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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↗
PubMed1983

Clustered intrinsic connections in cat visual cortex.

The intrinsic connections of the cortex have long been known to run vertically, across the cortical layers. In the present study we have found that individual neurons in the cat primary visual cortex can communicate over suprisingly long distances horizontally (up to 4 mm), in directions parallel to the cortical surface. For all of the cells having widespread projections, the collaterals within their axonal fields were distributed in repeating clusters, with an average periodicity of 1 mm. This pattern of extensive clustered projections has been revealed by combining the techniques of intracellular recording and injection of horseradish peroxidase with three-dimensional computer graphic reconstructions. The clustering pattern was most apparent when the cells were rotated to present a view parallel to the cortical surface. The pattern was observed in more than half of the pyramidal and spiny stellate cells in the cortex and was seen in all cortical layers. In our sample, cells made distant connections within their own layer and/or within another layer. The axon of one cell had clusters covering the same area in two layers, and the clusters in the deeper layer were located under those in the upper layer, suggesting a relationship between the clustering phenomenon and columnar cortical architecture. Some pyramidal cells did not project into the white matter, forming intrinsic connections exclusively. Finally, the axonal fields of all our injected cells were asymmetric, extending for greater distances along one cortical axis than along the orthogonal axis. The axons appeared to cover areas of cortex representing a larger part of the visual field than that covered by the excitatory portion of the cell's own receptive field. These connections may be used to generate larger receptive fields or to produce the inhibitory flanks in other cells' receptive fields.

Animals↗
PubMed2001

Colour-related oscillations in the striate cortex of awake monkeys: "reverse" observations.

Gamma oscillations of 30-70 Hz in local electroencephalograms (EEGs) were observed in primary visual cortex (V1) of monkeys when they viewed coloured stimuli under conditions which were not part of a training paradigm. No oscillatory modulations were detected in simultaneously recorded spike trains, although the latter responded to the stimuli. The oscillations had much longer latencies than the spike responses. Proceeding in a "reverse" manner, the oscillations were taken as primary elements of the analyses, and relationships to the accompanying behaviour were sought. Besides colour stimulation, the oscillations were found to be related to a form of annoyance. Only two of four monkeys showed the phenomena. We conclude that the oscillations had a central origin.

Action Potentials↗
PubMed2005

Postnatal expression profile of OBCAM implies its involvement in visual cortex development and plasticity.

This study examined the expression of a neuron-specific cell adhesion molecule, OBCAM (opioid-binding cell adhesion molecule), at both the mRNA and protein levels in the cat primary visual cortex at various postnatal ages, using cDNA array analysis and immunocytochemistry. Results obtained using both methods showed that the expression level of OBCAM was high in young and low in older and adult visual cortex. OBCAM-immunoreactivities were associated predominantly with perikarya and dendrites of pyramidal neurons, and OBCAM-immunopositive neurons were present in all cortical layers. Immunostaining of OBCAM in adult visual cortex showed a reduced number of immunopositive neurons and neurites and relatively lower staining intensities as compared with younger animals. In addition, the number of OBCAM-immunopositive neurons was significantly higher in the visual cortex of 4-month-old animals dark-reared from birth than those in age-matched normally reared animals. These results suggest that OBCAM may play an important role in visual cortex development and plasticity.

Aging↗
PubMed1978

Ocular dominance in layer IV of the cat's visual cortex and the effects of monocular deprivation.

1. The relation between the physiological pattern of ocular dominance and the anatomical distribution of geniculocortical afferents serving each eye was studied in layer IV of the primary visual cortex of normal and monocularly deprived cats. 2. One eye was injected with radioactive label. After allowing sufficient time for transeuronal transport, micro-electrode recordings were made, and the geniculocoritcal afferents serving the injected eye were located autoradiographically. 3. In layer IV of normal cats, cell were clustered according to eye preference, and fewer cells were binocularly driven than in other layers. Points of transition between groups of cells dominated by one eye and those dominated by the other were marked with electrolytic lesions. A good correspondence was found between the location of cells dominated by the injected eye and the patches of radioactively labelled geniculocortical afferents. 4. Following prolonged early monocular deprivation, the patches of geniculocortical afferents in layer IV serving the deprived eye were smaller, and those serving the non-deprived eye larger, than normal. Again there was a coincidence between the patches of radioactively labelled afferents and the location of cells dominated by the injected eye. 5. The deprived eye was found to dominate a substantial fraction (22%) of cortical cells in the fourth layer. In other cortical layers, only 7% of the cells were dominated by the deprived eye. 6. These findings suggest that the thalamocortical projection is physically rearranged as a consequence of monocular deprivation, as has been demonstrated for layer IVc of the monkey's visual cortex (Hubel, Wiesel & Le Vay, 1977).

Animals↗
PubMed1994

Lamina-specific expression and activity-dependent regulation of seven GABAA receptor subunit mRNAs in monkey visual cortex.

Seven monkey-specific GABAA receptor subunit cDNAs were isolated and cloned; radioactive cDNA and cRNA probes derived from them were used for Northern blot analysis and in situ hybridization histochemistry of the primary visual cortex (area 17), with comparative observations on other cortical areas. cDNAs corresponding to alpha 1, alpha 2, alpha 4, alpha 5, beta 1, beta 2, and gamma 2 GABAA receptor subunits were isolated and had sequences unique to the monkey but recognized mRNAs of distinct molecular weights consistent with those reported in other species. mRNAs for the alpha 1, beta 2, and gamma 2 subunits were expressed at much higher levels in area 17 than in motor, somatosensory, or temporal association cortex, possibly reflecting the greater density of GABA cells and synapses in area 17. In areas 17 and 18, each of the seven subunit mRNAs showed individually distinct patterns of laminar distribution. alpha 1, beta 2, and gamma 2 subunit mRNAs, which are thought to form the basis of receptors with the full range of classical GABAA receptor properties in the adult, were particularly enriched in layers II-III, IVC, and VI of area 17, following patterns of receptor distribution previously demonstrated by radioligand binding and immunocytochemistry. alpha 2, alpha 4, alpha 5, and beta 1 transcripts had quite different localization patterns that did not match the antoradiographic or immunocytochemical receptor localization patterns. alpha 2 and alpha 5 subunit mRNAs, which are thought to be the subunits mainly expressed in development, were enriched in layer VI and the underlying white matter, possibly reflecting the involvement of receptors formed from alpha 2 and alpha 5 polypeptides in trophic interactions in the cortical subplate zone during development of the cerebral cortex. Following 8-21 d periods of monocular deprivation induced by intravitreal injection of TTX, levels of alpha 1, beta 2, and gamma 2 subunit mRNAs were substantially reduced in deprived ocular dominance columns of layer IVC in area 17. The effect was greatest for the alpha 1 subunit; for both alpha 1 and gamma 2 subunit mRNAs, it extended into deprived rows of cytochrome oxidase-identified periodicities in other layers. Apart from the alpha 5 subunit mRNA, which showed reduced levels in layer VI, the other subunit mRNAs were unaffected by monocular deprivation. These results demonstrate the heterogeneity of GABAA receptor subunit expression in a complex, multilaminar cortical area. They suggest that receptors with different functional properties may be assembled from different combinations of subunit polypeptides in different layers and show that subunit expression is differentially regulated under activity-dependent conditions.

Animals↗
PubMed2004

Neuroplasticity after unilateral visual cortex damage in the newborn cat.

Anatomical, electrophysiological, and behavioral studies implicate extrastriate cortex as a major contributor to the sparing of visually guided behaviors following lesions of primary visual cortex incurred early in life. Here we report considerable sparing of the ability to detect and localize stimuli in the hemifield contralateral to unilateral early lesions of all contiguous visually-responsive primary and extrastriate cortical regions (occipital, visuoparietal, and visuotemporal cortices). In the adult cat this same lesion induces a dense blindness and cats are unable to orient to any visual stimulus introduced into the contralesional hemifield. In the absence of cortical circuits, the neural sparing identified following the neonatal lesion is based on the superior colliculus and it occurs despite massive retrograde transynaptic degeneration of large numbers of retinal ganglion cells.

Animals↗
PubMed2004

Cognitive- and motor-related regions in Parkinson's disease: FDOPA and FDG PET studies.

OBJECTIVE: Using 6-[(18)F]fluoro-L-dopa (FDOPA) and [(18)F]fluorodeoxyglucoce (FDG) positron emission tomography (PET), multiple regression analyses were performed to determine the specific brain regions that are related to cognitive and motor symptoms in nondemented patients with Parkinson's disease. METHODS: Spatially normalized images of FDOPA influx rate constant (Ki) values and relative regional cerebral metabolic rates for glucose (rrCMRglc) were created. Raven's Coloured Progressive Matrices (RCPM) scores and the Unified Parkinson's Disease Rating Scale (UPDRS) motor scores were used to determine the patients' cognitive and motor functions, respectively. Multiple correlation analyses between the FDOPA and FDG images and the cognitive and motor scores were performed for each voxel. RESULTS: RCPM score was significantly positively correlated with the FDOPA Ki in the left hippocampus and with the rrCMRglc in the left middle frontal gyrus and right retrosplenial cortex. Motor function was significantly positively correlated with the FDOPA Ki in the bilateral striatum and with the rrCMRglc in association areas and primary visual cortex. The level of motor function was significantly inversely correlated with the FDOPA Ki in the anterior cingulate gyrus and with the rrCMRglc in bilateral primary motor cortex and right putamen. CONCLUSIONS: Changes of striatal FDOPA uptake and rrCMRglc in the primary motor cortex likely represent dysfunction in the motor system involving the corticobasal ganglia-thalamocortical loop. Change of FDOPA uptake in the anterior cingulate gyrus may be related to up-regulation of dopamine synthesis in surviving dopamine neurons. The regions where correlation with cognitive function was observed belong to a cognitive frontoparietal-hippocampal network.

Biological Transport↗
PubMed2005

Dose-dependent decrease of activation in bilateral amygdala and insula by lorazepam during emotion processing.

BACKGROUND: Functional neuroimaging may elucidate the pathophysiologic features of anxiety disorders and the site of action of anxiolytic drugs. A large body of evidence suggests that the amygdala and associated limbic structures play a critical role in the expression of anxiety and may be treatment targets for anxiolytic drugs. OBJECTIVE: To determine whether lorazepam dose-dependently attenuates blood oxygenation level-dependent functional magnetic resonance imaging (BOLD fMRI) activation in the amygdala and associated limbic structures during an emotion face assessment task. PARTICIPANTS AND DESIGN: Fifteen healthy volunteers participated in a double-blind, placebo-controlled, randomized dose-response study. Subjects underwent imaging 3 times (at least a week apart) and were given either a single-dose placebo or 0.25 mg or 1.0 mg of lorazepam 1 hour prior to an MRI session. During fMRI, subjects completed an emotion face assessment task, which has been shown to elicit amygdala activation. MAIN OUTCOME MEASURES: The BOLD-fMRI activation in amygdala, insula, and medial prefrontal cortex during the emotion face assessment task. RESULTS: Lorazepam significantly attenuated the BOLD-fMRI signal in a dose-dependent manner in bilateral amygdala and insula but not in the medial prefrontal cortex. Lorazepam did not affect the BOLD-fMRI signal in the primary visual cortex. CONCLUSIONS: The current finding provides the first neuroimaging evidence of a dose-dependent change induced by an established therapeutic agent in brain regions known to be critical for the mediation of anxiety. This investigation may help to support the use of BOLD-fMRI with pharmacological probes to investigate the neural circuits underlying anxiety and the use of fMRI as a tool in the development of new anxiolytic agents.

Adolescent↗
PubMed2006

A developmental model of ocular dominance column formation on a growing cortex.

We derive an activity-based developmental model of ocular dominance column formation in primary visual cortex that takes into account cortical growth. The resulting evolution equation for the densities of feedforward afferents from the two eyes exhibits a sequence of pattern forming instabilities as the size of the cortex increases. We use linear stability analysis to investigate the nature of the transitions between successive patterns in the sequence. We show that these transitions involve the splitting of existing ocular dominance (OD) columns, such that the mean width of an OD column is approximately preserved during the course of development. This is consistent with recent experimental observations of postnatal growth in cat.

Algorithms↗
PubMed1993

Development and regulation of beta adrenergic receptors in kitten visual cortex: an immunocytochemical and autoradiographic study.

The developmental pattern and laminar distribution of beta 1 and beta 2 adrenergic receptor subtypes were studied in cat visual cortex with autoradiography using [125I]iodocyanopindolol as a ligand and also with immunocytochemistry using a monoclonal antibody directed against beta adrenergic receptors. In the primary visual cortex of adult cats, the laminar distributions of both beta 1 and beta 2 adrenergic receptors revealed by autoradiography were very similar, with concentrations in layers I, II, III and VI. In young kittens (postnatal days 1 and 10), fewer beta adrenergic receptors were present, and they were concentrated in the deep cortical layers (V-VI) and subcortical white matter. Between postnatal days 15 and 40, beta adrenergic receptors increased in density more quickly in the superficial layers than they did in the deep and middle cortical layers. By postnatal day 40, the adult pattern was achieved, with two bands of intense binding in the superficial and deep cortical layers and a lower density in layer IV. Immunocytochemical techniques applied to adult cat cortex showed that beta adrenergic receptor-like immunoreactivity was found in different populations of neurons and glial cells. The immunoreactive neural cells were most dense in layers II, III and VI. About 50% of these immunoreactive neural cells were glial cells, primarily astrocytes. Immunoreactive pyramidal cells were mostly located in layers III and V. In layer IV, many stellate cells were stained. Immunoreactive astrocytes in the subplate and white matter progressively increased in number during development until adulthood. The pattern of laminar distribution and the developmental process was not affected by interrupting noradrenergic innervation from locus coeruleus either before or after the critical period. However, when visual input was interrupted by lesions of the lateral geniculate nucleus in young kittens (postnatal day 10), the density of both beta adrenergic receptor subtypes decreased significantly in the deep cortical layers. Lateral geniculate nucleus lesions in adult cats resulted in a pronounced decrease in beta adrenergic receptor density in layer IV.

Aging↗
PubMedDate not supplied

Visual cortex neurons in monkeys and cats: detection, discrimination, and identification.

A descriptive function method was used to measure the detection, discrimination, and identification performance of a large population of single neurons recorded from within the primary visual cortex of the monkey and the cat, along six stimulus dimensions: contrast, spatial position, orientation, spatial frequency, temporal frequency, and direction of motion. First, the responses of single neurons were measured along each stimulus dimension, using analysis intervals comparable to a normal fixation interval (200 ms). Second, the measured responses of each neuron were fitted with simple descriptive functions, containing a few free parameters, for each stimulus dimension. These functions were found to account for approximately 90% of the variance in the measured response means and response standard deviations. (A detailed analysis of the relationship between the mean and the variance showed that the variance is proportional to the mean.) Third, the parameters of the best-fitting descriptive functions were utilized in conjunction with Bayesian (optimal) decision theory to determine the detection, discrimination, and identification performance for each neuron, along each stimulus dimension. For some of the cells in monkey, discrimination performance was comparable to behavioral performance; for most of the cells in cat, discrimination performance was better than behavioral performance. The behavioral contrast and spatial-frequency discrimination functions were similar in shape to the envelope of the most sensitive cells; they were also similar to the discrimination functions obtained by optimal pooling of the entire population of cells. The statistics which summarize the parameters of the descriptive functions were used to estimate the response of the visual cortex as a whole to a complex natural image. The analysis suggests that individual cortical neurons can reliably signal precise information about the location, size, and orientation of local image features.

Animals↗
PubMed2000

Coexistence of linear zones and pinwheels within orientation maps in cat visual cortex.

Revealing the layout of cortical maps is important both for understanding the processes involved in their development and for uncovering the mechanisms underlying neural computation. The typical organization of orientation maps in the cat visual cortex is radial; complete orientation cycles are mapped around orientation singularities. In contrast, long linear zones of orientation representation have been detected in the primary visual cortex of the tree shrew. In this study, we searched for the existence of long linear sequences and wide linear zones within orientation preference maps of the cat visual cortex. Optical imaging based on intrinsic signals was used. Long linear sequences and wide linear zones of preferred orientation were occasionally detected along the border between areas 17 and 18, as well as within area 18. Adjacent zones of distinct radial and linear organizations were observed across area 18 of a single hemisphere. However, radial and linear organizations were not necessarily segregated; long (7.5 mm) linear sequences of preferred orientation were found embedded within a typical pinwheel-like organization of orientation. We conclude that, although the radial organization is dominant, perfectly linear organization may develop and perform the processing related to orientation in the cat visual cortex.

Animals↗
PubMed2002

Plasticity of the visual cortex after injury: what's different about the young brain?

The repercussions of localized injury of the cerebral cortex in young brains differ from the repercussions triggered by equivalent damage of the mature brain. In the young brain, some distant neurons are more vulnerable to the lesion, whereas others survive and expand their projections to bypass damaged and degenerated structures. The net result is sparing of neural processing and behaviors. This article summarizes both the modifications in visual pathways resulting from visual cortex lesions sustained early in life and the neural and behavioral processes that are spared or permanently impaired. Experiments using reversible deactivation show that at least two highly localizable functions of normal cerebral cortex are remapped across the cortical surface as a result of an early lesion of the primary visual cortex. Moreover, the redistributions have spread the essential neural operations underlying orienting behavior from the visual parietal cortex to a normally functionally distinct type of cortex in the visual temporal system, and in the opposite direction for complex-pattern recognition. Similar functional reorganizations may underlie sparing of neural processes and behavior following early lesions in other cerebral systems, and these other systems may respond well to emerging therapeutic strategies designed to enhance the sparing of functions.

Aging↗
PubMed2006

Tuning for spatiotemporal frequency and speed in directionally selective neurons of macaque striate cortex.

We recorded the responses of direction-selective simple and complex cells in the primary visual cortex (V1) of anesthetized, paralyzed macaque monkeys. When studied with sine-wave gratings, almost all simple cells in V1 had responses that were separable for spatial and temporal frequency: the preferred temporal frequency did not change and preferred speed decreased as a function of the spatial frequency of the grating. As in previous recordings from the middle temporal visual area (MT), approximately one-quarter of V1 complex cells had separable responses to spatial and temporal frequency, and one-quarter were "speed tuned" in the sense that preferred speed did not change as a function of spatial frequency. Half fell between these two extremes. Reducing the contrast of the gratings caused the population of V1 complex cells to become more separable in their tuning for spatial and temporal frequency. Contrast dependence is explained by the contrast gain of the neurons, which was relatively higher for gratings that were either both of high or both of low temporal and spatial frequency. For stimuli that comprised two spatially superimposed sine-wave gratings, the preferred speeds and tuning bandwidths of V1 neurons could be predicted from the sum of the responses to the component gratings presented alone, unlike neurons in MT that showed nonlinear interactions. We conclude that spatiotemporal modulation of contrast gain creates speed tuning from separable inputs in V1 complex cells. Speed tuning in MT could be primarily inherited from V1, but processing that occurs after V1 and possibly within MT computes selective combinations of speed-tuned signals of special relevance for downstream perceptual and motor mechanisms.

Action Potentials↗
PubMed2004

A semi-persistent adult ocular dominance plasticity in visual cortex is stabilized by activated CREB.

The adult cerebral cortex can adapt to environmental change. Using monocular deprivation as a paradigm, we find that rapid experience-dependent plasticity exists even in the mature primary visual cortex. However, adult cortical plasticity differs from developmental plasticity in two important ways. First, the effect of adult, but not juvenile monocular deprivation is strongly suppressed by administration of barbiturate just prior to recording visual evoked potentials, suggesting that the effect of adult experience can be inactivated acutely. Second, the effect of deprivation is less persistent over time in adults than in juveniles. This correlates with the known decline in CREB function during maturation of the visual cortex. To compensate for this decline in CREB function, we expressed persistently active VP16-CREB and find that it causes adult plasticity to become persistent. These results suggest that in development and adulthood, the regulation of a trans-synaptic signaling pathway controls the adaptive potential of cortical circuits.

Aging↗
PubMed2001

[The visual cortex alpha-scanning: EEG and magnetic resonance tomography data].

Exact localization of equivalent current dipoles (ECD) was obtained by combining the EEG and the MRI mapping allowing to trace the ECG displacement over the cortex. The data obtained corroborate localization of the alpha-rhythm ECD in the Gyrus Calcarina: the human primary visual cortex. Successive shifts of the ECD over this area during generation of each alpha-wave, were revealed. The data are discussed in the light of the "scanning hypothesis" that predicted a certain functional meaning of the alpha-wave spreading for cortical processing of sensory information.

Adult↗
PubMed1993

Transient cortical pathways in the pyramidal tract of the neonatal ferret.

Anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) was used to study transient axons from the visual cortex in the pyramidal tract. Injections at birth restricted to the visual cortex labeled axons in the vicinity of the pontine nuclei. Two to eight days after birth, axons from the occipital cortex were found posterior to the pontine nucleus, their caudalmost stable target. Transient corticospinal axons from the presumptive primary visual cortex did not grow caudal to the pyramidal decussation. Innervation of more distal targets preceded innervation of proximal targets. Innervation of the pontine nucleus is initiated around 68 hours after birth, when the transient extension in the medullary pyramidal tract has attained its maximum caudal extent. Innervation of the superior colliculus begins 9 days after birth. Retrograde tracers were used to follow the developmental changes in the cortical distribution of the parent neurons giving rise to axons in the pyramidal tract. In the adult, labeled neurons following injection of retrograde tracer in the pyramidal tract occupied less than a third of the neocortex and were centred on the anterior part of the coronal and spleniocruciate gyri. In the immature brain, labeled neurons covered more than two-thirds of the neocortex. Areal density measurements in the neonate showed that peak labeling was centred in the anterior coronal and spleniocruciate gyri, where corticospinal cells in the adult are located. There was a marked rostral-caudal gradient so that labeled neurons were very scarce towards the occipital pole. These results, showing transient neocortical axons in the pyramidal tract in a carnivore, suggest that this may be a common feature of mammalian development. The finding that the adult pattern of corticospinal projections does not emerge from a uniform distribution is discussed with respect to the areal specification of cortical connectivity.

Animals↗