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Results for “functional network connectivity”

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At least 397 records · Page 22Linked to original sources

PubMed2002

Disruption of coherent oscillations in inhibitory networks with anesthetics: role of GABA(A) receptor desensitization.

The effect of anesthetic drugs at central synapses can be described quantitatively by developing kinetic models of ligand-gated ion channels. Experiments have shown that the hypnotic propofol and the sedative benzodiazepine midazolam have similar effects on single inhibitory postsynaptic potentials (IPSPs) but very different effects on slow desensitization that are not revealed by examining single responses. Synchronous oscillatory activity in networks of interneurons connected by inhibitory synapses has been implicated in many hippocampal functions, and differences in the kinetics of the GABAergic response observed with anesthetics can affect this activity. Thus we have examined the effect of propofol and midazolam-enhanced IPSPs using mathematical models of self-inhibited one- and two-cell inhibitory networks. A detailed kinetic model of the GABA(A) channel incorporating receptor desensitization is used at synapses in our models. The most dramatic effect of propofol is the modulation of slow desensitization. This is only revealed when the network is driven at frequencies that are thought to be relevant to cognitive tasks performed in the hippocampus. The level of desensitization at synapses with propofol is significantly reduced compared to control synapses. In contrast, midazolam increases macroscopic desensitization at network synapses by altering receptor affinity without concurrently modifying desensitization rates. These differences in gating between the two drugs are shown to alter network activity in stereotypically different ways. Specifically, propofol dramatically increases the amount of excitatory drive necessary for synchronized behavior relative to control, which is not the case for midazolam. Moreover, the range of parameters for which synchrony occurs is larger for propofol but smaller for midazolam, relative to control. This is an important first step in linking alterations in channel kinetics with behavioral changes.

Algorithms↗

PubMed2003

Protein complexes and functional modules in molecular networks.

Proteins, nucleic acids, and small molecules form a dense network of molecular interactions in a cell. Molecules are nodes of this network, and the interactions between them are edges. The architecture of molecular networks can reveal important principles of cellular organization and function, similarly to the way that protein structure tells us about the function and organization of a protein. Computational analysis of molecular networks has been primarily concerned with node degree [Wagner, A. & Fell, D. A. (2001) Proc. R. Soc. London Ser. B 268, 1803-1810; Jeong, H., Tombor, B., Albert, R., Oltvai, Z. N. & Barabasi, A. L. (2000) Nature 407, 651-654] or degree correlation [Maslov, S. & Sneppen, K. (2002) Science 296, 910-913], and hence focused on single/two-body properties of these networks. Here, by analyzing the multibody structure of the network of protein-protein interactions, we discovered molecular modules that are densely connected within themselves but sparsely connected with the rest of the network. Comparison with experimental data and functional annotation of genes showed two types of modules: (i) protein complexes (splicing machinery, transcription factors, etc.) and (ii) dynamic functional units (signaling cascades, cell-cycle regulation, etc.). Discovered modules are highly statistically significant, as is evident from comparison with random graphs, and are robust to noise in the data. Our results provide strong support for the network modularity principle introduced by Hartwell et al. [Hartwell, L. H., Hopfield, J. J., Leibler, S. & Murray, A. W. (1999) Nature 402, C47-C52], suggesting that found modules constitute the "building blocks" of molecular networks.

Biophysical Phenomena↗

PubMed2006

Functional maturation of adult-generated granule cells.

The excitability and connectivity of adult-generated granule cells dictate to what extent newborn neurons participate in the hippocampal network. These functional parameters evolve as newborn cells mature and interact with the existing circuit. The progression of granule cell maturation during neonatal development appears to be reiterated in the adult, but with some caveats. New approaches to identify and track newborn neurons are revealing the timing of this process, as well as its sensitivity to activity-dependent regulation.

Aging↗

PubMed2006

Effective connectivity within the distributed cortical network for face perception.

Face perception elicits activation within a distributed cortical network in the human brain. The network includes visual ("core") regions, as well as limbic and prefrontal ("extended") regions, which process invariant facial features and changeable aspects of faces, respectively. We used functional Magnetic Resonance Imaging and Dynamic Causal Modeling to investigate effective connectivity and functional organization between and within the core and the extended systems. We predicted a ventral rather than dorsal connection between the core and the extended systems during face viewing and tested whether valence and fame would alter functional coupling within the network. We found that the core system is hierarchically organized in a predominantly feed-forward fashion, and that the fusiform gyrus (FG) exerts the dominant influence on the extended system. Moreover, emotional faces increased the coupling between the FG and the amygdala, whereas famous faces increased the coupling between the FG and the orbitofrontal cortex. Our results demonstrate content-specific dynamic alterations in the functional coupling between visual-limbic and visual-prefrontal face-responsive pathways.

Adult↗

PubMed2005

Multiple death pathways in retina-derived 661W cells following growth factor deprivation: crosstalk between caspases and calpains.

During development of the mammalian retina, neurons that do not succeed in establishing functional synaptic connections are eliminated by apoptosis, allowing the formation of a finely tuned network. Growth factors play a crucial role in controlling the balance between apoptosis and survival signals not only at developmental stages but also in long-term preservation of retinal functions. In the present work, we explore the apoptotic mechanisms triggered by growth factor deprivation of retina-derived 661W cells. Under serum starvation conditions, these cone photoreceptors underwent cell death with participation of caspase-9, -3 and -12. Interestingly, inhibition of caspases did not prevent apoptosis but only resulted in a temporary delay. We show m-calpain activation in parallel with caspases, indicating that more than one execution pathway is available to cone photoreceptors. Moreover, crosstalk of the caspase and calpain pathways was detected, suggesting a loop that may act to amplify the apoptotic cascade.

Animals↗

PubMed1991

Ultrastructural cytochemistry of anchoring filaments of human lymphatic capillaries and their relation to elastic fibers.

In previous studies "anchoring filaments" of human lymphatic capillaries have been shown to consist of microfibrils having histochemical and ultrastructural characteristics similar to elastin-associated microfibrils. When not associated with an elastin component, these microfibrils are referred to as "oxytalan microfibrils." In this study, alpha-glycol-containing carbohydrates and glycoconjugated sulfate groups, originating from sulphydryls and/or disulfide bridges, have been detected in anchoring filament microfibrils of human lymphatic capillaries by Thiery reaction (PA-TCH-SP) and "Hight Iron Diamine" cytochemical method (HID), respectively. Both of these chemical groups belong to the putative glycoprotein of which the microfibrils are constituted. Similar molecular characteristics have been demonstrated in elastic fiber microfibrils and oxytalan microfibrils of connective tissue. These findings suggest a close molecular similarity among these different types of microfibrils. Thus, whatever their individual location or denomination (anchoring filaments, oxytalan fibers, or elastin-associated microfibrils), these microfibrils form an uniform population of fibrous elements. These findings further support a structural (and functional) continuity between the lymphatic capillary wall and the elastic network of adjacent connective tissues previously described and termed "Fibrillar Elastic Apparatus" (FEA). Of interest, endothelial cells also selectively react positively to the PA-TCH-SP and HID methods.

Actin Cytoskeleton↗

PubMed2004

Integrating databases and expert systems for the analysis of brain structures: connections, similarities, and homologies.

The NeuroHomology Database system (NHDB) combines databases related to brain structures from different species with different knowledge management systems (KMSs) for systematization, evaluation and processing neurobiological data. Special attention is assessment of similarity of data from different species as a basis for exploring neural homologies. NHDB includes modules that handle brain structure and connectivity data, as well as inference engines for evaluation of the stored neurobiological information. The spatial inference engine evaluates the possible topological relations between cortical structures in different neuroanatomical atlases. The connectivity inference engine evaluates the reliability of information pertaining to fiber tracts as those are reflected in the literature. The inference engine for translation of neuroanatomical connections in different atlases evaluates the probability of existence of connections of interest in different parcellation schemes. Finally, the similarity inference engine calculates the overall degree of similarity of pairs of brain structures from different species by taking into account a set of eight criteria. We present examples of search for information in NHDB system, inferences of relations between cortical structures from equivalent neuroanatomical atlases, reconstruction of functional networks of brain structures from data collated from the literature, translation of connectivity matrices in equivalent parcellation schemes, and evaluations of similarities of brain structures from humans, macaques and rats.

Algorithms↗

PubMed2006

Functional connectivity of the fusiform gyrus during a face-matching task in subjects with mild cognitive impairment.

Cognitive function requires a high level of functional interaction between regions of a network supporting cognition. Assuming that brain activation changes denote an advanced state of disease progression, changes in functional connectivity may precede changes in brain activation. The objective of this study was to investigate changes in functional connectivity of the right middle fusiform gyrus (FG) in subjects with mild cognitive impairment (MCI) during performance of a face-matching task. The right middle FG is a key area for processing face stimuli. Brain activity was measured using functional MRI. There were 16 MCI subjects and 19 age-matched healthy controls. The linear correlation coefficient was utilized as a measure of functional connectivity between the right middle FG and all other voxels in the brain. There were no statistical differences found in task performance or activation between groups. The right middle FG of the healthy control and MCI groups showed strong bilateral positive linear correlation with the visual cortex, inferior and superior parietal lobules, dorsolateral prefrontal cortex (DLPFC) and anterior cingulate. The healthy controls showed higher positive linear correlation of the right middle FG to the visual cortex, parietal lobes and right DLPFC than the MCI group, whereas the latter had higher positive linear correlation in the left cuneus. In the healthy controls, the right middle FG had negative linear correlation with right medial frontal gyrus and superior temporal gyrus and with left inferior parietal lobule (IPL), angular gyrus, superior frontal gyrus and anterior cingulate gyrus, but the MCI group had negative linear correlation with the left IPL, angular gyrus, precuneus, anterior cingulate, and to right middle temporal gyrus and posterior cingulate gyrus. In the negatively linearly correlated regions, the MCI group had reduced functional connectivity to the frontal areas, right superior temporal gyrus and left IPL. Different regions of the cuneus and IPL had increased functional connectivity in either group. The putative presence of Alzheimer's disease neuropathology in MCI affects functional connectivity from the right middle FG to the visual areas and medial frontal areas. In addition, higher linear correlation in the MCI group in the parietal lobe may indicate the initial appearance of compensatory processes. The results demonstrate that functional connectivity can be an effective marker for the detection of changes in brain function in MCI subjects.

Aged↗

PubMed2005

Deforming the hippocampal map.

To investigate conjoint stimulus control over place cells, Fenton et al. (J Gen Physiol 116:191-209, 2000a) recorded while rats foraged in a cylinder with 45 degrees black and white cue cards on the wall. Card centers were 135 degrees apart. In probe trials, the cards were rotated together or apart by 25 degrees . Firing field centers shifted during these trials, stretching and shrinking the cognitive map. Fenton et al. (2000b) described this deformation with an ad hoc vector field equation. We consider what sorts of neural network mechanisms might be capable of accounting for their observations. In an abstract, maximum likelihood formulation, the rat's location is estimated by a conjoint probability density function of landmark positions. In an attractor neural network model, recurrent connections produce a bump of activity over a two-dimensional array of cells; the bump's position is influenced by landmark features such as distances or bearings. If features are chosen with appropriate care, the attractor network and maximum likelihood models yield similar results, in accord with previous demonstrations that recurrent neural networks can efficiently implement maximum likelihood computations (Pouget et al. Neural Comput 10:373-401, 1998; Deneve et al. Nat Neurosci 4:826-831, 2001).

Action Potentials↗

PubMed2003

Motor cortex hand area and speech: implications for the development of language.

Recently a growing body of evidence has suggested that a functional link exists between the hand motor area of the language dominant hemisphere and the regions subserving language processing. We examined the excitability of the hand motor area and the leg motor area during reading aloud and during non-verbal oral movements using transcranial magnetic stimulation (TMS). During reading aloud, but not before or afterwards, excitability was increased in the hand motor area of the dominant hemisphere. This reading effect was found to be independent of the duration of speech. No such effect could be found in the contralateral hemisphere. The excitability of the leg area of the motor cortex remained unchanged during reading aloud. The excitability during non-verbal oral movements was slightly increased in both hemispheres. Our results are consistent with previous findings and may indicate a specific functional connection between the hand motor area and the cortical language network.

Adult↗

PubMed1999

Dynamical features simulated by recurrent neural networks.

The evolution of two-dimensional neural network models with rank one connecting matrices and saturated linear transfer functions is dynamically equivalent to that of piecewise linear maps on an interval. It is shown that their iterative behavior ranges from being highly predictable, where almost every orbit accumulates to an attracting fixed point, to the existence of chaotic regions with cycles of arbitrarily large period.

Journal Article↗

PubMed1996

Dynamical computational properties of local cortical networks for visual and motor processing: a bayesian framework.

A major unsolved question concerns the interaction between the coding of information in the cortex and the collective neural operations (such as perceptual grouping, mental rotation) that can be performed on this information. A key property of the local networks in the cerebral cortex is to combine thalamocortical or feedforward information with horizontal cortico-cortical connections. Among different types of neural networks compatible with the known functional and architectural properties of the cortex, we show that there exist interesting bayesian solutions resulting in an optimal collective decision made by the neuronal population. We suggest that thalamo-cortical and cortico-cortical synaptic plasticity can be differentially modulated to optimize this collective bayesian decision process. We take two examples of cortical dynamics, one for perceptual grouping in MT, and the other one for mental rotation in M1. We show that a neural implementation of the bayesian principle is both computationally efficient to perform these tasks and consistent with the experimental data on the related neuronal activities. A major implication is that a similar collective decision mechanism should exist in different cortical regions due to the similarity of the cortical functional architecture.

Algorithms↗

PubMed2004

Steering molecular organization and host-guest interactions using two-dimensional nanoporous coordination systems.

Metal-organic coordination networks (MOCNs) have attracted wide interest because they provide a novel route towards porous materials that may find applications in molecular recognition, catalysis, gas storage and separation. The so-called rational design principle-synthesis of materials with predictable structures and properties-has been explored using appropriate organic molecular linkers connecting to metal nodes to control pore size and functionality of open coordination networks. Here we demonstrate the fabrication of surface-supported MOCNs comprising tailored pore sizes and chemical functionality by the modular assembly of polytopic organic carboxylate linker molecules and iron atoms on a Cu(100) surface under ultra-high-vacuum conditions. These arrays provide versatile templates for the handling and organization of functional species at the nanoscale, as is demonstrated by their use to accommodate C(60) guest molecules. Temperature-controlled studies reveal, at the single-molecule level, how pore size and chemical functionality determine the host-guest interactions.

Adsorption↗

PubMed2004

Response of complex networks to stimuli.

We consider the response of complex systems to stimuli and argue for the importance of both sensitivity, the possibility of large response to small stimuli, and robustness, the possibility of small response to large stimuli. Using a dynamic attractor network model for switching of patterns of behavior, we show that the scale-free topologies often found in nature enable more sensitive response to specific changes than do random networks. This property may be essential in networks where appropriate response to environmental change is critical and may, in such systems, be more important than features, such as connectivity, often used to characterize network topologies. Phenomenologically observed exponents for functional scale-free networks fall in a range corresponding to the onset of particularly high sensitivities, while still retaining robustness.

Biology↗

PubMed1996

Brown-Séquard and cerebral localization as illustrated by his ideas on aphasia.

Brown-Séquard's concept of localization was built on the phenomena of inhibition and dynamogenesis, constituting a dynamic system in which reflex mechanisms, that played a part not only in the spinal cord but in the brain as well, were considered of particular importance. The use of this concept is considered in Brown-Séquard's discussion of the subject of cerebral localization, and especially of aphasia. The origin and development of Brown-Séquard's ideas on aphasia from 1861 onwards are discussed, as is the part he possibly played in the transfer of knowledge from Paris to London (Broca and Jackson). In the 1870's Brown-Séquard debated on cerebral localization with Charcot before the Société de Biologie. Opposing the cluster theory of localization, Brown-Séquard developed the theory of "réseau de cellules anastomosées", a kind of network theory in which scattered cells subserving the same function are connected by nerve fibers. This was to him a plausible theory, with which he was able to explain the fact that damage in several locations may produce the same effect, and, to account for observations that some functions remain unimpaired despite extensive brain-injury. Although Brown-Séquard's arguments were not always valid, because they were based on imprecise observations, his dynamic model, nowadays, seems valuable. He influenced "anti-localizers" such as Goltz, but also Jackson and probably Von Monakow and Sherrington.

Aphasia↗

PubMed2003

Network information and connected correlations.

Entropy and information provide natural measures of correlation among elements in a network. We construct here the information theoretic analog of connected correlation functions: irreducible N-point correlation is measured by a decrease in entropy for the joint distribution of N variables relative to the maximum entropy allowed by all the observed N-1 variable distributions. We calculate the "connected information" terms for several examples and show that it also enables the decomposition of the information that is carried by a population of elements about an outside source.

Information Services↗

PubMed2006

Jacques Benoit Lecture. Information processing in the hypothalamus: peptides and analogue computation.

Peptides in the hypothalamus are not like conventional neurotransmitters; their release is not particularly associated with synapses, and their long half-lives mean that they can diffuse to distant targets. Peptides can act on their cells of origin to facilitate the development of patterned electrical activity, they can act on their neighbours to bind the collective activity of a neural population into a coherent signalling entity, and the co-ordinated population output can transmit waves of peptide secretion that act as a patterned hormonal analogue signal within the brain. At their distant targets, peptides can re-programme neural networks, by effects on gene expression, synaptogenesis, and by functionally rewiring connections by priming activity-dependent release.

Animals↗

PubMed1991

Network system: the integrated picture archiving and communication system with the hospital information system.

We describe the outline of Hokkaido University picture archiving and communication system (HU-PACS) and its network functions. HU-PACS processes 0.5 Gbytes of images daily through 10 acquisition devices. Functional integration of hospital information system (HIS) and PACS has been implemented. The HU-PACS can access common data base with HIS. Multi-image data-base systems provide fast throughput of image retrieval. The system is composed of 4 modules: (1) 2 image data-base systems (IDS), (2) 1 image management system (IMS), (3) image display terminals (IDT), and (4) 8 image acquisition nodes interfaced to 10 modalities and 1 film scanner. These 4 modules are connected by branch and loop type local area networks (LAN). HU-PACS has functions other than basic PACS functions. Images in optical disk library (ODL) are loaded onto magnetic disks (MD) in advance according to patient booking information, the images expected to be viewed are transferred to the local storage automatically, and the desired images can be pre-downloaded into local storage by instruction through HIS terminals.

Computer Communication Networks↗