SEARCH · PubMed Health

Results for “functional network connectivity”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 955 records · Page 53Linked to original sources

PubMed2001

Growth-stimulating pathways in lung cancer: implications for targets of therapy.

Growth-stimulating pathways activated independently of their normal tissue environment are critical to the carcinogenesis and progression of lung cancer. These pathways are comprised of extracellular growth factors; their specific receptors on the cellular membrane; signal transduction cascades in the cytosol; and target molecules, including cytoskeletal proteins, metabolic regulators, and transcription factors in the nucleus. Growth factors can be divided into two groups based on their receptors: G-protein-coupled receptors and receptor tyrosine kinases. Growth factors induce clonal expansion of lung cancer cells by autocrine and/or paracrine mechanisms. Signal transduction cascades form an extremely large and complicated network with cross-talk connections. Ras, phosphatidylinositol-3-OH kinase, and phospholipase C are three key regulators involved in the network. Recent progress in our understanding of the oncoproteins functioning in the pathways has led to the development of novel therapeutic agents. Some of the most exciting results have been obtained with inhibitors of receptor tyrosine kinases. Phase I studies of epidermal growth factor-receptor inhibitors demonstrate objective responses without severe toxicity as single agents in patients with non-small-cell lung cancer refractory to conventional chemotherapy. This new strategy might lead to breakthroughs in the treatment of lung cancer with distant metastases not curable by conventional chemotherapy alone.

Journal Article↗

PubMedDate not supplied

[Changes in synaptic potentials and axonal delays as factors causing epileptic instability of neuronal networks].

Synaptic weights, axonal delays and excitability thresholds are three basic parameters influencing the function of neuronal network as a dynamic system. Changes of the general level of the signal flow, without changes in relation between excitatory and inhibitory connections can cause pathologic oscillations in the network. The conductivity in neuronal nets depends on electrochemical processes and may be influenced by the pH-status, ion concentrations, among other parameters. Also different pathological processes can change it. Even slight changes of axonal delays, as shown above, can cause in certain situations unstable, epileptic oscillations of the net.

Action Potentials↗

PubMed1979

[Histochemical and cytologic changes in the liver in experimental poisoning and subsequent pregnancy].

In 275 white rats chronic intoxication was produced by injection of amidopyrine acetaldehyde and chloraldehyde derivatives for 4 months. Histochemical and electron microscopic investigations of the liver under the experimental conditions and subsequent pregnancy revealed certain changes in nucleic metabolism, glycogenolisis, in the content of sulfhydryl, disulfide, carboxylic groups of protein molecules. Decrease in activity of enzymes of Krebs cycle and pentosophosphate cycle proved the deep changes in hepatocytes at the level of oxidation-reduction processes and protein synthesis. Ultramicroscopic changes in the nucleus, in cytoplasmic network, mitochondria and local degenerative alterations determined the level of morphologic reconstructions in connection with the intoxication. As the liver performs a number of vital functions and is closely connected with regulatory systems of the organism, morphofunctional shifts in the organ affect unfavourably the system mother--fetus.

Acetaldehyde↗

PubMed1976

Human skin burns induced by defibrillator default current.

The attachment of various types of electronic instrumentation to a patient can lead to hazardous interactions. Component malfunction in a single piece of equipment connected to a patient may be totally innocuous. However, the same fault occurring in an identical piece of equipment functioning as one component in a network of monitoring and electrosurgical equipment can result in severe burns or even electrocution. This paper describes interaction between a defective defibrillator paddle and an electrosurgical unit. Burns and ventricular fibrillation resulting from this malfunction and interaction are described in detail and the electrical circuits are analyzed.

Burns, Electric↗

PubMed1998

Neuronal circuitry and synaptic connectivity of the basal ganglia.

The concept of organization of the basal ganglia has changed markedly over the last 10 years. These developments have led to the introduction of a schematic model of the functional circuitry of the basal ganglia that accounts for normal and abnormal basal ganglia functions. The recent introduction of powerful techniques for the analysis of neuronal networks has led to many new developments in our understanding of the anatomic and synaptic organization of the basal ganglia. The objective of this article is to go from the established model of the basal ganglia connectivity to new anatomic findings that lead to reconsideration and refinement of some aspects of the models.

Basal Ganglia↗

PubMed2004

A new approach to the extraction of ANN rules and to their generalization capacity through GP.

Various techniques for the extraction of ANN rules have been used, but most of them have focused on certain types of networks and their training. There are very few methods that deal with ANN rule extraction as systems that are independent of their architecture, training, and internal distribution of weights, connections, and activation functions. This article proposes a methodology for the extraction of ANN rules, regardless of their architecture, and based on genetic programming. The strategy is based on the previous algorithm and aims at achieving the generalization capacity that is characteristic of ANNs by means of symbolic rules that are understandable to human beings.

Algorithms↗

PubMed2001

Can meaningful effective connectivities be obtained between auditory cortical regions?

Structural equation modeling (SEM) of neuroimaging data can be evaluated both for the goodness of fit of the model and for the strength of path coefficients (as an index of effective connectivity). SEM of auditory fMRI data is made difficult by the necessary sparse temporal sampling of the time series (to avoid contamination of auditory activation by the response to scanner noise) and by the paucity of well-defined anatomical information to constrain the functional model. We used SEM (i.e., a model incorporating latent variables) to investigate how well fMRI data in four adjacent cortical fields can be described as an auditory network. Seven of the 14 models (2 hemispheres x (6 subjects and 1 group)) produced a plausible description of the measured data. Since the auditory model to be tested is not fully validated by anatomical data, our approach requires that goodness of fit be confirmed to ensure generalizability of connectivity patterns. For good-fitting models, connectivity patterns varied significantly across subjects and were not replicable across stimulus conditions. SEM of central auditory function therefore appears to be highly sensitive to the voxel-selection procedure and/or the sampling of the time series.

Adult↗

PubMed2003

Visualisation and graph-theoretic analysis of a large-scale protein structural interactome.

BACKGROUND: Large-scale protein interaction maps provide a new, global perspective with which to analyse protein function. PSIMAP, the Protein Structural Interactome Map, is a database of all the structurally observed interactions between superfamilies of protein domains with known three-dimensional structure in the PDB. PSIMAP incorporates both functional and evolutionary information into a single network. RESULTS: We present a global analysis of PSIMAP using several distinct network measures relating to centrality, interactivity, fault-tolerance, and taxonomic diversity. We found the following results: Centrality: we show that the center and barycenter of PSIMAP do not coincide, and that the superfamilies forming the barycenter relate to very general functions, while those constituting the center relate to enzymatic activity. Interactivity: we identify the P-loop and immunoglobulin superfamilies as the most highly interactive. We successfully use connectivity and cluster index, which characterise the connectivity of a superfamily's neighbourhood, to discover superfamilies of complex I and II. This is particularly significant as the structure of complex I is not yet solved. Taxonomic diversity: we found that highly interactive superfamilies are in general taxonomically very diverse and are thus amongst the oldest. Fault-tolerance: we found that the network is very robust as for the majority of superfamilies removal from the network will not break up the network. CONCLUSIONS: Overall, we can single out the P-loop containing nucleotide triphosphate hydrolases superfamily as it is the most highly connected and has the highest taxonomic diversity. In addition, this superfamily has the highest interaction rank, is the barycenter of the network (it has the shortest average path to every other superfamily in the network), and is an articulation vertex, whose removal will disconnect the network. More generally, we conclude that the graph-theoretic and taxonomic analysis of PSIMAP is an important step towards the understanding of protein function and could be an important tool for tracing the evolution of life at the molecular level.

Archaeal Proteins↗

PubMed2026

Optimizing eco-engineering pedogenesis of bauxite residues: Synergistic effects of humus and FeSO4/sulfur on microbial community and function.

Eco-engineered pedogenesis represents a promising approach for soil amelioration of bauxite residues (BRs) through exogenous organic matter. However, the role of humus in mediating this process remains poorly understood, significantly impeding the eco-engineering rehabilitation of BRs. In this study, we conducted pot experiments and subsequent microbial analysis to evaluate the individual improvement of humic acid (HA), fulvic acid (FA), and corn straw (SWZ) on the BRs' pedogenesis. High-throughput sequencing analysis revealed that both FA and SWZ were more effective than HA in steering microbial community assembly, as community diversity, dominant taxa enrichment, and species' interaction were all significantly higher (p < 0.05) in the FA/SWZ treatments than in HA treatments. Notably, the combination of FA with FeSO4 specifically enriched halophilic taxa, while FA coupled with sulfur (S) significantly improved the connectivity and complexity of the microbial network, as the average connection degree increasing from 1.008 to 1.113. Hydrolytic enzyme activity assays further indicated that FA, especially when combined with S, was the most effective treatment in restoring microbial function during BR pedogenesis. These findings highlight FA as a critical driver of microbial restructuring and functional recovery in BRs. Moreover, its efficacy can be enhanced by co-amendment with FeSO4 or S. This study provides important theoretical and practical insights for optimizing organic-inorganic amendment strategies to accelerate the eco-engineering pedogenesis of bauxite residues.

Humic Substances↗

PubMed1993

An n-level field theory of biological neural networks.

An n-level field theory, based on the concept of "functional interaction", is proposed for a description of the continuous dynamics of biological neural networks. A "functional interaction" describes the action from one substructure of a network to another at several levels of organization, molecular, synaptic, and neural. Because of the continuous representation of neurons and synapses, which constitute a hierarchical system, it is shown that the property of non-locality leads to a non-local field operator in the field equations. In a hierarchical continuous system, the finite velocity of the functional interaction at the lower level implies non-locality at the higher level. Two other properties of the functional interaction are introduced in the formulation: the non-symmetry between sources and sinks, and the non-uniformity of the medium. Thus, it is shown that: (i) The coupling between topology and geometry can be introduced via two functions, the density of neurons at the neuronal level of organization, and the density-connectivity of synapses between two points of the neural space at the synaptic level of organization. With densities chosen as Dirac functions at regularly spaced points, the dynamics of a discrete network becomes a particular case of the n-level field theory. (ii) The dynamics at each of the molecular and synaptic lower level are introduced, at the next upper level, both in the source and in the non-local interaction of the field to integrate the dynamics at the neural level. (iii) New learning rules are deduced from the structure of the field equations: Hebbian rules result from strictly local activation; non-Hebbian rules result from homosynaptic activation with strict heterosynaptic effects, i.e., when an activated synaptic pathway affects the efficacy of a non-activated one; non-Hebbian rules and/or non-linearities result from the structure of the interaction operator and/or the internal biochemical kinetics.

Animals↗

PubMed2005

Behavioral evidence that segregation and representation are dissociable hippocampal functions.

Hippocampal activity is thought to encode spatial representations in a distributed associative network. This idea predicts that partial hippocampal lesions would spare acquisition and impair retrieval of a place response as long as enough connections remained intact to encode associations. Water maze experiments supported the predictions, but the prediction of impaired retrieval was not supported when tetrodotoxin (TTX) was injected into one hippocampus and rats were tested in a place avoidance task on a rotating arena with shallow water. The rotation dissociated relevant distal stimuli from irrelevant self-motion stimuli. To explain the discrepancy, we hypothesized that the segregation of relevant and irrelevant stimuli and stimuli association into representations are distinct hippocampus-dependent operations, and whereas associative representation is more sensitive to disruption during retrieval than learning, stimulus segregation is more sensitive to disruption during learning than during retrieval. The following predictions were tested: (1) the TTX injection would spare learning but (2) impair retrieval of a place response in the water maze, which has a high associative representational demand but a low demand for segregation; (3) the injection would impair learning but (4) spare retrieval of place avoidance in the rotating arena filled with water, which has a high demand for stimulus segregation but a low associative representational demand. All four predictions were confirmed. The hypothesis also explains the pattern of sparing and impairment after the TTX injection in other place avoidance task variants, leading us to conclude that stimulus separation and association representation are dissociable functions of the hippocampus.

Analysis of Variance↗

PubMedDate not supplied

Models of Hopfield-type quaternion neural networks and their energy functions.

Recently models of neural networks that can directly deal with complex numbers, complex-valued neural networks, have been proposed and several studies on their abilities of information processing have been done. Furthermore models of neural networks that can deal with quaternion numbers, which is the extension of complex numbers, have also been proposed. However they are all multilayer quaternion neural networks. This paper proposes models of fully connected recurrent quaternion neural networks, Hopfield-type quaternion neural networks. Since quaternion numbers are non-commutative on multiplication, some different models can be considered. We investigate dynamics of these proposed models from the point of view of the existence of an energy function and derive their conditions for existence.

Algorithms↗

PubMed2005

Stress and the gastrointestinal tract.

Stress, defined as an acute threat to homeostasis, evokes an adaptive or allostatic response and can have both a short- and long-term influence on the function of the gastrointestinal tract. The enteric nervous system is connected bidirectionally to the brain by parasympathetic and sympathetic pathways forming the brain-gut axis. The neural network of the brain, which generates the stress response, is called the central stress circuitry and includes the paraventricular nucleus of the hypothalamus, amygdala and periaqueductal gray. It receives input from the somatic and visceral afferent pathways and also from the visceral motor cortex including the medial prefrontal, anterior cingulate and insular cortex. The output of this central stress circuit is called the emotional motor system and includes automatic efferents, the hypothalamus-pituitary-adrenal axis and pain modulatory systems. Severe or long-term stress can induce long-term alteration in the stress response (plasticity). Corticotropin releasing factor (CRF) is a key mediator of the central stress response. Two CRF receptor subtypes, R1 and R2, have been described. They mediate increased colonic motor activity and slowed gastric emptying, respectively, in response to stress. Specific CRF receptor antagonists injected into the 0 block these visceral manifestations of stress. Circulating glucocorticoids exert an inhibitory effect on the stress response by receptors located in the medial prefrontal cortex and hippocampus. Many other neurotransmitters and neuroimmunomodulators are being evaluated. Stress increases the intestinal permeability to large antigenic molecules. It can lead to mast cell activation, degranulation and colonic mucin depletion. A reversal of small bowel water and electrolyte absorption occurs in response to stress and is mediated cholinergically. Stress also leads to increased susceptibility to colonic inflammation, which can be adaptively transferred among rats by sensitized CD4(+) lymphocytes. The association between stress and various gastrointestinal diseases, including functional bowel disorders, inflammatory bowel disease, peptic ulcer disease and gastroesophageal reflux disease, is being actively investigated. Attention to the close relation between the brain and gut has opened many therapeutic avenues for the future.

Adaptation, Psychological↗

PubMed2001

Bulbus arteriosus of the bivalve mollusc Mercenaria mercenaria: Morphology and pharmacology.

We examined the morphology and pharmacology of the bulbus arteriosus of the marine bivalve mollusc Mercenaria mercenaria. The bulbus arteriosus is an organ of unknown function associated with the posterior aorta and the ventricle. It is composed of connective tissue interspersed with muscle bundles. In contrast to the lumen of the ventricle, which has an extensive trabecular network, the lumen of the bulbus arteriosus has no trabeculae. No valve is present in the posterior aorta connecting the lumina of the ventricle and the bulbus arteriosus. Scattered neuronal profiles are present in the wall and the axonal processes contain vesicles that may contain neurosecretory products. We did not, however, find synapses or evidence of vesicular release into the lumen of the bulbus arteriosus. The bulbus arteriosus contains acetylcholine, 5-hydroxytryptamine (5HT), and the molluscan neuropeptides FMRFamide (phenyl-alanyl-methionyl-arginyl-phenylalaninylamide) and FLRFamide (phenylalanyl-leucinyl-arginyl-phenylalanylamide). The isolated bulbus arteriosus contracts tonically in response to mechanical stress and exposure to 5HT or FMRFamide, while acetylcholine relaxes it. We surmise that the bulbus arteriosus probably functions as a mechanism for regulating the relative amounts of hemolymph pumped into the anterior and posterior aortae by the ventricle and that the bulbus arteriosus may be a neurohemal site.

Acetylcholine↗

PubMed2006

Mechanical tension and integrin alpha 2 beta 1 regulate fibroblast functions.

The extracellular matrix (ECM) environment in connective tissues provides fibroblasts with a structural scaffold and modulates cell shape, but it also profoundly influences the fibroblast phenotype. Here we studied fibroblasts cultured in a three-dimensional network of native collagen, which was either mechanically stressed or relaxed. Mechanical load induces fibroblasts that synthesize abundant ECM and a characteristic array of cytokines/chemokines. This phenotype is reminiscent of late granulation tissue or scleroderma fibroblasts. By contrast, relaxed fibroblasts are characterized by induction of proteases and a subset of cytokines that does not overlap with that of mechanically stimulated cells. Thus, the biochemical composition and physical nature of the ECM exert powerful control over the phenotypes of fibroblasts, ranging from "synthetic" to "inflammatory" phenotypes. Interactions between fibroblasts and collagen fibrils are mostly mediated by a subset of beta 1 integrin receptors. Fibroblasts utilize alpha 1 beta 1, alpha 2 beta 1, and alpha 11 beta 1 integrins for establishing collagen contacts and transducing signals. In vitro assays and mouse genetics have demonstrated individual tasks served by each receptor, but also functional redundancy. Unraveling the integrated functions of fibroblasts, collagen integrin receptors, collagen fibrils, and mechanical tension will be important to understand the molecular mechanisms underlying tissue repair and fibrosis.

Animals↗

PubMedDate not supplied

Deterministic dynamics emerging from a cortical functional architecture.

Cerebral cortex has a range of interconnected functional architectures. Some appear random and without structure, while others are geometrical. Although the biological details certainly constrain spatial temporal patterns in neural networks, the influence that the laws of deterministic dynamics bring to bear on even isolated simple geometries are unknown. Layer II/III of primary visual cortex has long range horizontal connections with projections to and from other layers. The long range excitatory connections were modeled in isolation as an isolated laterally connected functional architecture. The Hodgkin-Huxley or Pinsky-Rinzel equations were used to simulate the neuronal elements. Waves of activity could propagate through the functional architecture; depending on the synaptic kinetics, the system could settle down into quiescence, oscillations, or seemingly random behavior. Order could be found in random-looking behavior by the application of techniques from chaos theory. Furthermore, the range and transitions of the temporal patterns in the modeled collection of neurons are similar to those found in other non-linear systems. The possibility that the temporal patterns of neurons in situ are also constrained by these mathematical laws is discussed.

Action Potentials↗

PubMed2002

Four cases of desmosis coli: severe chronic constipation, massive dilatation of the colon, and hypoperistalsis due to of changes in the colonic connective-tissue net.

We present four patients 5, 10, 12, and 17 years of age, each with a long history of severe constipation and hypoperistalsis of the gut. Three had partial or total resection of the colon, all had enterostomies, and only one maintains normal bowel function after reanastomosis. We report the clinical courses, radiologic findings, and operative procedures for all four cases. Preoperative full-thickness biopsies and the resected colon specimens revealed a complete or incomplete lack of the mesh network of collagen. The connective-tissue layer between the circular and longitudinal muscles was missing. Contrary to expectations, the enteric nervous system (ENS) was normal or near-normal in the affected areas. Hypo- and dysganglionosis was found additionally in some proximal segments of colon and/or small bowel. This combination of clinical symptoms and pathological findings is called desmosis of the colon with reference to a working hypothesis in a preliminary report by Meier-Ruge in 1998. Aplastic or hypoplastic desmosis may be the reason for the disturbed gut motility. Histologic examination should thus not only exclude changes of the ENS.

Adolescent↗

PubMed1998

The connection between regularization operators and support vector kernels.

In this paper a correspondence is derived between regularization operators used in regularization networks and support vector kernels. We prove that the Green's Functions associated with regularization operators are suitable support vector kernels with equivalent regularization properties. Moreover, the paper provides an analysis of currently used support vector kernels in the view of regularization theory and corresponding operators associated with the classes of both polynomial kernels and translation invariant kernels. The latter are also analyzed on periodical domains. As a by-product we show that a large number of radial basis functions, namely conditionally positive definite functions, may be used as support vector kernels.

Journal Article↗