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PubMed1994

A neurochemically distinct third channel in the macaque dorsal lateral geniculate nucleus.

The primate visual system is often divided into two channels, designated M and P, whose signals are relayed to the cerebral cortex by neurons in the magnocellular and parvicellular layers of the dorsal lateral geniculate nucleus. We have identified a third population of geniculocortical neurons in the dorsal lateral geniculate nucleus of macaques, which is immunoreactive for the alpha subunit of type II calmodulin-dependent protein kinase. This large third population occupies interlaminar regions (intercalated layers) ventral to each principal layer. Retrograde labeling of kinase-immunoreactive cells from the primary visual cortex shows that they provide the geniculocortical input to cytochrome oxidase-rich puffs in layers II and III.

Animals↗
PubMed1996

Functional mapping of color processing by magnetic resonance imaging of responses to selective P- and M-pathway stimulation.

Magnetic resonance imaging sensitized to activity-related changes in cerebral blood oxygenation was performed to map responses to selective stimulation of the parvo- and magnocellular visual pathways in calcarine and adjacent ventral occipital cortex of human subjects. In a repetitive stimulation protocol isoluminant chromatic or isochromatic luminance modulation was alternated with steady light of the same mean chromaticity and luminance as a reference condition. While no significant effects were observed for diffuse luminance modulation, two consistent cortical foci responded to isoluminant chromatic stimulation. A strong response was obtained in calcarine cortex at both 2 and 10 Hz, and even for selective S-cone stimulation. A second weaker color-sensitive response was seen bilaterally in the collateral sulcus. Thus, the data not only confirm color-sensitive activation in the collateral sulcus elicited in previous studies by selective cognitive tasks, but additionally demonstrate color-sensitive activation in primary visual cortex. With stimuli defined according to electrophysiological response properties of early visual processing stages, this study complements phenomenological or cognitive approaches in functional mapping of the human visual system.

Adult↗
PubMed1993

Visual deprivation decreases long-term potentiation in rat visual cortical slices.

A major finding in the visual plasticity literature is that visual deprivation is effective only during an early 'sensitive' period, which is lengthened by dark rearing. Unresolved is whether the visual cortex is in a normally plastic state prior to light stimulation. This cannot be addressed using paradigms employing light exposure to assess plasticity. Several developmental studies have investigated a plastic phenomenon termed long-term potentiation (LTP) in slices from cat (J. Neurophysiol., 59 (1988) 124-141) and rat (Brain Res., 439 (1988) 222-229) visual cortex. Susceptibility to the induction of LTP parallels the period of sensitivity to visual deprivation. This suggests that slices can be used to assay visual cortical plasticity, avoiding light exposure. In the present study, field potentials were recorded from slices of the primary visual cortices of dark-reared (DR) and control (CONT) Long Evans hooded rats (17 to 21 days). Field potential profiles recorded before and 90 min following tetanic electrical stimulation were subjected to current source density analysis, yielding extracellular current sink amplitudes. Tetanus resulted in LTP in both CONT and DR slices, but DR slices were significantly less potentiated. These results indicate that the primary visual cortex of DR animals is not fully plastic, indicating a role for light stimulation in inducing visual cortical plasticity.

Animals↗
PubMed2005

Visibility reflects dynamic changes of effective connectivity between V1 and fusiform cortex.

Identifying the neural basis of visibility is central to understanding conscious visual perception. Visibility of basic features such as brightness is often thought to reflect activity in just early visual cortex. But here we show under metacontrast masking that fMRI activity in stimulus-driven areas of early visual cortex did not reflect parametric changes in the visibility of a brightness stimulus. The psychometric visibility function was instead correlated with activity in later visual regions plus parieto-frontal areas, and surprisingly, in representations of the unstimulated stimulus surround for primary visual cortex. Critically, decreased stimulus visibility was associated with a regionally-specific decoupling between early visual cortex and higher visual areas. This provides evidence that dynamic changes in effective connectivity can closely reflect visual perception.

Adult↗
PubMed1998

Hippocampal and cortical growth-associated protein-43 messenger RNA in schizophrenia.

Growth-associated protein-43 is involved in maturational and plasticity-associated processes, and changes in growth-associated protein-43 expression are a marker of altered plasticity following experimental and neuropathological lesions. Using in situ hybridization, we have investigated growth-associated protein-43 mRNA in the medial temporal lobe and cerebral cortex in 11 normal subjects and 11 matched subjects with schizophrenia, a disorder in which perturbed neurodevelopment and aberrant plasticity are implicated. In the schizophrenia group, growth-associated protein-43 messenger RNA was decreased in the medial temporal lobe, primary visual cortex and anterior cingulate gyrus, but was unaltered in the superior temporal and dorsolateral prefrontal cortices. Correlations of growth-associated protein-43 messenger RNA signal between areas were stronger and more numerous in the schizophrenics than in the controls, suggesting a more global regulation of growth-associated protein-43 expression. Finally, the ratio of growth-associated protein-43 messenger RNA to synaptophysin messenger RNA--a putative index of the production of new synapses--was decreased in the medial temporal lobe in the schizophrenics. Our findings imply that neuronal plasticity as indexed by growth-associated protein-43 expression is impaired, and perhaps aberrantly regulated, in schizophrenia. The data support the emerging view that the disease pathophysiology is one which affects the hippocampal and cortical circuitry and that the abnormalities are reflected in the altered expression of specific neuronal genes.

Adult↗
PubMed2005

Tilt aftereffect and adaptation-induced changes in orientation tuning in visual cortex.

The tilt aftereffect (TAE) is a visual illusion in which prolonged adaptation to an oriented stimulus causes shifts in subsequent perceived orientations. Historically, neural models of the TAE have explained it as the outcome of response suppression of neurons tuned to the adapting orientation. Recent physiological studies of neurons in primary visual cortex (V1) have confirmed that such response suppression exists. However, it was also found that the preferred orientations of neurons shift away from the adapting orientation. Here we show that adding this second factor to a population coding model of V1 improves the correspondence between neurophysiological data and TAE measurements. According to our model, the shifts in preferred orientation have the opposite effect as response suppression, reducing the magnitude of the TAE.

Adaptation, Physiological↗
PubMed2000

[Disinhibition as a mechanism of tuning of cross-like figures in the visual cortex neurons].

A discrete neural net was used for simulation of cross-sensitivity in 40% of neurones of the cat visual cortex' area 17th. It is based on disinhibition of the end-stopping inhibition in receptive field from the side-disinhibitory zone. Highly selective or invariant sensitivity of the simulated neurone in respect to shape and orientation of a cross-like figure was observed under changes of location, size and weight of the receptive field zones. The disinhibitory mechanism seems to be critically involved in the selection of the second-order features of the images in the primary visual cortex.

Animals↗
PubMed1999

Effect of the group II metabotropic glutamate agonist, 2R,4R-APDC, varies with age, layer, and visual experience in the visual cortex.

Group II metabotropic glutamate receptors (mGluR 2/3) are distributed differentially across the layers of cat visual cortex, and this distribution varies with age. At 3-4 wk, mGluR 2/3 receptor immunoreactivity is present in all layers. By 6-8 wk of age, it is still present in extragranular layers (2, 3, 5, and 6) but has disappeared from layer 4, and dark-rearing postpones the disappearance of Group II receptors from layer 4. We examined the physiological effects of Group II activation, to see if these effects varied similarly. The responses of single neurons in cat primary visual cortex were recorded to visual stimulation, then the effect of iontophoresis of 2R,4R-4 aminopyrrolidine-2, 4-decarboxylate (2R,4R-APDC), a Group II specific agonist, was observed in animals between 3 wk and adulthood. The effect of 2R, 4R-APDC was generally suppressive, reducing both the visual response and spontaneous activity of single neurons. The developmental changes were in agreement with the immunohistochemical results: 2R, 4R-APDC had effects on cells in all layers in animals of 3-4 wk but not in layer 4 of animals >6 wk old. Moreover, the effect of 2R, 4R-APDC was reduced in the cortex of older animals (>22 wk). Dark-rearing animals to 47-54 days maintained the effects of 2R, 4R-APDC in layer 4. The disappearance of Group II mGluRs from layer 4 between 3 and 6 wk of age is correlated with the segregation of ocular dominance columns in that layer, raising the possibility that mGluRs 2/3 are involved in this process.

Aging↗
PubMed2003

Features of neuronal synchrony in mouse visual cortex.

Synchronization of neuronal discharges has been hypothesized to play a role in defining cell assemblies representing particular constellations of stimulus features. In many systems and species, synchronization is accompanied by an oscillatory response modulation at frequencies in the gamma-band. The cellular mechanisms underlying these phenomena of synchronization and oscillatory patterning have been studied mainly in vitro due to the difficulty in designing a direct in vivo assay. With the prospect of using conditional genetic manipulations of cortical network components, our objective was to test whether the mouse would meet the criteria to provide a model system for the study of gamma-band synchrony. Multi-unit and local field potential recordings were made from the primary visual cortex of anesthetized C57BL/6J mice. Neuronal responses evoked by moving gratings, bars, and random dot patterns were analyzed with respect to neuronal synchrony and temporal patterning. Oscillations at gamma-frequencies were readily evoked with all types of stimuli used. Oscillation and synchronization strength were largest for gratings and decreased when the noise level was increased in random-dot patterns. The center peak width of cross-correlograms was smallest for bars and increased with noise, yielding a significant difference between coherent random dot patterns versus patterns with 70% noise. Field potential analysis typically revealed increases of power in the gamma-band during response periods. Our findings are compatible with a role for neuronal synchrony in mediating perceptual binding and suggest the usefulness of the mouse model for testing hypotheses concerning both the mechanisms and the functional role of temporal patterning.

Action Potentials↗
PubMed1987

Ectosylvian visual area of the cat: location, retinotopic organization, and connections.

We have mapped out the ectosylvian visual area (EVA) of the cat in a series of single- and multiunit recording studies. EVA occupies 10-20 mm2 of cortex at the posterior end of the horizontal limb of the anterior ectosylvian sulcus. EVA borders on somatosensory cortex anteriorly, auditory cortex posteriorly, and nonresponsive cortex laterally. EVA exhibits limited retinotopic organization, as indicated by the fact that receptive fields shift gradually with tangential travel of the microelectrode through cortex. However, a point-to-point representation of the complete visual hemifield is not present. We have characterized the afferent and efferent connections of EVA by placing retrograde and anterograde tracer deposits in EVA and in other cortical visual areas. The strongest transcortical fiber projection to EVA arises in the lateral suprasylvian visual areas. Area 20, the granular insula, and perirhinal cortex provide additional sparse afferents. The projection from lateral suprasylvian cortex to EVA arises predominantly in layer 3 and terminates in layer 4. EVA projects reciprocally to all cortical areas from which it receives input. The projection from EVA to the lateral suprasylvian areas arises predominantly in layers 5 and 6 and terminates in layer 1. EVA is linked reciprocally to a thalamic zone encompassing the lateromedial-suprageniculate complex and the adjacent medial subdivision of the latero-posterior nucleus. We conclude that EVA is an exclusively visual area confined to the anterior ectosylvian sulcus and bounded by nonvisual cortex. EVA is distinguished from other visual areas by its physical isolation from those areas, by its lack of consistent global retinotopic organization, and by its placement at the end of a chain of areas through which information flows outward from the primary visual cortex.

Animals↗
PubMedDate not supplied

A grading system of Alzheimer disease lesions in neocortical areas.

Progression of neuritic and Abeta pathology in the cerebral cortex during aging and Alzheimer disease is well known, but the chronology of the various types of lesions (Abeta deposition, amyloid formation, inflammation, ubiquitination, tangle formation) within a given area has not been fully elucidated. We examined these lesions in the primary visual cortex (Brodmann area 17), correlating them with the severity of the disease (as evaluated by the cognitive status and the number of cortical samples that contained neurofibrillary tangles). Four 'grades' were identified. At grade 1, only deposits of Abeta peptide were noticed. At grade 2, Congo red positive deposits, and processes containing ubiquitin and cathepsin D immunoreactivity around plaque cores could also be found. At grade 3, neuritic plaques and neuropil threads were present, and at grade 4, neurofibrillary tangles. The density of all the lesions dramatically increased at grade 4. The sequence of isocortical lesions from grade 1 to grade 4 is compatible with a cascade of events beginning with deposition of Abeta peptide and ending with neurofibrillary tangle.

Aged↗
PubMed2001

Functional magnetic resonance imaging of odor identification: the effect of aging.

BACKGROUND: Sense of smell declines with age and impairment in olfaction has been observed in some neurodegenerative disorders such as Alzheimer's disease. Functional neuroimaging techniques enable researchers to observe brain regions activated by olfactory stimuli. METHODS: We gave three mainly olfactory-mediated odors (limonene, methylsalicylate, and eugenol) to six young and six elderly subjects and observed the areas activated by using blood oxygen level dependent contrast functional magnetic resonance imaging. RESULTS: The group mapping of young subjects showed extensive activation in the orbitofrontal cortex, commonly believed to be the olfactory cortex, some limbic areas (the hippocampus and the thalamus), regions involved with gustatory sensation (the anterior insula and the inferior postcentral gyrus), superior and inferior temporal gyri, and cerebellum. In the elderly group, only the left inferior temporal gyrus and the primary visual cortex reached accepted significance levels. CONCLUSIONS: We have therefore confirmed previous reports of brain regions involved in olfactory processing in young volunteers and demonstrated decreased activation in elderly volunteers.

Adult↗
PubMed2000

A new cat Fos antibody to localize the immediate early gene c-fos in mammalian visual cortex after sensory stimulation.

We developed a novel antibody against cat Fos by immunizing rabbits with a 26-amino-acid peptide. Immunocytochemistry on visual cortex of cats undergoing different visual manipulations was applied to test the reliability and the efficacy of this antiserum. One hour of light stimulation after an overnight dark adaptation resulted in strongly induced Fos expression in supra- and infragranular layers of cat primary visual cortex. Short-term monocular deprivation changed the Fos expression profile into a columnar immunostaining related to ocular dominance columns. Fos expression has also been analyzed in cats in which visual input was confined to the right hemisphere by sectioning the left optic tract and the corpus callosum. In the right hemisphere, visual stimulation elicited Fos induction, whereas in the contralateral hemisphere a very low Fos signal was observed. The specificity of this newly synthesized antibody was confirmed by Western blotting. To further establish the applicability of this Fos antiserum, we performed immunostaining on monkey and rat visual cortex. This new cat Fos antibody appears to be excellent for study of Fos expression as a marker for mapping neuronal activity in mammalian brain.

Animals↗
PubMed2006

In vivo two-photon imaging reveals a role of arc in enhancing orientation specificity in visual cortex.

Cortical representations of visual information are modified by an animal's visual experience. To investigate the mechanisms in mice, we replaced the coding part of the neural activity-regulated immediate early gene Arc with a GFP gene and repeatedly monitored visual experience-induced GFP expression in adult primary visual cortex by in vivo two-photon microscopy. In Arc-positive GFP heterozygous mice, the pattern of GFP-positive cells exhibited orientation specificity. Daily presentations of the same stimulus led to the reactivation of a progressively smaller population with greater reactivation reliability. This adaptation process was not affected by the lack of Arc in GFP homozygous mice. However, the number of GFP-positive cells with low orientation specificity was greater, and the average spike tuning curve was broader in the adult homozygous compared to heterozygous or wild-type mice. These results suggest a physiological function of Arc in enhancing the overall orientation specificity of visual cortical neurons during the post-eye-opening life of an animal.

Animals↗
PubMed1991

[The visual cortex of Tupaia: an alternative model?].

The tree shrew has become an interesting animal for research in neurobiology because of its unique structural and functional properties, in particular in its visual system. Some of these properties are described and discussed here as far as they are related to the functional architecture of the primary visual cortex: The representation of the ocularity, the ON and OFF responses, the development of the retino-geniculo-cortical projection, and synaptogenesis. From these data it appears that the tree shrew forms an important exception to the functional organization as it is found in standard experimental animals like cats and monkeys. It challenges a deeper thought on a common basis for both types of organization and development.

Animals↗
PubMed1997

Colour tuning in human visual cortex measured with functional magnetic resonance imaging.

The primate retina contains three classes of cones, the L, M and S cones, which respond preferentially to long-, middle- and short-wavelength visible light, respectively. Colour appearance results from neural processing of these cone signals within the retina and the brain. Perceptual experiments have identified three types of neural pathways that represent colour: a red-green pathway that signals differences between L- and M-cone responses; a blue-yellow pathway that signals differences between S-cone responses and a sum of L- and M-cone responses; and a luminance pathway that signals a sum of L- and M-cone responses. It might be expected that there are neurons in the primary visual cortex with response properties that resemble these three perceptual pathways, but attempts to find them have led to inconsistent results. We have therefore used functional magnetic resonance imaging (fMRI) to examine responses in the human brain to a large number of colours. In visual cortical areas V1 and V2, the strongest response is to red-green stimuli, and much of this activity is from neurons receiving opposing inputs from L and M cones. A strong response is also seen with blue-yellow stimuli, and this response declines rapidly as the temporal frequency of the stimulus is increased. These responses resemble psychophysical measurements, suggesting that colour signals relevant for perception are encoded in a large population of neurons in areas V1 and V2.

Brain Mapping↗
PubMed1988

Small lateral suprasylvian cortex lesions produce visual neglect and decreased visual activity in the superior colliculus.

Previous experiments in cats have shown that complete contralateral visual neglect is produced by removing all known visual cortex on one side of the brain, which can then be reversed by damaging the opposite superior colliculus. Presumably, descending facilitatory influences from the visual cortex to the ipsilateral superior colliculus are counterbalanced by intercollicular inhibition (Sprague: Science 153:1544-1546, '66). However, not all of visual cortex or all of the superior colliculus needs to be involved in this circuit. It is the deep rather than the superficial laminae of the superior colliculus that are primarily involved in visual attentive and orientation behaviors, and these laminae are largely independent of primary visual cortex. However, they do depend on corticotectal influences from a comparatively small extraprimary visual area of the posterior region of the lateral suprasylvian cortex (PSSC-Ogasawara et al: J. Neurophysiol. 52:1226-1245, '84). The present experiments demonstrate that lesions only a few millimeters in diameter in this corticotectal zone of the PSSC can produce profound visual neglect. While damage to this area has little, if any, effect on superficial laminae visual activity, it produces a dramatic decrease in the visual activity of the deep laminae. These cats with PSSC lesions fail to orient to a visual stimulus that is introduced suddenly into the contralateral visual field, yet they respond on nearly 100% of the trials to this same stimulus when it is presented in the ipsilateral visual field. The lesion-induced visual neglect produced by PSSC lesions is long-lasting but can be abruptly ameliorated by a midbrain lesion that primarily involves, or undercuts, the deep laminae of the contralateral superior colliculus. Thus, 1) visual neglect can be produced by depriving the deep laminae of the superior colliculus of visual inputs from the cortex, even when the principal visual cortical regions (17, 18, and 19) and their target structures are intact, and 2) visually guided behavior can be restored by eliminating afferents originating in, or passing through, the deep laminae of the contralateral superior colliculus.

Animals↗
PubMed2006

Isoflurane disrupts anterio-posterior phase synchronization of flash-induced field potentials in the rat.

Consciousness presumes a set of integrated functions such as sensory processing, attention, and interpretation, and may depend upon both local and long-range phase synchronization of neuronal activity in cerebral cortex. Here we investigated whether volatile anesthetic isoflurane at concentrations that produce loss of consciousness (LOC) disrupts long-range anterio-posterior and local anterior synchronization of neuronal activity in the rat. In six rats, deep electrodes were chronically implanted in the primary visual cortex (V1) and in two areas of the motor cortex (M1 and M2) for recording of intracortical event-related potentials (ERP). Thirty discrete flashes were presented at random interstimulus intervals of 15-45 s, and ERPs were recorded at stepwise increasing isoflurane concentrations of 0-1.1%. Neuronal synchronization was estimated using wavelet coherence computed from the ERP data band-pass filtered at 5-50 Hz. We found that (1) in the waking state, long-range anterio-posterior coherence in 5-25 Hz and 25-50 Hz frequency bands was significantly higher than local anterior coherence; (2) anterio-posterior coherence in both 5-25 Hz and 26-50 Hz bands was significantly reduced by isoflurane in a concentration-dependent manner; (3) local anterior coherence was not affected by isoflurane at any of the concentrations studied. These findings suggest that a disruption of long-range anterio-posterior rather than local anterior synchronization of neuronal activity precedes the anesthetic-induced loss of consciousness.

Anesthetics, Inhalation↗