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PubMed1998

Visual evoked cortical magnetic responses to checkerboard pattern reversal stimulation: a study on the neural generators of N75, P100 and N145.

In an attempt to elucidate the neural generators of pattern reversal visual evoked potentials (PR-VEPs), we measured the visual evoked magnetic fields (PR-VEFs) using a 37-channel magnetoencephalography in six healthy young adults. A half-field checkerboard pattern was phase-reversed at a rate of 1 Hz to stimulate the right or left visual half-field, thus yielding 12 PR-VEFs in total from the six subjects. The simultaneously recorded scalp PR-VEPs showed three distinct components of N75, P100 and N145. Three corresponding components were also identified in the PR-VEFs with similar peak latencies (N75m, P100m and N145m). P100m and N145m were clearly identified in all 12 PR-VEFs, whereas N75m was observed in only nine of 12 PR-VEFs. The equivalent current dipoles (ECDs) of N75m, P100m and N145m were located closely to each other in the occipital cortex around the calcarine fissure contralateral to the stimulated visual field, when they were overlaid on the MRI. The reliability of dipole estimation was highest in P100m, followed by N145m while N75m showed the least reliability. The direction of the current flow of ECDs of N75m and N145m was from the medial to the lateral in the occipital cortex when viewed in a coronal section, whereas that for P100m was toward the medial. The ECD location of P100m changed according to the retinotopic organization when the upper or lower quadrant of the visual field was stimulated, with the ECDs being located in the lower or upper part, respectively, of the visual cortex. Our results therefore indicate that the neural origins of N75m, P100m and N145m of PR-VEFs are in the primary visual cortex on the contralateral side of the stimulated visual half-field, while the three components are physiologically distinct.

Adult↗
PubMed1986

Quantitative distribution of GABA-immunoreactive neurons in the visual cortex (area 17) of the cat.

Cortical neurons using the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) are known to contribute to the formation of neuronal receptive field properties in the primary visual cortex (area 17) of the cat. In order to determine the cortical location of GABA containing neurons and what proportion of cortical neurons might use GABA as their transmitter, we analysed their distribution quantitatively using a post-embedding GABA immunohistochemical method on semithin sections in conjunction with stereological procedures. The mean total numerical density of neurons in the medial bank of the lateral gyrus (area 17) of five adult cats was 54,210 +/- 634 per mm3 (mean +/- SD). An average of 20.60 +/- 0.48% (mean +/- SEM) of the neurons were immunoreactive for GABA. The density of GABA-immunoreactive neurons was somewhat higher in layers II, III and upper VI, compared with layers I, IV, V and lower VI, with the lowest density being in layer V. The proportion of GABA-immunopositive cells relative to immunonegative neurons gradually decreased from the pia to the white matter. Layer I was different from other layers in that approximately 95% of its neurons were GABA-immunoreactive. The results allowed the calculation of the absolute numbers of GABAergic neurons in each layer under a given cortical surface area and could provide the basis for the quantitative treatment of cortical circuits.

Animals↗
PubMed2006

L-arginine treatment early in life influences NADPH-diaphorase neurons in visual cortex of normal and early-malnourished adult rats.

This study investigated the effects of repeated l-arginine administration during lactation, combined with different suckling conditions, on morphometric parameters of primary visual cortex NADPH-diaphorase-positive neurons. Wistar rat pups reared in "normal-size litters" or "large litters" (N- and L-conditions; litters formed by 6 and 12 pups, respectively) received, from postnatal day 7 to 28, either arginine (300 mg/kg/day, per gavage) or distilled water (control). At 90-120 days of life, they were perfused with saline + formaldehyde, and their brains were processed for histochemical reaction to reveal NADPH-diaphorase-positive neurons (malic enzyme indirect method). Compared to the normal-size litters, L-rats had lower body weights (P < 0.05), confirming the effectiveness of the L-condition in affecting pup development. Concerning NADPH-d histochemistry, arginine treatment was associated with increased (P < 0.05) density of dendrite varicosities and of dendrite branching frequency, suggesting a plastic response of the developing brain to that treatment, even in previously malnourished rats. No difference was seen, however, in dendrite orientation, total number of neurons, soma area and perimeter, as well as dendrite bifurcation points, fractal dimension, and area and volume of dendrite field, suggesting that NADPH-d cells are resistant to arginine and nutritional changes, regarding these features. Data are considered of interest for studies of synaptic plasticity during neural development and its relationships to aggressive agents like malnutrition.

Animals↗
PubMedDate not supplied

States of high conductance in a large-scale model of the visual cortex.

This paper reports on the consequences of large, activity dependent, synaptic conductances for neurons in a large-scale neuronal network model of the input layer 4Calpha of the Macaque primary visual cortex (Area V1). This high conductance state accounts for experimental observations about orientation selectivity, dynamics, and response magnitude (D. McLaughlin et al. (2000) Proc. Natl. Acad. Sci. USA 97: 8087-8092), and the linear dependence of Simple cells on visual stimuli (J. Wielaard et al. (2001) J. Neuroscience 21: 5203-5211). The source of large conductances in the model can be traced to inhibitory corticocortical synapses, and the model's predictions of large conductance changes are consistent with recent intracellular measurements (L. Borg-Graham et al. (1998) Nature 393: 369-373; J. Hirsch et al. (1998) J. Neuroscience 15: 9517-9528; J.S. Anderson et al. (2000) J. Neurophysiol. 84: 909-926). During visual stimulation, these conductances are large enough that their associated time-scales become the shortest in the model cortex, even below that of synaptic interactions. One consequence of this activity driven separation of time-scales is that a neuron responds very quickly to temporal changes in its synaptic drive, with its intracellular membrane potential tracking closely an effective reversal potential composed of the instantaneous synaptic inputs. From the effective potential and large synaptic conductance, the spiking activity of a cell can be expressed in an interesting and simplified manner, with the result suggesting how accurate and smoothly graded responses are achieved in the model network. Further, since neurons in this high-conductance state respond quickly, they are also good candidates as coincidence detectors and burst transmitters.

Animals↗
PubMedDate not supplied

[Dynamics of tuning to orientation of cross-like figures in neurons from the cat visual cortex].

Dynamics of tuning to orientation of flashing light bar and to orientation of cross-like figure was studied by a temporal slices method in 87 neurons of the cat primary visual cortex. Tuning was plotted by spikes number in the entire response and in its successive fragments with a step of 20 ms. It was found that successive dynamic shift of preferred orientation of a bar was typical for 87% units, white such shift of preferred orientation of a cross was met in 75% of cases. Comparison of tuning dynamics for bar and cross allowed to separate units into three groups: the first one (58.6% of cases) with larger dynamic shift of a bar preferred orientation then of a cross (74.9 +/- 5.8 degrees [symbol: see text] 29.8 +/- 4.1 degrees, correspondingly, p < 0.00001), the second group (21.5%) with opposite effect (24.2 +/- 5.2 degrees and 69.2 +/- 10.0 degrees, p < 0.0002) and the third group (19.8%) without significant shift of preferred orientation of bar and cross and without difference in their dynamics. Possible mechanisms of the preferred orientation dynamics and its difference for bar and cross are discussed.

Action Potentials↗
PubMed2006

Physiological and anatomical evidence for multisensory interactions in auditory cortex.

Recent studies, conducted almost exclusively in primates, have shown that several cortical areas usually associated with modality-specific sensory processing are subject to influences from other senses. Here we demonstrate using single-unit recordings and estimates of mutual information that visual stimuli can influence the activity of units in the auditory cortex of anesthetized ferrets. In many cases, these units were also acoustically responsive and frequently transmitted more information in their spike discharge patterns in response to paired visual-auditory stimulation than when either modality was presented by itself. For each stimulus, this information was conveyed by a combination of spike count and spike timing. Even in primary auditory areas (primary auditory cortex [A1] and anterior auditory field [AAF]), approximately 15% of recorded units were found to have nonauditory input. This proportion increased in the higher level fields that lie ventral to A1/AAF and was highest in the anterior ventral field, where nearly 50% of the units were found to be responsive to visual stimuli only and a further quarter to both visual and auditory stimuli. Within each field, the pure-tone response properties of neurons sensitive to visual stimuli did not differ in any systematic way from those of visually unresponsive neurons. Neural tracer injections revealed direct inputs from visual cortex into auditory cortex, indicating a potential source of origin for the visual responses. Primary visual cortex projects sparsely to A1, whereas higher visual areas innervate auditory areas in a field-specific manner. These data indicate that multisensory convergence and integration are features common to all auditory cortical areas but are especially prevalent in higher areas.

Acoustic Stimulation↗
PubMed2001

Building surfaces from borders in Areas 17 and 18 of the cat.

Several brightness illusions indicate that borders can dramatically affect the perception of adjoining surfaces. In the Craik-O'Brien-Cornsweet illusion, in particular, two equiluminant surfaces can appear different in brightness due to the contrast border between them. Although the psychophysical nature of this phenomenon has been well characterized, the neural circuitry underlying this effect is unexplored. Here, we have asked whether there are cells in visual cortex which respond to edge-induced illusory brightness percepts such as the Cornsweet. Using optical imaging and single unit recordings methods, we have studied responses of the primary (Area 17) and second (Area 18) visual cortical areas of the anesthetized cat to both real luminance change and Cornsweet brightness change. We find that there are indeed cells whose responses are modulated in phase with the modulation of the Cornsweet stimulus. These cells are present in both Area 17 and Area 18, but are more prevalent in Area 18. These responses are generally weak and are found even when receptive fields are distant from the contrast border. Consistent with perception, cells which respond to the Cornsweet border are modulated in antiphase to the Narrow Real (another border-induced illusory brightness stimulus). Remarkably, we also find evidence of edge-induced responses to illusory brightness change using intrinsic signal optical imaging. Both real luminance change and edge-induced brightness change produces a greater imaged response in Area 18 than in Area 17. Thus, in the absence of direct luminance stimulation, cells in visual cortex can respond to modulation of distant border contrasts. We suggest that the perception of surface brightness was encoded in the early visual cortical pathway by both surface luminance contrast signals in Area 17 (Rossi, A. F., Rittenhouse, C. D., & Paradiso, M. A. (1996). The representation of brightness in primary visual cortex. Science, 273, 1104-7) and border-induced contrast signals that predominate in Area 18.

Animals↗
PubMedDate not supplied

[An analysis of interhemispheric interrelationships in the visual cortex of cats based on the law of contrast perception of light].

The dependence of EP amplitude on the intensity of photic stimuli before and after section of the callosal body may be fully defined by the equation of the contrast law of light perception. Analysis of the nature of interhemispheric relationships by means of contrast law has shown that both reciprocal depressing and reciprocal facilitating interhemispheric relationships may exist in the primary visual cortical projection zone, and reciprocal facilitating interhemispheric influences in the secondary visual projection zone. Similarity of interhemispheric relationships has been recorded in the primary visual cortex in cats and in the secondary one, in rats, as well as in the socondary visual cortical zone in cats, and in the primary, in rats. Interhemispheric reciprocal influences in the whole range of stimuli intensities are distributed more uniformly in cats than in rats. Cats may perceive a wider range of intensity of photic stimuli than rats. In cats as in rats, the effectiveness of processing of the photic stimuli contrast is greater in the secondary visual cortical projection zone than in the primary one.

Animals↗
PubMed1995

Retinal detachment induces massive immediate reorganization in visual cortex.

Large inactive regions of the retina of adult cats were produced by the novel method of inducing monocular retinal detachment. Within a few hours, neurones throughout the detachment projection zone in primary visual cortex (55-136 mm2), including some > 4.5 mm from its boundary, were found to have large receptive fields displaced onto intact retina. The new receptive fields of some neurones represented shifts of up to 9 mm across the retinotopic representation. For these rapid changes to occur pre-existing viable circuits must provide a cortical locus with inputs from a wide extent of the retina. Receptive fields, and the retinotopic map, for stimulation of the other eye were unchanged.

Animals↗
PubMed1997

Modulation of intrinsic circuits by serotonin 5-HT3 receptors in developing ferret visual cortex.

Serotonergic projections are widespread in the developing neocortex, but their functions are obscure. The effects of 5-HT3 receptor agonists on cortical circuit response properties were studied in slices of ferret primary visual cortex using high-speed optical imaging of voltage-sensitive dye signals and whole-cell patch-clamp recording. Activation of the 5-HT3 receptor decreased the amplitude and lateral extent of excitation throughout postnatal development. This effect peaks after eye opening, which indicates a function for serotonergic modulation of circuit responses during the period of refinement of cortical connections. Whole-cell patch-clamp recordings from single neurons revealed that synaptic responses evoked by white matter stimulation were reduced by 5-HT3 receptor agonists, whereas the frequency of spontaneous GABAergic synaptic currents was enhanced dramatically. This indicates that the modulation of spontaneous synaptic activity by fast-acting serotonin receptors is reflected in an inhibition of the circuit response, in line with the notion of background synaptic activity altering the spatiotemporal integration properties of cortical cells by changing their membrane potential and their electrotonic structure. These mechanisms may regulate the response properties of intrinsic circuits in both the adult and developing neocortex.

2-Amino-5-phosphonovalerate↗
PubMed2001

Modular organization of intrinsic connections associated with spectral tuning in cat auditory cortex.

Many response properties in primary auditory cortex (AI) are segregated spatially and organized topographically as those in primary visual cortex. Intensive study has not revealed an intrinsic, anatomical organizing principle related to an AI functional topography. We used retrograde anatomic tracing and topographic physiologic mapping of acoustic response properties to reveal long-range (> or = 1.5 mm) convergent intrinsic horizontal connections between AI subregions with similar bandwidth and characteristic frequency selectivity. This suggests a modular organization for processing spectral bandwidth in AI.

Animals↗
PubMed2004

Exclusive postsynaptic action of hypocretin-orexin on sublayer 6b cortical neurons.

The hypocretin-orexin (hcrt-orx) neurons are thought to maintain wakefulness because their loss results in narcolepsy. This role may be fulfilled by the excitatory action that the hcrt-orx peptide exerts on multiple brainstem and forebrain systems that, in turn, promote cortical activation. Here, we examined whether hcrt-orx may also exert a postsynaptic excitatory action at the level of the cortex, where hcrt-orx fibers project. However, we found that neurons in layers 2-5 in the primary somatosensory cortex (SSp) were unresponsive to hcrt-orx. We then found that although all neurons tested in sublayer 6a were also unresponsive to hcrt-oxr, all those tested in sublayer 6b were highly sensitive to the peptide. The sublayer selectivity of hcrt-oxr was not restricted to the somatosensory cortex, because it was also found to be present in the primary visual cortex, the motor cortex, and the cingulate cortex. In the SSp, in which the hcrt-oxr effect was investigated further, it was demonstrated to be postsynaptic, to result from an interaction with Hcrtr2-OX2 receptors and to depend on the closure of a potassium conductance. Similar to the selectivity of action in the thalamus, where hcrt-oxr excites the nonspecific thalamocortical projection neurons and not the specific sensory relay neurons, here in the cortex, it excites a specific subset of cortical neurons which, through corticocortical projections, may also be involved in promoting widespread cortical activation.

Animals↗
PubMed1998

Nitric oxide synthase and the acetylcholine receptor in the prefrontal cortex: metasynaptic organization of the brain.

Nitric oxide synthase (NOS) and the nicotinic acetylcholine receptor (nAChR) immunoreactivity of the cerebral cortex was studied in adult Macaca fascicularis monkeys at light- and electron microscopic levels. NOS was located by means of the polyclonal antibodies developed by Transduction Laboratories (Lexington, KY, USA), as primary serum, in a dilution of 1:1000, and nAChR was located by means of biotinylated alpha-bungarotoxin (BTX) obtained from Molecular probes (Eugene, Oregon, USA) in a dilution of 1:2000. While endothelial eNOS outlined blood vessels in the brain, brain-derived (neural) bNOS labelled three well-defined cell types in area 46 of the prefrontal cortex, viz. (a) bipolar cells, scattered through layers III to V, equipped with long dendrites which pass over the thickness of the cortex in a right angle to the pial surface, establishing dendritic bundles closely reminiscent of a columnar organization; (b) large multipolar cells, located mainly in layers V and VI, with axons which interconnect dendritic bundles of the bipolar cells and establish synapses with dendritic shafts and spines of the former; and (c) stellate cells, located in lamina II and III, which establish an axonal network in lamina zonalis (lamina I). This arrangement is most characteristic in area 46 of the prefrontal cortex; areas 10 and 12 display similar features. In contrast, the primary visual cortex (area 17), is lacking any sign of columnar organization. Localization of bNOS immunoreactivity is at marked variance to that of NADPH-diaphorase which labels large pyramidal cells in the primate cortex. Binding of alpha-bungarotoxin (BTX) which labels the alpha 7 subunit of nAChR is located in somata, dendrites and axons of interneurons scattered over the entire width of the prefrontal cortex; on the other hand, the monoclonal antibody mAb 35 which labels subunits alpha 1, alpha 3 and alpha 5 in the main immunogenic region of the receptor, visualizes apical dendritic shafts similar to those like bNOS. Strategic localization of bNOS in the primate prefrontal cortex fulfills criteria of producing a freely diffusing retrograde messenger molecule operative in signal transduction routes subserving topography and columnar organization of the cortex, as well as long-term potentiation and long-term depression phenomena underlying mnemonic and gnostic functions. Common occurrence of bNOS and nAChR in identical or similar structures in the prefrontal cortex suggests that interactions between nitrogen oxide and presynaptically released acetylcholine might be involved in the metasynaptic organization of the cerebral cortex, operating in a non-synaptic manner in maintaining optimal performance on cognitive tasks.

Animals↗
PubMed1983

Immunohistochemical demonstration of serotonin nerve fibers in the neocortex of the monkey (Macaca fuscata).

Using a peroxidase-antiperoxidase immunohistochemical method, the distribution of serotonin nerve fibers was studied in the neocortex of the monkey (Macaca fuscata). All layers of the neocortex showed evidence of serotonin fibers, both fine and thick. Unlike the distribution in rodents, different patterns of distribution were noted in each neocortex of the primate. Among the cortical areas--area 4, 3-1-2, 17, 18, 41 and 42--the primary visual cortex (area 17) contained the highest density of immunoreactive fibers, while the primary motor cortex (area 4) possessed the lowest concentration. The most outstanding finding was a dense and laminar distribution of serotonin fibers in area 17, particularly within the upper portion of layer IVc. In area 3-1-2, 18, 41 and 42, a fairly uniform density of immunoreactive fibers was observed across the six cortical layers, apart from a relatively dense plexus of fine serotonin fibers in layer IV.

Animals↗
PubMed1981

Stroboscopic rearing reduces direction selectivity in rabbit visual cortex.

Rabbits reared from birth in stroboscopic illumination have no experience of visual motion. In primary visual cortex of these animals there is a large reduction in the number of cells which are direction selective. This result, contrary to previous reports, shows that the rabbit visual system can be modified by early visual experience.

Animals↗
PubMed1985

Topography of cytochrome oxidase activity in owl monkey cortex.

In primate cortical tissue which has been stained for the mitochondrial enzyme cytochrome oxidase, a topographical pattern of regularly spaced blobs has been demonstrated in primary visual cortex (Hendrickson, A. E., S. P. Hunt, and J. -Y. Wu (1981) Nature 292: 605-607; Horton, J. C., and D. H. Hubel (1981) Nature 292: 762-764), and a pattern of stripes has been shown in secondary visual cortex (V2) as well (Livingstone, M. S., and D. H. Hubel (1982) Proc. Natl. Acad. Sci. U. S. A. 79: 6098-6101; Tootell, R. B. H., M. S. Silverman, E. Switkes, and R. L. De Valois (1982) Soc. Neurosci. Abstr. 8: 707). These regular cytoarchitectonic landmarks have proven extremely useful in parsing the functional and anatomical architecture of these two cortical areas. In order to look for similar landmarks in other cortical areas of a primate, we completely unfolded the cortical gray matter in the owl monkey (Aotus trivirgatus), sectioned it parallel with the flattened cortical surface, and stained the tissue for cytochrome oxidase. Distinctive cytochrome oxidase topographies were found in about seven different cortical areas. As in other primates, area V1 is characterized by blobs and area V2 is characterized by strips. In the owl monkey, area MT is characterized by an elaborate topography of dark staining in layers 1 to 4, interspersed with light blob-shaped regions, and partially surrounded by a dark ring. Many of these topographic inhomogeneities are also reflected in the lower layer myelination topography in MT. Visual area(s) VP/VA is characterized by an irregular or strip-like topography. In some animals, a distinctive topography can be seen in area DX, which is presumably equivalent to either area DM or DI. Primary auditory cortex stains very darkly, but the overall shape of area A is quite variable and the borders are indistinct. Somatosensory area 3B stains quite darkly with sharp borders, but again the overall shape of area 3B is different from that previously described.

Animals↗
PubMed1993

Modification in primary visual cortical activity of rat induced by neonatal monocular enucleation, an electrophysiological and autoradiographic study.

Mononuclear enucleation was performed in rats at birth. The animals were raised and from the age of 3 months the evoked activity was tested in the contralateral visual cortex both by mapping of evoked potentials and autoradiography. It was found that monocular enucleation changed the distribution of evoked activity characteristically. The focus of activity shifted laterally and restricted itself to the binocular part of the primary visual cortex (Oc1B), while, in the medial part of it (Oc1M) hardly any evoked activity or labelled neurons were found

Animals↗
PubMed1995

Direct visual pathways for reaching movements in the macaque monkey.

The brain seems to process the location of objects faster than their intrinsic features, such as size, when these parameters are used to guide action. To uncover a potential anatomical substrate of these different processing speeds, we investigated in the monkey the pathways linking extrastriate visual cortex with the dorsal premotor area, a frontal area known to be involved in visually guided reaching movements. Retrogradely transported anatomical tracers were injected at physiologically defined sites and the distribution of labelled cells was examined in the ipsilateral cortex. We found a projection to the dorsal premotor cortex from the parieto-occipital area (PO). This area receives direct projections from the primary visual cortex (V1), and is part of the dorsal visual stream involved in the processing of spatial information. No direct projections to the dorsal premotor cortex arise from the ventral visual areas, thought to process object features. Our finding provides evidence for direct pathways from the dorsal visual stream to the dorsal premotor cortex and supports the view that the location of objects is processed faster by the brain than their intrinsic features.

Animals↗