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Results for “functional network connectivity”

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At least 433 records · Page 24Linked to original sources

PubMed1993

Neural net pruning based on functional behavior of neurons.

This paper proposes a new pruning method based on merging neurons with similar functional behavior which is defined by the internal representations of each neuron for the entire training set. Classification of neurons by their functional behavior with respect to the input vectors provides a powerful tool for pruning neurons and connections, thus reducing the network complexity and increasing its generalization capability. The most remarkable property of this pruning scheme is its ability to preserve net functionality by transferring the role of every removed neuron to the most fitted neuron of the surviving ones, using a unique merging and compensation procedure. The implementation of the proposed method is demonstrated using a detailed numerical example and its performance is examined by a statistical measure calculated by repeating the training procedure several times. The influence of parameter selection on pruning performance and generalization ability is discussed and demonstrated by examining statistical results.

Animals↗

PubMed1996

Suppression of synaptic transmission may allow combination of associative feedback and self-organizing feedforward connections in the neocortex.

Selective suppression of synaptic transmission during learning is proposed as a physiological mechanism for combining associative memory function at feedback synapses with self-organization of feedforward synapses in neocortical structures. A computational model demonstrates how selective suppression of feedback transmission allows this combination of synaptic function. During learning, sensory stimuli and the desired response are simultaneously presented as input to the network. Feedforward connections form self-organized representations of input, while suppressed feedback connections learn the transpose of the feedforward connectivity. During recall, suppression of transmission is removed, input activates the self-organized representation, and activity settles into a learned solution to the problem. This computational model can be used for learning of problems which are not linearly separable, including the negative patterning task (the XOR problem). Experiments in brain slice preparations of the rat somatosensory cortex tested whether the combination of self-organization and associative memory function could be provided by cholinergic suppression selective for feedback versus feedforward synapses. The cholinergic agonist carbachol selectively suppressed synaptic potentials elicited by stimulation of layer I (which contains a high percentage of feedback synapses), while having no effect on synaptic potentials elicited by stimulation of layer IV (with a high percentage of afferent and feedforward synapses).

Animals↗

PubMed2001

From topology to dynamics in biochemical networks.

Abstract formulations of the regulation of gene expression as random Boolean switching networks have been studied extensively over the past three decades. These models have been developed to make statistical predictions of the types of dynamics observed in biological networks based on network topology and interaction bias, p. For values of mean connectivity chosen to correspond to real biological networks, these models predict disordered dynamics. However, chaotic dynamics seems to be absent from the functioning of a normal cell. While these models use a fixed number of inputs for each element in the network, recent experimental evidence suggests that several biological networks have distributions in connectivity. We therefore study randomly constructed Boolean networks with distributions in the number of inputs, K, to each element. We study three distributions: delta function, Poisson, and power law (scale free). We analytically show that the critical value of the interaction bias parameter, p, above which steady state behavior is observed, is independent of the distribution in the limit of the number of elements N--> infinity. We also study these networks numerically. Using three different measures (types of attractors, fraction of elements that are active, and length of period), we show that finite, scale-free networks are more ordered than either the Poisson or delta function networks below the critical point. Thus the topology of scale-free biochemical networks, characterized by a wide distribution in the number of inputs per element, may provide a source of order in living cells. (c) 2001 American Institute of Physics.

Journal Article↗

PubMed2005

Measuring temporal dynamics of functional networks using phase spectrum of fMRI data.

We present a novel method to measure relative latencies between functionally connected regions using phase-delay of functional magnetic resonance imaging data. Derived from the phase component of coherency, this quantity estimates the linear delay between two time-series. In conjunction with coherence, derived from the magnitude component of coherency, phase-delay can be used to examine the temporal properties of functional networks. In this paper, we apply coherence and phase-delay methods to fMRI data in order to investigate dynamics of the motor network during task and rest periods. Using the supplementary motor area (SMA) as a reference region, we calculated relative latencies between the SMA and other regions within the motor network including the dorsal premotor cortex (PMd), primary motor cortex (M1), and posterior parietal cortex (PPC). During both the task and rest periods, we measured significant delays that were consistent across subjects. Specifically, we found significant delays between the SMA and the bilateral PMd, bilateral M1, and bilateral PPC during the task condition. During the rest condition, we found that the temporal dynamics of the network changed relative to the task period. No significant delays were measured between the SMA and the left PM and left M1; however, the right PM, right M1, and bilateral PPC were significantly delayed with respect to the SMA. Additionally, we observed significant map-wise differences in the dynamics of the network at task compared to the network at rest. These differences were observed in the interaction between the SMA and the left M1, left superior frontal gyrus, and left middle frontal gyrus. These temporal measurements are important in determining how regions within a network interact and provide valuable information about the sequence of cognitive processes within a network.

Adult↗

PubMed2005

Functional magnetic resonance imaging and multiple sclerosis: the evidence for neuronal plasticity.

Blood oxygen level-dependent (BOLD) functional magnetic resonance imaging (fMRI) has emerged as a powerful technique to visualize the localization of cerebral activity in both healthy and diseased brains. BOLD fMRI has been used to assess brain function in a variety of diseases, including multiple sclerosis (MS), and has shown that altered patterns of connectivity are used to recruit more widespread eloquent brain networks engaged in tasks relating to motor activity, sensory and cognitive function, and memory when compared to normal controls. This review will examine the evidence that functional reorganization is a consequence of demyelination and tissue loss in MS that may serve as an adaptive response to limit clinical disability. It remains unclear whether cerebral plasticity is a marker of permanent functional restructuring or a short-term compensatory response to injury. Long-term longitudinal studies that correlate fMRI activity with other MRI markers of disease burden and activity, as well as with clinical measures of disease activity and progression, are badly needed to determine fMRI's relevance to clinical practice and its place as a surrogate outcome measure in MS.

Brain↗

PubMed2006

A gene-centered C. elegans protein-DNA interaction network.

Transcription regulatory networks consist of physical and functional interactions between transcription factors (TFs) and their target genes. The systematic mapping of TF-target gene interactions has been pioneered in unicellular systems, using "TF-centered" methods (e.g., chromatin immunoprecipitation). However, metazoan systems are less amenable to such methods. Here, we used "gene-centered" high-throughput yeast one-hybrid (Y1H) assays to identify 283 interactions between 72 C. elegans digestive tract gene promoters and 117 proteins. The resulting protein-DNA interaction (PDI) network is highly connected and enriched for TFs that are expressed in the digestive tract. We provide functional annotations for approximately 10% of all worm TFs, many of which were previously uncharacterized, and find ten novel putative TFs, illustrating the power of a gene-centered approach. We provide additional in vivo evidence for multiple PDIs and illustrate how the PDI network provides insights into metazoan differential gene expression at a systems level.

Animals↗

PubMed2005

Computation of inverse functions in a model of cerebellar and reflex pathways allows to control a mobile mechanical segment.

The command and control of limb movements by the cerebellar and reflex pathways are modeled by means of a circuit whose structure is deduced from functional constraints. One constraint is that fast limb movements must be accurate although they cannot be continuously controlled in closed loop by use of sensory signals. Thus, the pathways which process the motor orders must contain approximate inverse functions of the bio-mechanical functions of the limb and of the muscles. This can be achieved by means of parallel feedback loops, whose pattern turns out to be comparable to the anatomy of the cerebellar pathways. They contain neural networks able to anticipate the motor consequences of the motor orders, modeled by artificial neural networks whose connectivity is similar to that of the cerebellar cortex. These networks learn the direct biomechanical functions of the limbs and muscles by means of a supervised learning process. Teaching signals calculated from motor errors are sent to the learning sites, as, in the cerebellum, complex spikes issued from the inferior olive are conveyed to the Purkinje cells by climbing fibers. Learning rules are deduced by a differential calculation, as classical gradient rules, and they account for the long term depression which takes place in the dendritic arborizations of the Purkinje cells. Another constraint is that reflexes must not impede voluntary movements while remaining at any instant ready to oppose perturbations. Therefore, efferent copies of the motor orders are sent to the interneurones of the reflexes, where they cancel the sensory-motor consequences of the voluntary movements. After learning, the model is able to drive accurately, both in velocity and position, angular movements of a rod actuated by two pneumatic McKibben muscles. Reflexes comparable to the myotatic and tendinous reflexes, and stabilizing reactions comparable to the cerebellar sensory-motor reactions, reduce efficiently the effects of perturbing torques. These results allow to link the behavioral concepts of the equilibrium-point "lambda model" [J Motor Behav 18 (1986) 17] with anatomical and physiological features: gains of reflexes and sensori-motor reactions set the slope of the "invariant characteristic," and efferent copies set the "threshold of the stretch reflex." Thus, mathematical and physical laws account for the raison d'etre of the inhibitory nature of Purkinje cells and for the conspicuous anatomical pattern of the cerebellar pathways. These properties of these pathways allow to perform approximate inverse calculations after learning of direct functions, and insure also the coordination of voluntary and reflex motor orders.

Algorithms↗

PubMed2006

Advances in autism neuroimaging research for the clinician and geneticist.

This review focuses on recent advances in the in vivo study of the whole brain in idiopathic autism. The brain is abnormally large in some but not all children with autism during post-natal development. Age-related changes in brain volume in autism are complex and appear to be abnormal from infancy into adulthood. Diffuse differences in total and regional gray and white matter volumes are found. The volumetric abnormalities appear to follow anomalous, complex, and non-uniform developmental curves. Diffuse abnormalities of brain chemical concentrations, neural network anatomy, brain lateralization, intra- and inter-hemispheric morphologic and functional connectivity, and serotonin synthesis capacity are also found. Abnormalities of head growth are first apparent during infancy. Abnormalities of total brain volume, gray and white matter volumes, brain chemistry, serotonin synthesis, and brain electrophysiology are evident by early childhood. Currently, no method of brain imaging helps with diagnosis or treatment of idiopathic autism, but ongoing research aims to unravel the heterogeneity of autism and may provide future diagnostic tools that inform treatment.

Autistic Disorder↗

PubMed1979

Transventricular blood vessels in the third ventricle of the armadillo brain.

Transventricular filaments were observed with scanning electron microscopy on the dorsolateral wall of the infundibular recess of the third ventricle of the armadillo brain. Two to seven transventricular filaments per animal were present in 6 of 18 animals. There were two types of transventricular filaments, ciliated and bare. Using transmission electron microscopy, we determined that these filaments consisted of a single, central capillary surrounded by ciliated ependymal cells and a small accumulation of axons in five animals. In one animal, a bare filament had a central capillary surrounded by a large accumulation of axons with no surrounding ependyma. The consistent location and structure of these filaments indicate a possible function for a small vascular network, as well as a possible commissural network connecting right and left hypothalami in the region of infundibular nuclei.

Animals↗

PubMed2002

Correspondence of event-related potential tomography and functional magnetic resonance imaging during language processing.

Combining event-related potentials (ERP) and functional magnetic resonance imaging (fMRI) may provide sufficient temporal and spatial resolution to clarify the functional connectivity of neural processes, provided both methods represent the same neural networks. The current study investigates the statistical correspondence of ERP tomography and fMRI within the common activity volume and time range in a complex visual language task. The results demonstrate that both methods represent similar neural networks within the bilateral occipital gyrus, lingual gyrus, precuneus and middle frontal gyrus, and the left inferior and superior parietal lobe, middle and superior temporal gyrus, cingulate gyrus, superior frontal gyrus and precentral gyrus. The mean correspondence of both methods over subjects was significant. On an individual basis, only half of the subjects showed significantly corresponding activity patterns, suggesting that a one-to-one correspondence between individual fMRI activation patterns and ERP source tomographies integrated over microstates cannot be assumed in all cases.

Adult↗

PubMed2002

Generalization of single immunological experiences by idiotypically mediated clonal connections.

Clonal interactions of B cells by idiotope-specific mutual recognition of their antigen receptors with the participation of T cells were assumed to form a web of unknown density, referred to as the idiotypic network. Although these clonal connections were proposed to fulfill important internal regulatory functions, their biological significance, especially in relation to antigen-induced immune responses, remained a mystery. In view of this, we postulate that the basic function of the idiotypic internal connection between B and T cell antigen receptors is to transform antigen-induced cellular activations, by idiotypic crossreactivity, into the regulation of cell clones with different antigen specificities. This process leads not only to the suppression of major clones but also to the activation of minor ones. The latter activating property may allow the generalization of single antigenic experiences, so that the immune system in its entirety benefits in its battle against environmental microbes. Such idiotypic clonal interactions are particularly effective in early ontogeny. During a short neonatal imprinting period, maternal immunological knowledge in the form of somatically mutated, high-affinity IgG antibodies, acquired through a continuous encounter with external antigens, guides the initial ontogenetic development of the immune system and so exerts long-lasting transgenerational advantageous effects in the offspring.

Animals↗

PubMed2006

Detecting functional modules in the yeast protein-protein interaction network.

MOTIVATION: Identification of functional modules in protein interaction networks is a first step in understanding the organization and dynamics of cell functions. To ensure that the identified modules are biologically meaningful, network-partitioning algorithms should take into account not only topological features but also functional relationships, and identified modules should be rigorously validated. RESULTS: In this study we first integrate proteomics and microarray datasets and represent the yeast protein-protein interaction network as a weighted graph. We then extend a betweenness-based partition algorithm, and use it to identify 266 functional modules in the yeast proteome network. For validation we show that the functional modules are indeed densely connected subgraphs. In addition, genes in the same functional module confer a similar phenotype. Furthermore, known protein complexes are largely contained in the functional modules in their entirety. We also analyze an example of a functional module and show that functional modules can be useful for gene annotation. CONTACT: yuan.33@osu.edu SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Algorithms↗

PubMed2005

Birdcage model for the Chinese meridian system: part VI. meridians as the primary regulatory system.

It is imperative to define the fundamental concepts of Qi, channels, and the meridian system of Chinese medicine in terms of scientific terminology before any meaningful and mutually beneficial dialog can begin between Chinese and Western medicine. In the Chinese theory, the meridian system as a whole is the system of the body. We propose the existence of a meridian regulatory system that governs interactions between and adjusts functions of internal organs, connects them to the body surface through a network of pathways (channels) and displays their status on the skin. The meridian systems is analyzed as a 28-leg, uniform, low pass birdcage coil, where each leg represents a channel. The channel is analyzed as a transmission line and Qi is the standing wave riding on it. Each segment in the channel is represented as a section of the transmission line and it is in natural oscillation, with its second lowest resonant frequency being the 50-round circulation frequency f50, 0.578 x 10(-3) Hz.

Acupuncture↗

PubMed2001

Feature selectivity and interneuronal cooperation in the thalamocortical system.

Action potentials are a universal currency for fast information transfer in the nervous system, yet few studies address how some spikes carry more information than others. We focused on the transformation of sensory representations in the lemniscal (high-fidelity) auditory thalamocortical network. While stimulating with a complex sound, we recorded simultaneously from functionally connected cell pairs in the ventral medial geniculate body and primary auditory cortex. Thalamic action potentials that immediately preceded or potentially caused a cortical spike were more selective than the average thalamic spike for spectrotemporal stimulus features. This net improvement of thalamic signaling indicates that for some thalamic cells, spikes are not propagated through cortex independently but interact with other inputs onto the same target cell. We then developed a method to identify the spectrotemporal nature of these interactions and found that they could be cooperative or antagonistic to the average receptive field of the thalamic cell. The degree of cooperativity with the thalamic cell determined the increase in feature selectivity for potentially causal thalamic spikes. We therefore show how some thalamic spikes carry more receptive field information than average and how other inputs cooperate to constrain the information communicated through a cortical cell.

Acoustic Stimulation↗

PubMed1984

Localization of type V collagen and type IV collagen in human cornea, lung, and skin. Immunohistochemical evidence by anti-collagen antibodies characterized by immunoelectroblotting.

Tissue distribution of Type V collagen in comparison with Type IV collagen was investigated by indirect immunofluorescence microscopy. Affinity-purified rat antibodies to Type IV and Type V collagens obtained from human placenta reacted specifically only with the corresponding type of collagen in both native and denatured conformations. In indirect immunofluorescent stainings of human skin, lung, and cornea tissues, Type IV and Type V collagens showed distinct distributions. Type IV collagen was distributed exclusively in basement membrane. However, Type V collagen had two characteristic features; a diffuse distribution in interstitium and the locations on or adjacent to basement membrane. On the basis of these findings and of biochemical characterization of the collagens, it is postulated that Type V collagen is an intermediate collagen, possibly having a function of binding or connecting of interstitial collagen fibrils with membranous collagen networks.

Adult↗

PubMed1998

[Features of the structure and parameters of the intra-alveolar septa in residents of Western Siberia].

In inhabitants of Novosibirsk and Moscow district intraalveolar septum, the basic functional element of the lung consists of interstitial connective tissue and capillar network, limited with basement membranes, on which cells of epithelial lining are placed. There are no principal differences in septal structure between individuals from both regions. The majority of morphometric parameters are statistically similar, although certain peculiarities were noted in human subjects from Siberia, the most important of which is that air-blood barrier in them is 33% thinner than those in inhabitants of Moscow district. Majority of capillaries possess the air-blood barrier from both sides. This increases diffous capacity of the lungs and blood oxygenation level.

Adult↗

PubMed2005

Revealing the large-scale network organization of growth hormone-secreting cells.

Pituitary growth hormone (GH)-secreting cells regulate growth and metabolism in animals and humans. To secrete highly ordered GH pulses (up to 1,000-fold rise in hormone levels in vivo), the pituitary GH cell population needs to mount coordinated responses to GH secretagogues, yet GH cells display an apparently heterogeneous scattered distribution in 2D histological studies. To address this paradox, we analyzed in 3D both positioning and signaling of GH cells using reconstructive, two-photon excitation microscopy to image the entire pituitary in GH-EGFP transgenic mice. Our results unveiled a homologous continuum of GH cells connected by adherens junctions that wired the whole gland and exhibited the three primary features of biological networks: robustness of architecture across lifespan, modularity correlated with pituitary GH contents and body growth, and connectivity with spatially stereotyped motifs of cell synchronization coordinating cell activity. These findings change our view of GH cells, from a collection of dispersed cells to a geometrically connected homotypic network of cells whose local morphology and connectivity can vary, to alter the timing of cellular responses to promote more coordinated pulsatile secretion. This large-scale 3D view of cell functioning provides a powerful approach to identify and understand other networks of endocrine cells that are thought to be scattered in situ. Many dispersed endocrine systems exhibit pulsatile outputs. We suggest that cell positioning and associated cell-cell connection mechanisms will be critical parameters that determine how well such systems can deliver a coordinated secretory pulse of hormone to their target tissues.

Animals↗

PubMedDate not supplied

Micropatterned substrates for the growth of functional neuronal networks of defined geometry.

The in vitro assembly of neuronal networks with control over cell position and connectivity is a fascinating approach not only for topics in basic neuroscience research but also in diverse applications such as biosensors and tissue engineering. We grew rat embryonic cortical neurons on patterned substrates created by microcontact printing. Polystyrene was used as a cell repellent background, onto which a grid pattern of physiological proteins was applied. We printed laminin and a mixture of extracellular matrix proteins and additionally both systems mixed with polylysine. Attachment of cells to the pattern with high fidelity as well as the formation of chemical synapses between neighboring cells on the pattern could be observed in all four cases, but cell attachment was strongly increased on samples containing polylysine. Neurons grown on patterned substrates had a membrane capacity smaller than that of neurons on homogeneously coated controls, which we attributed to the geometrical restrictions, but did not differ either in resting membrane potential or in the quality of synapses they formed. We therefore believe that the cells attach and differentiate normally on the pattern and form functional, mature synapses following the predefined geometry.

Action Potentials↗