1. Disinhibition-induced transitions between absence and tonic-clonic epileptic seizuresMatjaž Perc, Qingyun Wang, Denggui Fan, 2015, izvirni znanstveni članek Opis: Electrophysiological experiments have long revealed the existence of two-way transitions between absence and tonic-clonic epileptic seizures in the cerebral cortex. Based on a modified spatially-extended Taylor & Baier neural field model, we here propose a computational framework to mathematically describe the transition dynamics between these epileptic seizures. We first demonstrate the existence of various transition types that are induced by disinhibitory functions between two inhibitory variables in an isolated Taylor & Baier model. Moreover, we show that these disinhibition-induced transitions can lead to stable tonic-clonic oscillations as well as periodic spike with slow-wave discharges, which are the hallmark of absence seizures. We also observe fascinating dynamical states, such as periodic 2-spike with slow-wave discharges, tonic death, bursting oscillations, as well as saturated firing. Most importantly, we identify paths that represent physiologically plausible transitions between absence and tonic-clonic seizures in the modified spatially-extended Taylor & Baier model. Ključne besede: epilepsy, neuronal dynamics, synchronization, biophysics Objavljeno: 23.06.2017; Ogledov: 126; Prenosov: 25 Celotno besedilo (2,30 MB) |
2. Synchronous bursts on scale-free neuronal networks with attractive and repulsive couplingQingyun Wang, Guanrong Chen, Matjaž Perc, 2011, izvirni znanstveni članek Opis: This paper investigates the dependence of synchronization transitions of bursting oscillations on the information transmission delay over scale-free neuronal networks with attractive and repulsive coupling. It is shown that for both types of coupling, the delay always plays a subtle role in either promoting or impairing synchronization. In particular, depending on the inherent oscillation period of individual neurons, regions of irregular and regular propagating excitatory fronts appear intermittently as the delay increases. These delay-induced synchronization transitions are manifested as well-expressed minima in the measure for spatiotemporal synchrony. For attractive coupling, the minima appear at every integer multiple of the average oscillation period, while for the repulsive coupling, they appear at every odd multiple of the half of the average oscillation period. The obtained results are robust to the variations of the dynamics of individual neurons, the system size, and the neuronal firing type. Hence, they can be used to characterize attractively or repulsively coupled scale-free neuronal networks with delays. Ključne besede: synchronization, neuronal networks, noise, stochastic processes, scale-free networks, information transmission delay Objavljeno: 19.06.2017; Ogledov: 202; Prenosov: 18 Celotno besedilo (933,65 KB) |
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4. Comprehensible predictive modeling using regularized logistic regression and comorbidity based featuresGregor Štiglic, Nino Fijačko, Petra Povalej, Fei Wang, Alexandros Kalousis, Boris Delibašić, Zoran Obradović, 2015, izvirni znanstveni članek Opis: Different studies have demonstrated the importance of comorbidities to better understand the origin and evolution of medical complications. This study focuses on improvement of the predictive model interpretability based on simple logical features representing comorbidities. We use group lasso based feature interaction discovery followed by a post-processing step, where simple logic terms are added. In the final step, we reduce the feature set by applying lasso logistic regression to obtain a compact set of non-zero coefficients that represent a more comprehensible predictive model. The effectiveness of the proposed approach was demonstrated on a pediatric hospital discharge dataset that was used to build a readmission risk estimation model. The evaluation of the proposed method demonstrates a reduction of the initial set of features in a regression model by 72%, with a slight improvement in the Area Under the ROC Curve metric from 0.763 (95% CI: 0.755%0.771) to 0.769 (95% CI: 0.761%0.777). Additionally, our results show improvement in comprehensibility of the final predictive model using simple comorbidity based terms for logistic regression. Ključne besede: predictive models, logistic regression, readmission classification, comorbidities Objavljeno: 19.06.2017; Ogledov: 170; Prenosov: 36 Celotno besedilo (1,13 MB) |
5. If players are sparse social dilemmas are too: importance of percolation for evolution of cooperationZhen 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: 146; Prenosov: 14 Celotno besedilo (413,53 KB) |
6. Interdependent network reciprocity in evolutionary gamesZhen 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: 124; Prenosov: 21 Celotno besedilo (741,04 KB) |
7. Optimal interdependence between networks for the evolution of cooperationZhen 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: 138; Prenosov: 21 Celotno besedilo (658,72 KB) |
8. Wisdom of groups promotes cooperation in evolutionary social dilemmasAttila Szolnoki, Zhen Wang, Matjaž Perc, 2012, izvirni znanstveni članek Opis: Whether or not to change strategy depends not only on the personal success of each individual, but also on the success of others. Using this as motivation, we study the evolution of cooperation in games that describe social dilemmas, where the propensity to adopt a different strategy depends both on individual fitness as well as on the strategies of neighbors. Regardless of whether the evolutionary process is governed by pairwise or group interactions, we show that plugging into the wisdom of groups strongly promotes cooperative behavior. The more the wider knowledge is taken into account the more the evolution of defectors is impaired. We explain this by revealing a dynamically decelerated invasion process, by means of which interfaces separating different domains remain smooth and defectors therefore become unable to efficiently invade cooperators. This in turn invigorates spatial reciprocity and establishes decentralized decision making as very beneficial for resolving social dilemmas. Ključne besede: cooperation, public goods, wisdom of crowds, phase transitions, physics of social systems Objavljeno: 23.06.2017; Ogledov: 248; Prenosov: 24 Celotno besedilo (646,99 KB) |
9. Self-organization towards optimally interdependent networks by means of coevolutionZhen Wang, Attila Szolnoki, Matjaž Perc, 2014, izvirni znanstveni članek Opis: Coevolution between strategy and network structure is established as a means to arrive at the optimal conditions needed to resolve social dilemmas. Yet recent research has highlighted that the interdependence between networks may be just as important as the structure of an individual network. We therefore introduce the coevolution of strategy and network interdependence to see whether this can give rise to elevated levels of cooperation in the prisonerʼs dilemma game. We show that the interdependence between networks self-organizes so as to yield optimal conditions for the evolution of cooperation. Even under extremely adverse conditions, cooperators can prevail where on isolated networks they would perish. This is due to the spontaneous emergence of a two-class society, with only the upper class being allowed to control and take advantage of the interdependence. Spatial patterns reveal that cooperators, once arriving at the upper class, are much more competent than defectors in sustaining compact clusters of followers. Indeed, the asymmetric exploitation of interdependence confers to them a strong evolutionary advantage that may resolve even the toughest of social dilemmas. Ključne besede: coevolution, cooperation, interdependent networks, evolutionary games, collective phenomena, self-organization, phase transitions, physics of social systems Objavljeno: 03.07.2017; Ogledov: 141; Prenosov: 36 Celotno besedilo (887,51 KB) |
10. Adaptive and bounded investment returns promote cooperation in spatial public goods gamesXiaojie Chen, Yongkui Liu, Yonghui Zhou, Long Wang, Matjaž Perc, 2012, izvirni znanstveni članek Opis: The public goods game is one of the most famous models for studying the evolution of cooperation in sizable groups. The multiplication factor in this game can characterize the investment return from the public good, which may be variable depending on the interactive environment in realistic situations. Instead of using the same universal value, here we consider that the multiplication factor in each group is updated based on the differences between the local and global interactive environments in the spatial public goods game, but meanwhile limited to within a certain range. We find that the adaptive and bounded investment returns can significantly promote cooperation. In particular, full cooperation can be achieved for high feedback strength when appropriate limitation is set for the investment return. Also, we show that the fraction of cooperators in the whole population can become larger if the lower and upper limits of the multiplication factor are increased. Furthermore, in comparison to the traditionally spatial public goods game where the multiplication factor in each group is identical and fixed, we find that cooperation can be better promoted if the multiplication factor is constrained to adjust between one and the group size in our model. Our results highlight the importance of the locally adaptive and bounded investment returns for the emergence and dominance of cooperative behavior in structured populations. Ključne besede: cooperation, public goods, social dilemmas, physics of social systems Objavljeno: 19.06.2017; Ogledov: 120; Prenosov: 23 Celotno besedilo (590,51 KB) |