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Search Results: 1 - 10 of 76 matches for " Mikail Rubinov "
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Weight-conserving characterization of complex functional brain networks
Mikail Rubinov,Olaf Sporns
Quantitative Biology , 2011, DOI: 10.1016/j.neuroimage.2011.03.069
Abstract: Complex functional brain networks are large networks of brain regions and functional brain connections. Statistical characterizations of these networks aim to quantify global and local properties of brain activity with a small number of network measures. Important functional network measures include measures of modularity (measures of the goodness with which a network is optimally partitioned into functional subgroups) and measures of centrality (measures of the functional influence of individual brain regions). Characterizations of functional networks are increasing in popularity, but are associated with several important methodological problems. These problems include the inability to characterize densely connected and weighted functional networks, the neglect of degenerate topologically distinct high-modularity partitions of these networks, and the absence of a network null model for testing hypotheses of association between observed nontrivial network properties and simple weighted connectivity properties. In this study we describe a set of methods to overcome these problems. Specifically, we generalize measures of modularity and centrality to fully connected and weighted complex networks, describe the detection of degenerate high-modularity partitions of these networks, and introduce a weighted-connectivity null model of these networks. We illustrate our methods by demonstrating degenerate high-modularity partitions and strong correlations between two complementary measures of centrality in resting-state functional magnetic resonance imaging (MRI) networks from the 1000 Functional Connectomes Project, an open-access repository of resting-state functional MRI datasets. Our methods may allow more sound and reliable characterizations and comparisons of functional brain networks across conditions and subjects.
Neurobiologically Realistic Determinants of Self-Organized Criticality in Networks of Spiking Neurons
Mikail Rubinov ,Olaf Sporns,Jean-Philippe Thivierge,Michael Breakspear
PLOS Computational Biology , 2011, DOI: 10.1371/journal.pcbi.1002038
Abstract: Self-organized criticality refers to the spontaneous emergence of self-similar dynamics in complex systems poised between order and randomness. The presence of self-organized critical dynamics in the brain is theoretically appealing and is supported by recent neurophysiological studies. Despite this, the neurobiological determinants of these dynamics have not been previously sought. Here, we systematically examined the influence of such determinants in hierarchically modular networks of leaky integrate-and-fire neurons with spike-timing-dependent synaptic plasticity and axonal conduction delays. We characterized emergent dynamics in our networks by distributions of active neuronal ensemble modules (neuronal avalanches) and rigorously assessed these distributions for power-law scaling. We found that spike-timing-dependent synaptic plasticity enabled a rapid phase transition from random subcritical dynamics to ordered supercritical dynamics. Importantly, modular connectivity and low wiring cost broadened this transition, and enabled a regime indicative of self-organized criticality. The regime only occurred when modular connectivity, low wiring cost and synaptic plasticity were simultaneously present, and the regime was most evident when between-module connection density scaled as a power-law. The regime was robust to variations in other neurobiologically relevant parameters and favored systems with low external drive and strong internal interactions. Increases in system size and connectivity facilitated internal interactions, permitting reductions in external drive and facilitating convergence of postsynaptic-response magnitude and synaptic-plasticity learning rate parameter values towards neurobiologically realistic levels. We hence infer a novel association between self-organized critical neuronal dynamics and several neurobiologically realistic features of structural connectivity. The central role of these features in our model may reflect their importance for neuronal information processing.
Symbiotic relationship between brain structure and dynamics
Mikail Rubinov, Olaf Sporns, Cees van Leeuwen, Michael Breakspear
BMC Neuroscience , 2009, DOI: 10.1186/1471-2202-10-55
Abstract: We show that coupled chaotic dynamics generate ordered and modular functional patterns, even on a random underlying structural connectivity. Consequently, structural connectivity becomes more modular as it rewires towards these functional patterns. Functional networks reflect the underlying structural networks on slow time scales, but significantly less so on faster time scales. In spite of ordered functional topology, structural networks remain robustly interconnected – and therefore small-world – due to the presence of central, inter-modular hub nodes. The noisy dynamics of these hubs enable them to persist despite ongoing rewiring and despite their comparative absence in functional networks.Our results outline a theoretical mechanism by which brain dynamics may facilitate neuroanatomical self-organization. We find time scale dependent differences between structural and functional networks. These differences are likely to arise from the distinct dynamics of central structural nodes.Modular small-world network topology may represent a basic organizational principle of neuroanatomical connectivity across multiple spatial scales [1-6]. Small-world networks are clustered (like ordered networks), and efficiently interconnected (like random networks) [1]. Modular networks are characterized by the presence of highly interconnected groups of nodes (modules) [7]. Hence a modular small-world connectivity reconciles the opposing demands of segregation and integration of functionally specialized brain areas [8] in the face of spatial wiring constraints [9]. However the mechanisms underlying the emergence of small-world connectivity in a developing nervous system remain unknown. In this study, we utilize nonlinear dynamical and network analyses to shed light on such mechanisms. We do this by using a model which examines the influence of neuronal dynamics on the underlying structural connectivity.Cortical structure and dynamics are highly interdependent. On relatively fast time
A Unifying Framework for Measuring Weighted Rich Clubs
Jeff Alstott,Pietro Panzarasa,Mikail Rubinov,Ed Bullmore,Petra Vertes
Computer Science , 2014, DOI: 10.1038/srep07258
Abstract: Network analysis can help uncover meaningful regularities in the organization of complex systems. Among these, rich clubs are a functionally important property of a variety of social, technological and biological networks. Rich clubs emerge when nodes that are somehow prominent or 'rich' (e.g., highly connected) interact preferentially with one another. The identification of rich clubs is non-trivial, especially in weighted networks, and to this end multiple distinct metrics have been proposed. Here we describe a unifying framework for detecting rich clubs which intuitively generalizes various metrics into a single integrated method. This generalization rests upon the explicit incorporation of randomized control networks into the measurement process. We apply this framework to real-life examples, and show that, depending on the selection of randomized controls, different kinds of rich-club structures can be detected, such as topological and weighted rich clubs.
Dynamic Change of Global and Local Information Processing in Propofol-Induced Loss and Recovery of Consciousness
Martin M. Monti ,Evan S. Lutkenhoff,Mikail Rubinov,Pierre Boveroux,Audrey Vanhaudenhuyse,Olivia Gosseries,Marie-Aurélie Bruno,Quentin Noirhomme,Mélanie Boly,Steven Laureys
PLOS Computational Biology , 2013, DOI: 10.1371/journal.pcbi.1003271
Abstract: Whether unique to humans or not, consciousness is a central aspect of our experience of the world. The neural fingerprint of this experience, however, remains one of the least understood aspects of the human brain. In this paper we employ graph-theoretic measures and support vector machine classification to assess, in 12 healthy volunteers, the dynamic reconfiguration of functional connectivity during wakefulness, propofol-induced sedation and loss of consciousness, and the recovery of wakefulness. Our main findings, based on resting-state fMRI, are three-fold. First, we find that propofol-induced anesthesia does not bear differently on long-range versus short-range connections. Second, our multi-stage design dissociated an initial phase of thalamo-cortical and cortico-cortical hyperconnectivity, present during sedation, from a phase of cortico-cortical hypoconnectivity, apparent during loss of consciousness. Finally, we show that while clustering is increased during loss of consciousness, as recently suggested, it also remains significantly elevated during wakefulness recovery. Conversely, the characteristic path length of brain networks (i.e., the average functional distance between any two regions of the brain) appears significantly increased only during loss of consciousness, marking a decrease of global information-processing efficiency uniquely associated with unconsciousness. These findings suggest that propofol-induced loss of consciousness is mainly tied to cortico-cortical and not thalamo-cortical mechanisms, and that decreased efficiency of information flow is the main feature differentiating the conscious from the unconscious brain.
An Uncontested Party Period of the Turkey Republic  [PDF]
Elnur Hasan Mikail, Anda? Karabulut
Open Journal of Political Science (OJPS) , 2016, DOI: 10.4236/ojps.2016.62023
Abstract: In an environment in which faction in the Turkish National Assembly increased and there occurred the need of political parties in politics, Mustafa Kemal announced a declaration to the press in 6 December 1922 that he would establish a political party named “People’s Party”. In 8 April 1923, Mustafa Kemal, in the capacity of the chairman of Anatolia and Rumelia Defense of Law Community, announced a declaration. This election declaration, at the same time, is in the form of a schedule preparation for the upcoming party. Later on, Mustafa Kemal and the congressmen in support of the establishment of the party started the preparations for the regulation.
The Political Developments in Turkey during Ataturk’s Period  [PDF]
Elnur Hasan Mikail, Anda? Karabulut
Open Journal of Political Science (OJPS) , 2017, DOI: 10.4236/ojps.2017.74040
Abstract: It has been understood that during the Seyh Sait Rebellion in East Anatolia, the Prime Minister Fethi Bey had a talk with the Leaders of this Party, that he had warned them and suggested to moderate or totally remove the Party organizations there. As this revolt became a dangerous face, the Government legalized the proposed Law concerning “the Religion must not be an instrument for the Politics” on the 25th of February 1925. However, after the questioning proposal in the C.H.P group with 18 signs concerning the facts in the East, there was held a vote of confidence for the Government and the cabinet resigned as a mistrust result for Fethi Bey with 60 dissential votes from 94 total votes. Ismet Pasa was charged with the duty to set up a new cabinet. In view of the Seyh Sait Rebellion, it has been seen that the Progressive-minded Party supported the cabinet of Fethi Bey and moreover, that the Leader Kazim Karabekir Pasa responded the martial Law decision of this Government as constructive and that he condemned this Rebellion by saying that: those who put the national presence in danger by procuring the religion as an instrument are deserving curse. This behaviour is infidelity to the country about the Rebellion.
Vladimir Putin Era Russian Foreign Policy  [PDF]
Elnur Hasan Mikail, Muhsin Yilmazchoban
Open Journal of Political Science (OJPS) , 2018, DOI: 10.4236/ojps.2018.84024
Abstract: The primary reason for the Putin’s increasing popularity is the broke out of the Second Chechen War. Russia has not got a homogenous structure; she embodies 100 nations together with 16 autonomous republics and 30 autonomous regions. Such an existing number and the South Caucasia where the most Muslims lived created problems for the Moscow government. In 1991 and 1992, a war broke out in North Ossetia and Ingushetia; there happened tensions in the Daghistan and Bashkir Republic autonomous regions. In the independence referendum held in March 1992 in Tatarstan, one of the largest regions with a one million population, 61% vote in favor was pulled. The most serious one among them is Chechnya of which Russia tried to prevent the seperatist movement. The Russian-Chechen history is entirely full of wars and large scale cruelties. Collaborating with Germans in 1944 Stalin banished almost all the population into the Kazakhstan steppes. Thousands of Chechens endeavoured to survive then.
On some topological properties of generalized difference sequence spaces
Mikail Et
International Journal of Mathematics and Mathematical Sciences , 2000, DOI: 10.1155/s0161171200002325
Abstract: We obtain some topological results of the sequence spaces Δm(X), where Δm(X)={x=(xk):(Δmxk)∈X},   (m∈ℕ), and X is any sequence space. We compute the pα-, pβ-, and pγ-duals of l∞,c, and c0 and we investigate the N-(or null) dual of the sequence spaces Δm(l∞),   Δm(c), and Δm(c0). Also we show that any matrix map from Δm(l∞) into a BK-space which does not contain any subspace isomorphic to Δm(l∞) is compact.
In vitro trypanocidal effect of methanolic extract of Sclerocarya birrea, Commiphora kerstingii and Khaya senegalensis
HG Mikail
African Journal of Biotechnology , 2009,
Abstract: The anti-trypanosomal activity of methanolic extract of Sclerocarya birrea, Commiphora kerstingii and Khaya senegalensis were evaluated against Trypanosoma brucei brucei in vitro at concentrations of 2 and 4 mg/ml. Susceptibility of the organism was determined in culture medium containing 5% dextrose and 0.9% saline solution alone as control and 2 and 4 mg/ml of these plants extracts in the same solution. Complete mortality of the organism was observed at almost all the concentrations within 30 min; the organism however survived for almost 3 h in the control test tube. The result suggests that S. birrea, C. kerstingii and K. sengalensis extracts may possess some trypanocidal principles which may require further elucidation.
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