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Regulation of irregular neuronal firing by autaptic transmission
Daqing Guo, Shengdun Wu, Mingming Chen, Matjaž Perc, Yangsong Zhang, Jingling Ma, Yan Cui, Peng Xu, Yang Xia, Dezhong Yao, 2016, izvirni znanstveni članek

Opis: The importance of self-feedback autaptic transmission in modulating spike-time irregularity is still poorly understood. By using a biophysical model that incorporates autaptic coupling, we here show that self-innervation of neurons participates in the modulation of irregular neuronal firing, primarily by regulating the occurrence frequency of burst firing. In particular, we find that both excitatory and electrical autapses increase the occurrence of burst firing, thus reducing neuronal firing regularity. In contrast, inhibitory autapses suppress burst firing and therefore tend to improve the regularity of neuronal firing. Importantly, we show that these findings are independent of the firing properties of individual neurons, and as such can be observed for neurons operating in different modes. Our results provide an insightful mechanistic understanding of how different types of autapses shape irregular firing at the single-neuron level, and they highlight the functional importance of autaptic self-innervation in taming and modulating neurodynamics.
Ključne besede: neuronal dynamics, autapse, regulation, excitation
Objavljeno: 23.06.2017; Ogledov: 75; Prenosov: 0
.pdf Polno besedilo (2,65 MB)

Progressive glucose stimulation of islet beta cells reveals a transition from segregated to integrated modular functional connectivity patterns
Marjan Rupnik, Andraž Stožer, Marko Gosak, Rene Markovič, Marko Marhl, Jurij Dolenšek, 2015, izvirni znanstveni članek

Opis: Collective beta cell activity in islets of Langerhans is critical for the supply of insulin within an organism. Even though individual beta cells are intrinsically heterogeneous, the presence of intercellular coupling mechanisms ensures coordinated activity and a well-regulated exocytosis of insulin. In order to get a detailed insight into the functional organization of the syncytium, we applied advanced analytical tools from the realm of complex network theory to uncover the functional connectivity pattern among cells composing the intact islet. The procedure is based on the determination of correlations between long temporal traces obtained from confocal functional multicellular calcium imaging of beta cells stimulated in a stepwise manner with a range of physiological glucose concentrations. Our results revealed that the extracted connectivity networks are sparse for low glucose concentrations, whereas for higher stimulatory levels they become more densely connected. Most importantly, for all ranges of glucose concentration beta cells within the islets form locally clustered functional sub-compartments, thereby indicating that their collective activity profiles exhibit a modular nature. Moreover, we show that the observed non-linear functional relationship between different network metrics and glucose concentration represents a well-balanced setup that parallels physiological insulin release.
Ključne besede: endocrinology, computational biophysics, calcium signalling, biological physics
Objavljeno: 23.06.2017; Ogledov: 80; Prenosov: 0
.pdf Polno besedilo (957,14 KB)

Optimal interdependence between networks for the evolution of cooperation
Zhen Wang, Attila Szolnoki, Matjaž Perc, 2013, izvirni znanstveni članek

Opis: Recent research has identified interactions between networks as crucial for the outcome of evolutionary games taking place on them. While the consensus is that interdependence does promote cooperation by means of organizational complexity and enhanced reciprocity that is out of reach on isolated networks, we here address the question just how much interdependence there should be. Intuitively, one might assume the more the better. However, we show that in fact only an intermediate density of sufficiently strong interactions between networks warrants an optimal resolution of social dilemmas. This is due to an intricate interplay between the heterogeneity that causes an asymmetric strategy flow because of the additional links between the networks, and the independent formation of cooperative patterns on each individual network. Presented results are robust to variations of the strategy updating rule, the topology of interdependent networks, and the governing social dilemma, thus suggesting a high degree of universality.
Ključne besede: social dilemma, cooperation, public goods, biased utility, interdependent networks, statistical physics of social systems
Objavljeno: 23.06.2017; Ogledov: 35; Prenosov: 0
.pdf Polno besedilo (658,72 KB)

Maximal neighbor similarity reveals real communities in networks
Krista Rizman Žalik, 2015, izvirni znanstveni članek

Opis: An important problem in the analysis of network data is the detection of groups of densely interconnected nodes also called modules or communities. Community structure reveals functions and organizations of networks. Currently used algorithms for community detection in large-scale realworld networks are computationally expensive or require a priori information such as the number or sizes of communities or are not able to give the same resulting partition in multiple runs. In this paper we investigate a simple and fast algorithm that uses the network structure alone and requires neither optimization of pre-defined objective function nor information about number of communities. We propose a bottom up community detection algorithm in which starting from communities consisting of adjacent pairs of nodes and their maximal similar neighbors we find real communities. We show that the overall advantage of the proposed algorithm compared to the other community detection algorithms is its simple nature, low computational cost and its very high accuracy in detection communities of different sizes also in networks with blurred modularity structure consisting of poorly separated communities. All communities identified by the proposed method for facebook network and E-Coli transcriptional regulatory network have strong structural and functional coherence.
Ključne besede: networks, real communities, neighbor similarity
Objavljeno: 23.06.2017; Ogledov: 52; Prenosov: 0
.pdf Polno besedilo (2,21 MB)

Leaders should not be conformists in evolutionary social dilemmas
Attila Szolnoki, Matjaž Perc, 2016, izvirni znanstveni članek

Opis: The most common assumption in evolutionary game theory is that players should adopt a strategy that warrants the highest payoff. However, recent studies indicate that the spatial selection for cooperation is enhanced if an appropriate fraction of the population chooses the most common rather than the most profitable strategy within the interaction range. Such conformity might be due to herding instincts or crowd behavior in humans and social animals. In a heterogeneous population where individuals differ in their degree, collective influence, or other traits, an unanswered question remains who should conform. Selecting conformists randomly is the simplest choice, but it is neither a realistic nor the optimal one. We show that, regardless of the source of heterogeneity and game parametrization, socially the most favorable outcomes emerge if the masses conform. On the other hand, forcing leaders to conform significantly hinders the constructive interplay between heterogeneity and coordination, leading to evolutionary outcomes that are worse still than if conformists were chosen randomly. We conclude that leaders must be able to create a following for network reciprocity to be optimally augmented by conformity. In the opposite case, when leaders are castrated and made to follow, the failure of coordination impairs the evolution of cooperation.
Ključne besede: cooperation, public goods, selection, physics of social systems
Objavljeno: 23.06.2017; Ogledov: 29; Prenosov: 1
.pdf Polno besedilo (620,37 KB)

Languages cool as they expand: allometric scaling and the decreasing need for new words
Alexander Petersen, Joel Tenenbaum, Shlomo Havlin, Harry Eugene Stanley, Matjaž Perc, 2012, izvirni znanstveni članek

Opis: We analyze the occurrence frequencies of over 15 million words recorded in millions of books published during the past two centuries in seven different languages. For all languages and chronological subsets of the data we confirm that two scaling regimes characterize the word frequency distributions, with only the more common words obeying the classic Zipf law. Using corpora of unprecedented size, we test the allometric scaling relation between the corpus size and the vocabulary size of growing languages to demonstrate a decreasing marginal need for new words, a feature that is likely related to the underlying correlations between words. We calculate the annual growth fluctuations of word use which has a decreasing trend as the corpus size increases, indicating a slowdown in linguistic evolution following language expansion. This cooling pattern forms the basis of a third statistical regularity, which unlike the Zipf and the Heaps law, is dynamical in nature.
Ključne besede: culturomics, society, culture, quantitative linguistics, physics of social systems
Objavljeno: 23.06.2017; Ogledov: 41; Prenosov: 0
.pdf Polno besedilo (2,03 MB)

Interdependent network reciprocity in evolutionary games
Zhen Wang, Attila Szolnoki, Matjaž Perc, 2013, izvirni znanstveni članek

Opis: Besides the structure of interactions within networks, also the interactions between networks are of the outmost importance. We therefore study the outcome of the public goods game on two interdependent networks that are connected by means of a utility function, which determines how payoffs on both networks jointly influence the success of players in each individual network. We show that an unbiased coupling allows the spontaneous emergence of interdependent network reciprocity, which is capable to maintain healthy levels of public cooperation even in extremely adverse conditions. The mechanism, however, requires simultaneous formation of correlated cooperator clusters on both networks. If this does not emerge or if the coordination process is disturbed, network reciprocity fails, resulting in the total collapse of cooperation. Network interdependence can thus be exploited effectively to promote cooperation past the limits imposed by isolated networks, but only if the coordination between the interdependent networks is not disturbed.
Ključne besede: social dilemma, cooperation, public goods, biased utility, interdependent networks, statistical physics of social systems
Objavljeno: 23.06.2017; Ogledov: 31; Prenosov: 0
.pdf Polno besedilo (741,04 KB)

If players are sparse social dilemmas are too: importance of percolation for evolution of cooperation
Zhen Wang, Attila Szolnoki, Matjaž Perc, 2012, izvirni znanstveni članek

Opis: Spatial reciprocity is a well known tour de force of cooperation promotion. A thorough understanding of the effects of different population densities is therefore crucial. Here we study the evolution of cooperation in social dilemmas on different interaction graphs with a certain fraction of vacant nodes. We find that sparsity may favor the resolution of social dilemmas, especially if the population density is close to the percolation threshold of the underlying graph. Regardless of the type of the governing social dilemma as well as particularities of the interaction graph, we show that under pairwise imitation the percolation threshold is a universal indicator of how dense the occupancy ought to be for cooperation to be optimally promoted. We also demonstrate that myopic updating, due to the lack of efficient spread of information via imitation, renders the reported mechanism dysfunctional, which in turn further strengthens its foundations.
Ključne besede: cooperation, public goods, punishment, phase transitions, physics of social systems
Objavljeno: 23.06.2017; Ogledov: 52; Prenosov: 0
.pdf Polno besedilo (413,53 KB)

Homophily in coauthorship networks of East European sociologists
Marian-Gabriel Hâncean, Matjaž Perc, 2016, izvirni znanstveni članek

Opis: We study to what degree and how homophily and network properties affect individual citation counts of researchers in the sociology departments of three East European countries, namely Poland, Romania, and Slovenia. We built first-order personal coauthorship networks out of the Web of Science publication records. Each sociologist is assigned as a focal node or ego, while her coauthors are alters. We analyze the data using structural measurements methods, hierarchical regression models, and we make visualizations based on the clustered graph technique. For all three populations, our results indicate that the mean score of the citations of alters substantially predicts the citation counts of egos. In particular, citation similarity increases the chances for coauthorship ties. Evidence for the impact of network properties on the citation levels of egos is mixed. For Poland, normalized ego-betweenness shows a negative effect on citation counts, while network density displays a positive one. For Romania and Slovenia, network characteristics have only a minor impact. Even if the visual summarization of the personal networks uncovers a wide palette of coauthorship patterns, homophily appears to be pervasive. These results are relevant for domestic policy makers who aim to improve the aggregated research performance in East European countries.
Ključne besede: social network, sociology, homophily, physics of social systems
Objavljeno: 23.06.2017; Ogledov: 18; Prenosov: 0
.pdf Polno besedilo (1,21 MB)

Excessive abundance of common resources deters social responsibility
Xiaojie Chen, Matjaž Perc, 2014, izvirni znanstveni članek

Opis: We study the evolution of cooperation in the collective-risk social dilemma game, where the risk is determined by a collective target that must be reached with individual contributions. All players initially receive endowments from the available amount of common resources. While cooperators contribute part of their endowment to the collective target, defectors do not. If the target is not reached, the endowments of all players are lost. In our model, we introduce a feedback between the amount of common resources and the contributions of cooperators. We show that cooperation can be sustained only if the common resources are preserved but never excessively abound. This, however, requires a delicate balance between the amount of common resources that initially exist, and the amount cooperators contribute to the collective target. Exceeding critical thresholds in either of the two amounts leads to loss of cooperation, and consequently to the depletion of common resources.
Ključne besede: social dilemma, evolutionary games, public goods, abundance, phase transitions, physics of social systems
Objavljeno: 23.06.2017; Ogledov: 45; Prenosov: 1
.pdf Polno besedilo (950,12 KB)

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