of its manifestation in definite visual areas and with different types of stimuli lateralization are largely due to transcallosal influences modulating the value and power spectrum of thalamocortical excitation.

Animals↗
PubMed1993

Autoradiographic localization of serotonin receptor subtypes in cat visual cortex: transient regional, laminar, and columnar distributions during postnatal development.

Postnatal changes in the distribution of 5-HT receptor subtypes in the visual cortex of cats were assessed both qualitatively and quantitatively using in vitro autoradiographic methods. The 5-HT 1A, 1C, 2, and 3 receptor subtypes and the 5-HT uptake (5-HTUp) site were visualized with 3H-8-hydroxy-2(di-n-propyl-amino)tetralin, 3H-mesulergine, (2,5-dimethoxy-4-125I-iodophenyl)-2-aminopropane, 3H-BRL43694, and 3H-cyanoimipramine, respectively. Although specific labeling of 5-HT3 receptors was not detected in the cat visual cortex at any age, each of the remaining 5-HT receptor subtypes exhibited unique temporal, regional, and laminar patterns of expression in visual cortical areas 17, 18, and 19 and lateral suprasylvian cortex (LS). 5-HT1A receptors were the earliest to demonstrate visual cortex-specific changes in expression. They exhibited peak levels of expression in all visual cortical areas, predominantly in supra- and infragranular layers, between postnatal day 10 (PD10) and PD30. Their levels in all areas declined progressively with increasing age. 5-HT1c receptors demonstrated their highest levels of expression in the deeper half of layer IV, but only in area 17, between PD40 and PD75. The most striking feature of their distribution throughout this period was that, in layer IV and extending into layer III, the 5-HT1c receptors were concentrated in columns that were 400 microns wide and had a center-to-center spacing of about 900 microns. This transient pattern of expression was not present beyond PD90. 5-HT2 receptors were most densely expressed in layer IV between PD40 and PD120, but they displayed a distinctly different distribution pattern. The densest binding of 5-HT2 receptors was limited to the upper half of layer IV and found in areas 17, 18, and LS. The distribution of layer 5-HT2 receptors along the dense band in layer IV of area 17 was discontinuous, exhibiting patches that were found in the same vertical columns as were the 5-HT1c receptors. Intermediate binding levels for the 5-HT2 receptors were found through layers I-III, the remainder of layer IV, and the subcortical white matter. The levels of 5-HT uptake sites increased gradually to reach adult levels by PD40, but with a distribution pattern that was basically homogeneous, both across cortical regions and across laminae.(ABSTRACT TRUNCATED AT 400 WORDS)

8-Hydroxy-2-(di-n-propylamino)tetralin↗