Network Level (network + level)

Distribution by Scientific Domains

Selected Abstracts

Relationship between GABAergic interneurons migration and early neocortical network activity

Ana D. de Lima
Abstract Available evidence converges to suggest that during the early development of the cerebral cortex, the emergence of the spontaneous network activity chronologically overlap with the end of the cell migration period in the developing cortex. We approached the functional regulation of neuronal migration in a culture model of neocortical networks, using time lapses to detect migratory movements, calcium-imaging to assess the activity of migratory neurons, and immunocytochemical methods to identify the migratory cells retrospectively. In cell cultures, early physiological development and cell migration are reproduced at a local network level, thus allowing the study of the interrelationships between cell migration and network development independent of the topographical complexity. Neurons migrate at least until 12 days in vitro and GABAergic neurons migrate faster compared with non-GABAergic neurons. A decline of migratory activity was coincident with the development of spontaneous synchronous network activity. Migrating interneurons did not participate in synchronous network activity, but interneurons that ended cell migration during observation time frequently engaged in synchronous activity within less than an hour. Application of GABAA and ionotropic glutamate receptor antagonists significantly increased the number of migrating GABAergic neurons without changing the dynamics of the migratory movements. Thus, neurotransmitters released by early network activity might favor the termination of neuronal migration. These results reinforce the idea that network activity plays an important role in the development of late-born GABAergic cells. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2009 [source]

Attention , oscillations and neuropharmacology

Gustavo Deco
Abstract Attention is a rich psychological and neurobiological construct that influences almost all aspects of cognitive behaviour. It enables enhanced processing of behaviourally relevant stimuli at the expense of irrelevant stimuli. At the cellular level, rhythmic synchronization at local and long-range spatial scales complements the attention-induced firing rate changes of neurons. The former is hypothesized to enable efficient communication between neuronal ensembles tuned to spatial and featural aspects of the attended stimulus. Recent modelling studies suggest that the rhythmic synchronization in the gamma range may be mediated by a fine balance between N -methyl- d -aspartate and ,-amino-3-hydroxy-5-methylisoxazole-4-propionate postsynaptic currents, whereas other studies have highlighted the possible contribution of the neuromodulator acetylcholine. This review summarizes some recent modelling and experimental studies investigating mechanisms of attention in sensory areas and discusses possibilities of how glutamatergic and cholinergic systems could contribute to increased processing abilities at the cellular and network level during states of top-down attention. [source]

Loss of zolpidem efficacy in the hippocampus of mice with the GABAA receptor ,2 F77I point mutation

D. W. Cope
Abstract Zolpidem is a hypnotic benzodiazepine site agonist with some ,-aminobutyric acid (GABA)A receptor subtype selectivity. Here, we have tested the effects of zolpidem on the hippocampus of ,2 subunit (,2F77I) point mutant mice. Analysis of forebrain GABAA receptor expression with immunocytochemistry, quantitative [3H]muscimol and [35S] t-butylbicyclophosphorothionate (TBPS) autoradiography, membrane binding with [3H]flunitrazepam and [3H]muscimol, and comparison of miniature inhibitory postsynaptic current (mIPSC) parameters did not reveal any differences between homozygous ,2I77/I77 and ,2F77/F77 mice. However, quantitative immunoblot analysis of ,2I77/I77 hippocampi showed some increased levels of ,2, ,1, ,4 and , subunits, suggesting that differences between strains may exist in unassembled subunit levels, but not in assembled receptors. Zolpidem (1 µm) enhanced the decay of mIPSCs in CA1 pyramidal cells of control (C57BL/6J, ,2F77/F77) mice by ,,60%, and peak amplitude by ,,20% at 33,34 °C in vitro. The actions of zolpidem (100 nm or 1 µm) were substantially reduced in ,2I77/I77 mice, although residual effects included a 9% increase in decay and 5% decrease in peak amplitude. Similar results were observed in CA1 stratum oriens/alveus interneurons. At network level, the effect of zolpidem (10 µm) on carbachol-induced oscillations in the CA3 area of ,2I77/I77 mice was significantly different compared with controls. Thus, the ,2F77I point mutation virtually abolished the actions of zolpidem on GABAA receptors in the hippocampus. However, some residual effects of zolpidem may involve receptors that do not contain the ,2 subunit. [source]

Detecting functional nodes in large-scale cortical networks with functional magnetic resonance imaging: A principal component analysis of the human visual system

Christine Ecker
Abstract This study aimed to demonstrate how a regional variant of principal component analysis (PCA) can be used to delineate the known functional subdivisions of the human visual system. Unlike conventional eigenimage analysis, PCA was carried out as a second-level analysis subsequent to model-based General Linear Model (GLM)-type functional activation mapping. Functional homogeneity of the functional magnetic resonance imaging (fMRI) time series within and between clusters was examined on several levels of the visual network, starting from the level of individual clusters up to the network level comprising two or more distinct visual regions. On each level, the number of significant components was identified and compared with the number of clusters in the data set. Eigenimages were used to examine the regional distribution of the extracted components. It was shown that voxels within individual clusters and voxels located in bilateral homologue visual regions can be represented by a single component, constituting the characteristic functional specialization of the cluster(s). If, however, PCA was applied to time series of voxels located in functionally distinct visual regions, more than one component was observed with each component being dominated by voxels in one of the investigated regions. The model of functional connections derived by PCA was in accordance with the well-known functional anatomy and anatomical connectivity of the visual system. PCA in combination with conventional activation mapping might therefore be used to identify the number of functionally distinct nodes in an fMRI data set in order to generate a model of functional connectivity within a neuroanatomical network. Hum Brain Mapp, 2006. © 2006 Wiley-Liss, Inc. [source]

Soft real-time communications over Bluetooth under interferences from ISM devices

J. L. Sevillano
Abstract Bluetooth is a suitable technology to support soft real-time applications like multimedia streams at the personal area network level. In this paper, we analytically evaluate the worst-case deadline failure probability of Bluetooth packets under co-channel interference as a way to provide statistical guarantees when transmitting soft real-time traffic using ACL links. We consider the interference from independent Bluetooth devices, as well as from other devices operating in the ISM band like 802.11b/g and Zigbee. Finally, we show as an example how to use our model to obtain some results for the transmission of a voice stream. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Adenosine A2A receptors, dopamine D2 receptors and their interactions in Parkinson's disease

Kjell Fuxe MD
Abstract Future therapies in Parkinson's disease may substantially build on the existence of intra-membrane receptor,receptor interactions in DA receptor containing heteromeric receptor complexes. The A2A/D2 heteromer is of substantial interest in view of its specific location in cortico-striatal glutamate terminals and in striato-pallidal GABA neurons. Antagonistic A2A/D2 receptor interactions in this heteromer demonstrated at the cellular level, and at the level of the striato-pallidal GABA neuron and at the network level made it possible to suggest A2A antagonists as anti-parkinsonian drugs. The major mechanism is an enhancement of D2 signaling leading to attenuation of hypokinesia, tremor, and rigidity in models of Parkinson's disease with inspiring results in two clinical trials. Other interactions are antagonism at the level of the adenylyl cyclase; heterologous sensitization at the A2A activated adenylyl cyclase by persistent D2 activation and a compensatory up-regulation of A2A receptors in response to intermittent Levodopa treatment. An increased dominance of A2A homomers over D2 homomers and A2A/D2 heteromers after intermittent Levodopa treatment may therefore contribute to development of Levodopa induced dyskinesias and to the wearing off of the therapeutic actions of Levodopa giving additional therapeutic roles of A2A antagonists. Their neuroprotective actions may involve an increase in the retrograde trophic signaling in the nigro-striatal DA system. © 2007 Movement Disorder Society [source]

Bauwerks-Management-System (BMS) , Werkzeug zur Substanzerhaltung für Verkehrsbauwerke

BAUTECHNIK, Issue 10 2004
Peter Haardt Dr.-Ing.
Das Bundesfernstraßennetz beinhaltet eine große Anzahl von Brücken und anderen Ingenieurbauwerken, wie Tunnel, Lärmschutzeinrichtungen und Stützwände. Die für diese Bauwerke aufzustellenden Erhaltungsprogramme erfordern nicht nur erhebliche Geldmittel, sondern beeinflussen auch Wirtschaft und Gesellschaft insgesamt. Neben den ständig wachsenden Verkehrsbeanspruchungen zwingen die ungünstiger werdende Altersstruktur und der wirtschaftliche Einsatz der zur Verfügung stehenden Haushaltsmittel alle Beteiligten dazu, die Erhaltung der Bundesfernstraßen zu systematisieren, um auch zukünftig den Verkehrsteilnehmern eine ausreichende Qualität der Verkehrswege zu sichern. Diese Aufgabe wird durch die Anwendung eines umfassenden Management Systems (Bauwerks-Management-System, BMS) unterstützt und erleichtert. Das BMVBW realisiert ein umfassendes Bauwerks-Management-System mit Teil modulen für Bundes- und Länderverwaltungen, welches als Hilfsmittel für die Erstellung von Erhaltungsplanungen dient und als Controlling-Instrument die Realisierung von Zielen und Strategien ermöglicht. Angestrebt werden damit eine bundesweite Vereinheitlichung von Planungsverfahren sowie die Verbesserung der Wirtschaftlichkeit im Rahmen der Erhaltung der Bauwerke des Bundesfernstraßennetzes. Der Beitrag beschreibt neben den bereits existierenden Regelungen und Verfahren die aktuellen Entwicklungen von Verfahren zur Unterstützung der Erhaltungsplanungen, die derzeit für Computeranwendungen bereitgestellt werden. Wesentliche Einzelthemen sind Informationsbereitstellung, Entwicklung von Erhaltungsstrategien und Bewertungsverfahren auf Objekt- und Netzebene. Bridge Management System (BMS) , a tool for maintenance of highway structures. The federal road network of Germany contains a large number of highway structures like bridges, tunnels, retaining walls and others. The maintenance programs to be prepared for this purpose not only require a high budget, but also influence the economy and society as a whole. Due to growing volumes of traffic and higher weights of trucks, bridges are subjected to increasing loads which implies that maintenance costs will be rising in the future. Considering the fact that financial resources become continuously tighter, the maintenance costs have to be spent in a way to obtain the greatest possible benefits. This task will in the future be supported by the application of individual computer programs in the frame of a comprehensive Management System (Bridge Management System, BMS). Firstly, the BMS is to provide the Federal Ministry with an overview of the current situation at the overall network level, and allow it to come to financial requirements as well as strategies for realising long-term objectives. Secondly, the states and authorities are to be supplied with recommendations for performing improvements at the object level and the state network level in compliance with given strategies and budgetary restrictions. The paper describes the existing regulations as well as procedures for the support of maintenance planning which are currently being developed for computer application. Important topics are information technology, development of maintenance strategies and assessment procedures on object and network level. [source]

Maintaining video quality and optimizing video delivery over the bandwidth constrained DSL last mile through intelligent packet drop

Tom N. M. Van Caenegem
The technological challenges for an Internet Protocol television (IPTV) service provider to bring high quality video services into the home through a dedicated bandwidth limited digital subscriber line (DSL) access link are significant. However, at the same time, the dedicated DSL link provides certain opportunities as it allows for service customization on the network level, without impacting any other customers. In this paper, the concept of intelligent packet drop inside a digital subscriber line access multiplexer (DSLAM) is introduced. Intelligent packet drop makes use of the fact that some packets containing video information (e.g., I-picture or P-picture) are more important than others (e.g., B-picture), and this importance level can be indicated in the packet header. When congestion in the DSLAM occurs, the low priority packets are preferentially dropped. Provided some (simple) picture loss concealment is performed in the set-top box, intelligent packet drop will not significantly impact the quality of experience (QoE), as evidenced by subjective tests that have been conducted. Simulations have shown that the intelligent packet drop in a DSLAM enables the IPTV service provider to increase the number of customers eligible for a given IPTV service package delivered over the DSL link. It also enables fast channel change (FCC) service without dedicated bandwidth overhead. © 2008 Alcatel-Lucent. [source]