Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “cortical structure”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 415 records · Page 23Linked to original sources
PubMed2000

Neural mechanisms of visual feature grouping.

The present work relates compositions of visual scenes to signals in visual cortex and to cortical circuit models in order to understand neural mechanisms of perceptual feature grouping. It starts from the hypothesis that synchronization and decoupling of cortical gamma-activities (35-90 Hz) define the relations among visual objects. Here we concentrate on synchronization related to two basic visual situations, (1.) static retinal stimulation during ocular fixation, and (2.) transient stimulation during sudden luminance modulations or shifts in object position. For testing the synchronization hypothesis we investigated signal correlations of multiple micro-electrode recordings in visual cortex areas V1 and V2 of behaving monkeys. Static retinal stimuli induce gamma-activities that are loosely phase-coupled among neighboring neural populations of an object's cortical representation. This can explain why synchronization, measured by spectral coherence, is restricted to few millimeters cortex. Such patches of gamma-synchronization become de-coupled across the representation of an object's contour, and thereby can code figure-ground segregation. Transient stimuli evoke synchronized volleys of stimulus-locked activities that are typically non-rhythmic and include low frequency components in addition to those in the gamma-range. It is argued why stimulus-induced and stimulus-locked phase-coupled activations are both appropriate for supporting perceptual feature grouping. Clues for basic neural mechanisms participating in feature grouping are provided by our biologically motivated simulations of synchronization in cortical structures. (1.) Local populations generate gamma-oscillations via feedback inhibition during states of static retinal stimulation. (2.) Bidirectional facilitatory connections serve for phase-coupling among neighboring neural populations. (3.) Spike transmission delays, increasing with cortical distance, can explain the restriction of gamma-coherence to patches of few millimeters cortex. (4.) The size of synchronization patches in one visual area (e.g., V1) can define the size of classical receptive fields at the consecutive level of visual processing (V2) if Hebbian learning is operative. This may explain the increase in receptive field size at consecutive levels of visual processing. In conclusion, our results and those of others are supportive for the hypothesis that phase-coupled gamma-signals can code feature grouping and object continuity. However, convincing experimental proofs showing directly the dependence of perceptual grouping on cortical phase-coupling are still lacking.

Animals↗
PubMed1990

Is postischemic hypoperfusion related to brain edema?

The effect of reversible cerebral ischemia on brain edema development was studied with a gravimetric method. CBF changes after ischemia were correlated with alterations in brain SG. Forebrain ischemia (15 min) was induced in rats by reversible bilateral ligation of both carotid arteries plus induction of controlled hypotension to 50 mm Hg. The SG of different brain structures was determined in a Percoll column up to 24 hr after ischemia. In addition, rCBF was measured by [14C]iodoantipyrine autoradiography. Cerebral ischemia resulted in reduction of CBF to less than 1% of normal in cortical structures and the caudatoputamen. One hour after the end of ischemia, blood flows were still reduced to 30% to 50% of the control level indicative of DPH. SG in cortex and hypothalamus reached a maximal decrease 10 min after the end of the ischemia and was still significantly reduced at 1 hr, although it was normal again 6 hr later. Regression analysis revealed a significant correlation between CBF obtained during ischemia and the corresponding SG found at 10-min recirculation, which could also be established at 1-hr recirculation. Therefore, a causal relation between the development of the DPH and the formation of ischemia might be considered.

Animals↗
PubMed1996

Reproducible sampling regimen for specific cortical regions: application to speech-associated areas.

The variability in the external gyri pattern of human brains has made the identification of specific cortical areas difficult. Studies correlating cortical structure and function have not consistently controlled for this variability. The aim of the present study was to develop a reliable and reproducible regimen for sampling five speech-associated and one non-speech associated cortical region in the human brain. The gyri of interest were labelled using non-aqueous dye prior to coronal slicing of brains at 3 mm intervals. Using the labelled gyri, a set of internal brain landmarks was established to aid in sampling one block of each cortical region of interest. The position of each internal landmark was determined as a percentage of the total brain length and breadth. The variability in the position of each internal landmark was investigated using analysis of variance and found to be consistent in three dimensions in all cases. The correlation of the sampled cortical region to the internal landmark was consistent in different cases with point to point agreement of 100%. This contrasts with the variability between cases in external gyri features. The sampled region was tested to determine cytoarchitectural variability by measuring the depth of each cortical layer. This technique found that the same cytoarchitectural regions were sampled in each case. As expected, these regions were distinguishable by the significant difference in the depth of different cortical layers. Accurate identification of both the external gyri and internal landmarks occurred with interrater point to point agreement of 90-100%.

Adolescent↗
PubMed2005

Multisensory contributions to low-level, 'unisensory' processing.

Neurobiologists have traditionally assumed that multisensory integration is a higher order process that occurs after sensory signals have undergone extensive processing through a hierarchy of unisensory subcortical and cortical regions. Recent findings, however, question this assumption. Studies in humans, nonhuman primates and other species demonstrate multisensory convergence in low level cortical structures that were generally believed to be unisensory in function. In addition to enriching current models of multisensory processing and perceptual functions, these new findings require a revision in our thinking about unisensory processing in low level cortical areas.

Animals↗
PubMed1977

Immunohistochemical studies on the localization and distribution of monoamine neuron systems in the rat brain II. Tyrosine hydroxylase in the telencephalon.

Extensive plexuses of TH-positive nerve terminals were found in many parts of the telencephalon, mainly confined to the subcortical and limbic cortical structures. Of special interest were the distinct networks of varying densities in the amygdaloid cortex, the entorhinal cortex, the prepiriform cortex, the anterior cingulate cortex and the (pre-)frontal cortex. Their distribution is identical with the patterns observed in recent studies on cortical dopamine nerve terminals using certain modifications of the Falck-Hillarp technique. The extremely dense TH innervations patterns of the caudate nucleus, nucleus accumbens, tuberculum olfactorium and the less dense basket-like innervation of the lateral septal nuclei could also be demonstrated. TH-positive cell bodies in a periglomerular position could be observed in the olfactory bulb. A few TH-positive cell bodies were observed in the area around the anterior commissure and in the cingulate cortex. In one area, the hippocampal formation, TH-positive dotlike structures were located in the position of the mossy fibres. In all probability they do not belong to monoamine neurons but may contain a cross-reacting protein. In general, the distribution and density of TH-positive terminals agrees well with extensive regional, biochemical studies on TH activity performed by other groups. Minor discrepancies are discussed. As stated in a parallel study on the distribution of TH in the mes- and diencephalon these findings indicate that TH activity is closely related to the amount of enzyme protein. The TH enzyme levels seem to be much higher in the DA than in the NA nerve terminals of the forebrain which would explain the preferential demonstration of DA terminals in the forebrain using TH antiserum and the high and low TH enzyme activity in DA and NA rich regions, respectively.

Animals↗
PubMed1993

Autoradiographic localization of prazosin and rauwolscine binding sites in the human kidney.

In the human kidney, binding sites for the alpha 1-adrenoceptor antagonist 3H-prazosin and the alpha 2-adrenoceptor antagonist 3H-rauwolscine were localized and quantified by in vitro autoradiography. 3H-prazosin binding was found predominantly in the renal cortex. In the medulla, tubular structures were also specifically labelled. No binding sites, however, were detected in association with glomeruli or large blood vessels. 3H-rauwolscine labelled the medullary vascular bundles intensively, but no binding sites were associated with glomeruli or other cortical structures. Thus, the binding pattern for 3H-prazosin is quite similar in both human and rat renal cortex. There are, however, distinct differences between human and rat kidneys in the distribution of the alpha 2-adrenergic binding sites visualized with the antagonist 3H-rauwolscine.

Animals↗
PubMed2004

Ubiquitin and ubiquitin-related proteins in the brains of patients with atypical Pick's disease without Pick bodies and dementia with motor neuron disease.

Nine cases of atypical Pick's disease without Pick bodies (aPiD) and seven cases of dementia with motor neuron diseases (D-MND) were compared using immunohistochemistry of ubiquitin (ub) and ub-related proteins. All cases showed rostral-dominant atrophy in the temporal and frontal lobes, although the degree of atrophy with neuronal loss was much more severe in the aPiD cases. In both aPiD and D-MND cases, ub-positive and tau-negative structures were found mainly in the hippocampal dentate gyrus and cerebral cortex. Granular cells of the dentate gyrus showed similar ub-positive intraneuronal inclusions in both cases. In the aPiD cases, most of the ub-positive cortical structures were ub-positive dendrites in layers II-IIIab and layers V-VI, although some neurons also showed diffuse ub-positive staining in the cytoplasm. In the D-MND cases, some neurons showed ub-positive inclusions in layers II-IIIab, and ub-positive dendrites were unremarkable. The number of ub-positive neurons and dendrites in relation to the degree of neuronal loss in the cerebral cortex were then evaluated. The number of ub-positive neurons in the regions showing very mild to mild neuronal loss was significantly greater in the D-MND cases than in the aPiD cases. However, in the aPiD cases, the number of ub-positive neurons was significantly greater in the regions showing moderate neuronal loss. When double-immunostained, almost all ub-positive structures were positive for ub-binding protein p62. Some ub-positive or negative neurons in the cerebral cortex were immunostained with anti-ub ligase (Parkin) and anti-ub C-terminal hydrolase (UCH-L1) antibodies. Granular cells of the dentate gyrus were weakly positive for UCH-L1. There could be some differences in the mechanism by which neurons in the cerebral cortex accumulate ub between aPiD and D-MND.

Adult↗
PubMed2003

Anatomical mechanisms and functional implications of multisensory convergence in early cortical processing.

Recent findings in both monkeys and humans indicate that multisensory convergence occurs in low-level cortical structures generally believed to be unisensory in function. In an in-depth treatment of this theme, this paper reviews anatomical and physiological findings relating to the convergence of visual, somatosensory and auditory signals at early stages of auditory cortical processing. We discuss the potential anatomical sources of the input, and the types of known projections, and attempt to integrate this information with the current hierarchical model of auditory processing. Finally, we consider the functional implications of multisensory integration in early sensory processing.

Animals↗
PubMed2002

Seizures in paediatric Chiari type I malformation: the role of single-photon emission computed tomography.

UNLABELLED: Chiari type I malformation is one of the posterior fossa maldevelopments with which different clinical manifestations have been associated. Seizures have only recently been associated with Chiari type I malformation. This study reports on 4 children with epilepsy (2M, 2F; age range 8-15 y) diagnosed with Chiari type I malformation by brain magnetic resonance imaging (MRI), in whom no cortical structural involvement was observed. In these patients an interictal ethylcysteinate-dimer-single-photon emission computed tomographic (ECD-SPECT) study was performed to define more precisely the relationship between Chiari type I malformation and seizures. In these patients the hypoperfusion area correlated with electroencephalographic (EEG) focal abnormalities. These hypoperfusions may represent the functional aspect of a cerebral microdysgenesis; seizures and EEG epileptic anomalies may also be linked to the complex network connection between cortices and cerebellar hemispheres. A cerebellar hypoperfusion was also detected in two of the four examined patients, indicating a functional or structural involvement. CONCLUSION: Interictal SPECT scans are helpful for the clarification of seizures in patients with Chiari type I malformation.

Adolescent↗
PubMed1987

Prognostic value of early cortical somatosensory evoked potentials after resuscitation from cardiac arrest.

Short-latency somatosensory evoked potentials (SEPs) were evaluated in patients after cardiorespiratory arrest to study their pattern of recovery in the acute stage of anoxic-ischaemic coma. Fifty consecutive comatose patients were investigated within 8 h after cardiorespiratory resuscitation. In 30 patients no cortical SEPs were recorded and none of the patients recovered cognition. In 20 patients cortical SEPs were recorded and 5 recovered. The different susceptibility of frontal and parietal cortical structures to anoxia was reflected by the dissociated loss of parietal or frontal potentials in 6 patients. Post-mortem pathology in 15 patients confirmed extensive anoxic-ischaemic damage of cerebral and cerebellar cortex and thalamus in patients without cortical SEPs whereas the histological lesions were restricted to Sommer's sector and Purkinje cells in those with preserved SEPs. SEPs thus reflect the extent of brain damage after cardiorespiratory resuscitation.

Adult↗
PubMedDate not supplied

Three-dimensional reconstruction of the auditory cortical areas from magnetic resonance images.

The future of neuromagnetic research will be highly dependent on the development of analysis procedures utilizing morphological information derived from magnetic resonance (MR) images. However, constraining the biomagnetic inverse problem by using such information may lead to serious misinterpretations if the reconstruction algorithm for the cortical surface overlooks boundaries between grey matter and cerebrospinal fluid (CSF) or artificially generates them. The purpose of this study was to check as to what extent an advanced automatic three-dimensional reconstruction procedure is able to segment the cortical structures located hidden in the Sylvian fissure (especially Heschl's gyrus and planum temporale). The procedure consisted of four processes: a coarse segmentation, a refined segmentation of the white matter, a skeletonization of the sulci and a segmentation of the cortical surface by concurrent region growing for brain and CSF. The reconstruction result for single slices basically agrees with the impression obtained upon visual inspection of the original MR data. Photorealistic visualizations, showing a good qualitative agreement with anatomical images, suggest that the reconstructed surfaces are realistic and detailed enough to be applicable in source analyses of auditory evoked fields.

Adult↗
PubMed1996

Digit removal leads to discrepancies between the structural and functional organization of the forepaw barrel subfield in layer IV of rat primary somatosensory cortex.

The physiological representation of the forepaw in rat primary somatosensory cortex (SI) is topographically organized. This representation is associated with the unique arrangement of barrels in layer IV of the forepaw barrel subfield (FBS) in SI and provides an example of a relationship between cortical structure and function. It has been reported that removal of peripheral afferent input to the FBS prior to postnatal day 5 or 6 results in a disorganized FBS, while deafferentation at later times produces little or no alteration of the FBS. Therefore, restricted deafferentations of individual digits in adult rats should result in little, if any, disruption of the FBS, while at the same time eliminating afferent input to the FBS from a localized region of the periphery. This manipulation is likely to create a mismatch between structure and function and offer insight into what barrels actually represent in the adult deafferent. In the present study, we amputated digit three (D3) in eight adult rats, allowed a 1-month survival time, physiologically mapped the representation of D2, D4, and the stump, and compared this physiological map to the underlying barrels in the FBS. Our results showed that FBS barrels formerly associated with the representation of D3 were now associated with the representation of surrounding digits D2 and D4, as well as the remaining stump. By superimposing the morphological and physiological map upon one another, it was clear that the D2 and D4 representations expanded into the former D3 barrel territory and septae between the barrels. The reorganized physiological map was somatotopically organized, even though the general configuration of the morphological map remained unaltered, as visualized with cytochrome oxidase staining. These results suggest that in the deafferent, neurons within FBS barrels previously associated with the representation of punctate regions of skin become associated with neighboring regions of skin. A morphological substrate to account for this cortical reorganization is described.

Amputation, Surgical↗
PubMed2001

Multiple microelectrode-recording system for human intracortical applications.

The human brain is dominated by the neocortex, a large folded surface, whose cellular and synaptic elements are arranged in layers. Since cortical structure is relatively constant across its surface, local information processing can be inferred from multiple laminar recordings of its electrical activity along a line perpendicular to its surface. Such recordings need to be spaced at least as close together as the cortical layers, and need to be wideband in order to sample both low frequency synaptic currents as well as high-frequency action potentials. Finally, any device used in the human brain must comply with strict safety standards. The current paper presents details of a system meeting these criteria, together with sample results obtained from epileptic subjects undergoing acute or chronic intracranial monitoring for definition of the epileptogenic region.

Action Potentials↗
PubMed1993

Cortactin, an 80/85-kilodalton pp60src substrate, is a filamentous actin-binding protein enriched in the cell cortex.

Two related cellular proteins, p80 and p85 (cortactin), become phosphorylated on tyrosine in pp60src-transformed cells and in cells stimulated with certain growth factors. The amino-terminal half of cortactin is comprised of multiple copies of an internal, tandem 37-amino acid repeat. The carboxyl-terminal half contains a distal SH3 domain. We report that cortactin is an F-actin-binding protein. The binding to F-actin is specific and saturable. The amino-terminal repeat region appears to be both necessary and sufficient to mediate actin binding, whereas the SH3 domain had no apparent effect on the actin-binding activity. Cortactin, present in several different cell types, is enriched in cortical structures such as membrane ruffles and lamellipodia. The properties of cortactin indicate that it may be important for microfilament-membrane interactions as well as transducing signals from the cell surface to the cytoskeleton. We suggest the name cortactin, reflecting the cortical subcellular localization and its actin-binding activity.

Actins↗
PubMed1988

Is postischaemic water accumulation related to delayed postischaemic hypoperfusion in rat brain?

The effect of reversible cerebral ischaemia on brain oedema development was studied with a gravimetric method. Cerebral blood flow changes after ischaemia were correlated with alterations in brain specific gravity. Forebrain ischaemia (15 min) was induced in rats by reversible bilateral ligation of both carotid arteries plus induction of controlled hypotension to 50 mm Hg. The specific gravity of different brain structures was determined in a Percoll column up to 24 h after ischaemia. In addition, regional cerebral blood flow was measured by 14C-iodoantipyrine autoradiography. Cerebral ischaemia resulted in reduction of cerebral blood flow to less than 1% of normal in cortical structures and the caudatoputamen. One hour after the end of ischaemia blood flows were still reduced to 30-50% of the control level indicative of delayed postischaemic hypoperfusion. Specific gravity in cortex and hypothalamus reached a maximal decrease 10 min after the end of the ischaemia, and was still significantly reduced at 1 h, while it was normal again 6 hrs later. Regression analysis between regional cerebral blood flows and the corresponding specific gravities were made at various time points, but no significant correlations could be established. Other mechanisms, like vasoconstriction, rheologic or metabolic factors may be causative for the delayed postischaemic hypoperfusion.

Animals↗
PubMed1996

Function of spindle microtubules in directing cortical movement and actin filament organization in dividing cultured cells.

The mitotic spindle has long been recognized to play an essential role in determining the position of the cleavage furrow during cell division, however little is known about the mechanisms involved in this process. One attractive hypothesis is that signals from the spindle may function to induce reorganization of cortical structures and transport of actin filaments to the equator during cytokinesis. While an important idea, few experiments have directly tested this model. In the present study, we have used a variety of experimental approaches to identify microtubule-dependent effects on key cortical events during normal cell cleavage, including cortical flow, reorientation of actin filaments, and formation of the contractile apparatus. Single-particle tracking experiments showed that the microtubule disrupting drug nocodazole induces an inhibition of the movements of cell surface receptors following anaphase onset, while the microtubule stabilizing drug taxol causes profound changes in the overall pattern of receptor movements. These effects were accompanied by a related set of changes in the organization of the actin cytoskeleton. In nocodazole-treated cells, the three-dimensional organization of cortical actin filaments appeared less ordered than in controls. Measurements with fluorescence-detected linear dichroism indicated a decrease in the alignment of filaments along the spindle axis. In contrast, actin filaments in taxol-treated cells showed an increased alignment along the equator on both the ventral and dorsal cortical surfaces, mirroring the redistribution pattern of surface receptors. Together, these experiments show that spindle microtubules are involved in directing bipolar flow of surface receptors and reorganization of actin filaments during cell division, thus acting as a stimulus for positioning cortical cytoskeletal components and organizing the contractile apparatus of dividing tissue culture cells.

Actins↗
PubMed1977

[Mechanisms of participation of the sensomotor cortex in controlling movements].

Neuromorphological, neurophysiological and biomechanical studies in cats revealed cortical structural neuronal modules and functional units of different grades of complexity. Single systemic principle was determined for the sensorimotor cortex activity: structurally organized neuronal modules, having distributed outputs, can be involved in different functional units for purposeful movements. Specific lemniscal signals concerning the movements are the factor which filters inflow of teleceptive information to the neuronal modules and determines exact torographical relations of cortical motor outputs.

Animals↗
PubMed1988

Distribution and some projections of cholinergic neurons in the brain of the common marmoset, Callithrix jacchus.

The distribution of choline acetyltransferase-immunoreactive (ChAT-IR) neurons was studied in the brain of the common marmoset by using immunohistochemistry. ChAT-IR neurons were found in the medial septal nucleus, vertical and horizontal limb nuclei of the diagonal band, the nucleus basalis of Meynert, pedunculopontine nucleus and laterodorsal tegmental nucleus, and also in the striatum, habenula, and brainstem cranial nerve motor nuclei. The organization of ChAT-IR neurons in the basal forebrain, midbrain, and pons is consistent with the Ch1-Ch6 nomenclature introduced by Mesulam et al. ('83). The combination of the retrograde transport of HRP-WGA with ChAT immunohistochemistry revealed the distribution of neurons in the Ch4 cell group projecting to the dorsolateral prefrontal cortex. The activity of ChAT was highest in limbic cortical structures, such as the hippocampus, and lowest in association areas of the neocortex. Lesions at various loci in the basal forebrain resulted in differential patterns of ChAT loss in the cortex, which suggests some degree of topographical organization of Ch4 projections to the cortical mantle.

Animals↗