Cooperation transitions in social games induced by aspiration-driven players.

Cooperation and defection are social traits whose evolutionary origin is still unresolved. Recent behavioral experiments with humans suggested that strategy changes are driven mainly by the individuals' expectations and not by imitation. This work theoretically analyzes and numerically explores an aspiration-driven strategy updating in a well-mixed population playing games. The payoffs of the game matrix and the aspiration are condensed into just two parameters that allow a comprehensive description of the dynamics. We find continuous and abrupt transitions in the cooperation density with excellent agreement between theory and the Gillespie simulations. Under strong selection, the system can display several levels of steady cooperation or get trapped into absorbing states. These states are still relevant for experiments even when irrational choices are made due to their prolonged relaxation times. Finally, we show that for the particular case of the prisoner dilemma, where defection is the dominant strategy under imitation mechanisms, the self-evaluation update instead favors cooperation nonlinearly with the level of aspiration. Thus, our work provides insights into the distinct role between imitation and self-evaluation with no learning dynamics.

Generalized synchronization mediated by a flat coupling between structurally nonequivalent chaotic systems.

Synchronization of chaotic systems is usually investigated for structurally equivalent systems typically coupled through linear diffusive functions. Here, we focus on a particular type of coupling borrowed from a nonlinear control theory and based on the optimal placement of a sensor-a device measuring the chosen variable-and an actuator-a device applying the actuating (control) signal to a variable's derivative-in the response system, leading to the so-called flat control law. We aim to investigate the dynamics produced by a response system that is flat coupled to a drive system and to determine the degree of generalized synchronization between them using statistical and topological arguments. The general use of a flat control law for getting generalized synchronization is discussed.

Unveiling the Connectivity of Complex Networks Using Ordinal Transition Methods.

Ordinal measures provide a valuable collection of tools for analyzing correlated data series. However, using these methods to understand information interchange in the networks of dynamical systems, and uncover the interplay between dynamics and structure during the synchronization process, remains relatively unexplored. Here, we compare the ordinal permutation entropy, a standard complexity measure in the literature, and the permutation entropy of the ordinal transition probability matrix that describes the transitions between the ordinal patterns derived from a time series. We find that the permutation entropy based on the ordinal transition matrix outperforms the rest of the tested measures in discriminating the topological role of networked chaotic Rössler systems. Since the method is based on permutation entropy measures, it can be applied to arbitrary real-world time series exhibiting correlations originating from an existing underlying unknown network structure. In particular, we show the effectiveness of our method using experimental datasets of networks of nonlinear oscillators.

Deterministic and stochastic cooperation transitions in evolutionary games on networks.

Although the cooperative dynamics emerging from a network of interacting players has been exhaustively investigated, it is not yet fully understood when and how network reciprocity drives cooperation transitions. In this work, we investigate the critical behavior of evolutionary social dilemmas on structured populations by using the framework of master equations and Monte Carlo simulations. The developed theory describes the existence of absorbing, quasiabsorbing, and mixed strategy states and the transition nature, continuous or discontinuous, between the states as the parameters of the system change. In particular, when the decision-making process is deterministic, in the limit of zero effective temperature of the Fermi function, we find that the copying probabilities are discontinuous functions of the system's parameters and of the network degrees sequence. This may induce abrupt changes in the final state for any system size, in excellent agreement with the Monte Carlo simulation results. Our analysis also reveals the existence of continuous and discontinuous phase transitions for large systems as the temperature increases, which is explained in the mean-field approximation. Interestingly, for some game parameters, we find optimal "social temperatures" maximizing or minimizing the cooperation frequency or density.

Node differentiation dynamics along the route to synchronization in complex networks.

Synchronization has been the subject of intense research during decades mainly focused on determining the structural and dynamical conditions driving a set of interacting units to a coherent state globally stable. However, little attention has been paid to the description of the dynamical development of each individual networked unit in the process towards the synchronization of the whole ensemble. In this paper we show how in a network of identical dynamical systems, nodes belonging to the same degree class, differentiate in the same manner, visiting a sequence of states of diverse complexity along the route to synchronization independently on the global network structure. In particular, we observe, just after interaction starts pulling orbits from the initially uncoupled attractor, a general reduction of the complexity of the dynamics of all units being more pronounced in those with higher connectivity. In the weak-coupling regime, when synchronization starts to build up, there is an increase in the dynamical complexity, whose maximum is achieved, in general, first in the hubs due to their earlier synchronization with the mean field. For very strong coupling, just before complete synchronization, we found a hierarchical dynamical differentiation with lower degree nodes being the ones exhibiting the largest complexity departure. We unveil how this differentiation route holds for several models of nonlinear dynamics, including toroidal chaos and how it depends on the coupling function. This study provides insights to understand better strategies for network identification or to devise effective methods for network inference.

Complex networks exhibit intermittent synchronization.

The path toward the synchronization of an ensemble of dynamical units goes through a series of transitions determined by the dynamics and the structure of the connections network. In some systems on the verge of complete synchronization, intermittent synchronization, a time-dependent state where full synchronization alternates with non-synchronized periods, has been observed. This phenomenon has been recently considered to have functional relevance in neuronal ensembles and other networked biological systems close to criticality. We characterize the intermittent state as a function of the network topology to show that the different structures can encourage or inhibit the appearance of early signs of intermittency. In particular, we study the local intermittency and show how the nodes incorporate to intermittency in hierarchical order, which can provide information about the node topological role even when the structure is unknown.

Dynamical complexity measure to distinguish organized from disorganized dynamics.

We propose a metric to characterize the complex behavior of a dynamical system and to distinguish between organized and disorganized complexity. The approach combines two quantities that separately assess the degree of unpredictability of the dynamics and the lack of describability of the structure in the Poincaré plane constructed from a given time series. As for the former, we use the permutation entropy S_{p}, while for the latter, we introduce an indicator, the structurality Δ, which accounts for the fraction of visited points in the Poincaré plane. The complexity measure thus defined as the sum of those two components is validated by classifying in the (S_{p},Δ) space the complexity of several benchmark dissipative and conservative dynamical systems. As an application, we show how the metric can be used as a powerful biomarker for different cardiac pathologies and to distinguish the dynamical complexity of two electrochemical dissolutions.

High-order couplings in geometric complex networks of neurons.

We explore the consequences of introducing higher-order interactions in a geometric complex network of Morris-Lecar neurons. We focus on the regime where traveling synchronization waves are observed from a first-neighbors-based coupling to evaluate the changes induced when higher-order dynamical interactions are included. We observe that the traveling-wave phenomenon gets enhanced by these interactions, allowing the activity to travel further in the system without generating pathological full synchronization states. This scheme could be a step toward a simple phenomenological modelization of neuroglial networks.

Dynamical complexity as a proxy for the network degree distribution.

We explore the relation between the topological relevance of a node in a complex network and the individual dynamics it exhibits. When the system is weakly coupled, the effect of the coupling strength against the dynamical complexity of the nodes is found to be a function of their topological roles, with nodes of higher degree displaying lower levels of complexity. We provide several examples of theoretical models of chaotic oscillators, pulse-coupled neurons, and experimental networks of nonlinear electronic circuits evidencing such a hierarchical behavior. Importantly, our results imply that it is possible to infer the degree distribution of a network only from individual dynamical measurements.

Actualización sobre el manejo del tumor vasoproliferativo / Update on the management of vasoproliferative tumour

CASO CLÍNICO: Presentamos el caso de una paciente de 19 años con un tumor vasoproliferativo, en cuya evolución presentó una membrana epirretiniana, edema macular, hemovítreo y desprendimiento de retina exudativo. Se trató con 3 inyecciones intravítreas de bevacizumab, implante intravítreo de dexametasona, tocilizumab y 2 sesiones de crioterapia. DISCUSIÓN: Las opciones terapéuticas son: observación en los de menor tamaño, periféricos y sin amenaza para la visión. Si se necesita tratamiento, fotocoagulación con láser, crioterapia transconjuntival, inyecciones intravítreas de bevacizumab, termoterapia transpupilar, terapia fotodinámica, placas de radioterapia y cirugía son diferentes opciones disponibles. Recientemente se ha descrito que el tocilizumab y los implantes intravítreos de dexametasona pueden ser beneficiosos

CASE REPORT: Here we report a 19-year-old female patient who presented a vasoproliferative tumour. It caused complications, such as epiretinal membrane, macular oedema, vitreous haemorrhage, and exudative retinal detachment. The patient was treated with 3 injections of intravitreal bevacizumab, an intravitreal dexamethasone implant, tocilizumab, and double freeze-thaw cryotherapy. DISCUSSION: Therapeutic options are: observation, if it is small, if it is a peripheral lesion, and if there seems to be no threat to vision. If it requires treatment, laser photocoagulation, intravitreal bevacizumab, trans-conjunctival cryotherapy, transpupillary thermotherapy, photodynamic therapy, brachytherapy plaques and surgery are the different options available. Recently, tocilizumab and intravitreal dexamethasone implants have been reported to be beneficial

Relay synchronization in multiplex networks.

Relay (or remote) synchronization between two not directly connected oscillators in a network is an important feature allowing distant coordination. In this work, we report a systematic study of this phenomenon in multiplex networks, where inter-layer synchronization occurs between distant layers mediated by a relay layer that acts as a transmitter. We show that this transmission can be extended to higher order relay configurations, provided symmetry conditions are preserved. By first order perturbative analysis, we identify the dynamical and topological dependencies of relay synchronization in a multiplex. We find that the relay synchronization threshold is considerably reduced in a multiplex configuration, and that such synchronous state is mostly supported by the lower degree nodes of the outer layers, while hubs can be de-multiplexed without affecting overall coherence. Finally, we experimentally validated the analytical and numerical findings by means of a multiplex of three layers of electronic circuits.

Análisis de la relación entre habilidades cognitivas e hipoacusia sensorial severa unilateral / Analysis of the relationship between cognitive skills and unilateral sensory hearing loss

OBJETIVO: Analizar la asociación de competencias cognitivas en sujetos con hipoacusia unilateral severa versus sujetos con audición normal. MÉTODOS: Participaron 40 adultos; 20 pacientes, 10 de cada género, con hipoacusia unilateral sensorial severa y 20 sujetos sanos pareados al grupo de estudio. Las habilidades cognitivas se midieron con la batería Woodcock Muñoz-revisada y los procesos centrales auditivos con pruebas psicoacústicas monoaurales. Se realizaron gráficas de caja y prueba t de Student para muestras relacionadas con significación p ≤ 0,05. RESULTADOS: Al comparar el desempeño en las pruebas palabra filtrada y bisílabos comprimidos, se encontró diferencia estadísticamente significativa p ≤ 0,05, con mayor variabilidad de respuesta en los hipoacúsicos, los cuales también tuvieron mejor desempeño cognitivo en las subpruebas inversión de números, aprendizaje visual auditivo, análisis y síntesis, formación de conceptos y palabras incompletas. CONCLUSIONES: Los hipoacúsicos presentaron bajo desempeño en palabra filtrada y bisílabos comprimidos, y mayor habilidad para memoria, razonamiento y procesamiento auditivo. Es importante realizar pruebas complementarias, tales como procesos centrales auditivos y habilidades cognitivas que permitan establecer estrategias de habilitación, rehabilitación y terapéuticas con la finalidad de optimizar y estimular las habilidades de los sujetos con hipoacusia unilateral

OBJECTIVE: To analyse cognitive skills in patients with severe unilateral hearing loss versus those in subjects with normal hearing. METHODS: 40 adults participated: 20 patients (10 women and 10 men) with severe unilateral hearing loss and 20 healthy subjects matched to the study group. Cognitive abilities were measured with the Spanish version of the Woodcock Johnson Battery-Revised; central auditory processing was assessed with monaural psychoacoustic tests. Box plots were drawn and t tests were performed for samples with a significance of P≤.05. RESULTS: A comparison of performances on the filtered word testing and time-compressed disyllabic word tests between patients and controls revealed a statistically significant difference (P≤.05) with greater variability among responses by hearing impaired subjects. This same group also showed a better cognitive performance on the numbers reversed, visual auditory learning, analysis synthesis, concept formation, and incomplete words tests. CONCLUSIONS: Patients with hearing loss performed more poorly than controls on the filtered word and time-compressed disyllabic word tests, but more competently on memory, reasoning, and auditory processing tasks. Complementary tests, such as those assessing central auditory processes and cognitive ability tests, are important and helpful for designing habilitation/rehabilitation and therapeutic strategies intended to optimise and stimulate cognitive skills in subjects with unilateral hearing impairment

Emergent explosive synchronization in adaptive complex networks.

Adaptation plays a fundamental role in shaping the structure of a complex network and improving its functional fitting. Even when increasing the level of synchronization in a biological system is considered as the main driving force for adaptation, there is evidence of negative effects induced by excessive synchronization. This indicates that coherence alone cannot be enough to explain all the structural features observed in many real-world networks. In this work, we propose an adaptive network model where the dynamical evolution of the node states toward synchronization is coupled with an evolution of the link weights based on an anti-Hebbian adaptive rule, which accounts for the presence of inhibitory effects in the system. We found that the emergent networks spontaneously develop the structural conditions to sustain explosive synchronization. Our results can enlighten the shaping mechanisms at the heart of the structural and dynamical organization of some relevant biological systems, namely, brain networks, for which the emergence of explosive synchronization has been observed.

Update on the management of vasoproliferative tumour. / Actualización sobre el manejo del tumor vasoproliferativo.

CASE REPORT: Here we report a 19-year-old female patient who presented a vasoproliferative tumour. It caused complications, such as epiretinal membrane, macular oedema, vitreous haemorrhage, and exudative retinal detachment. The patient was treated with 3 injections of intravitreal bevacizumab, an intravitreal dexamethasone implant, tocilizumab, and double freeze-thaw cryotherapy. DISCUSSION: Therapeutic options are: observation, if it is small, if it is a peripheral lesion, and if there seems to be no threat to vision. If it requires treatment, laser photocoagulation, intravitreal bevacizumab, trans-conjunctival cryotherapy, transpupillary thermotherapy, photodynamic therapy, brachytherapy plaques and surgery are the different options available. Recently, tocilizumab and intravitreal dexamethasone implants have been reported to be beneficial.

Analysis of the relationship between cognitive skills and unilateral sensory hearing loss. / Análisis de la relación entre habilidades cognitivas e hipoacusia sensorial severa unilateral.

OBJECTIVE: To analyse cognitive skills in patients with severe unilateral hearing loss versus those in subjects with normal hearing. METHODS: 40 adults participated: 20 patients (10 women and 10 men) with severe unilateral hearing loss and 20 healthy subjects matched to the study group. Cognitive abilities were measured with the Spanish version of the Woodcock Johnson Battery-Revised; central auditory processing was assessed with monaural psychoacoustic tests. Box plots were drawn and t tests were performed for samples with a significance of P≤.05. RESULTS: A comparison of performances on the filtered word testing and time-compressed disyllabic word tests between patients and controls revealed a statistically significant difference (P≤.05) with greater variability among responses by hearing impaired subjects. This same group also showed a better cognitive performance on the numbers reversed, visual auditory learning, analysis synthesis, concept formation, and incomplete words tests. CONCLUSIONS: Patients with hearing loss performed more poorly than controls on the filtered word and time-compressed disyllabic word tests, but more competently on memory, reasoning, and auditory processing tasks. Complementary tests, such as those assessing central auditory processes and cognitive ability tests, are important and helpful for designing habilitation/rehabilitation and therapeutic strategies intended to optimise and stimulate cognitive skills in subjects with unilateral hearing impairment.

Inter-layer synchronization in non-identical multi-layer networks.

Inter-layer synchronization is a dynamical process occurring in multi-layer networks composed of identical nodes. This process emerges when all layers are synchronized, while nodes in each layer do not necessarily evolve in unison. So far, the study of such inter-layer synchronization has been restricted to the case in which all layers have an identical connectivity structure. When layers are not identical, the inter-layer synchronous state is no longer a stable solution of the system. Nevertheless, when layers differ in just a few links, an approximate treatment is still feasible, and allows one to gather information on whether and how the system may wander around an inter-layer synchronous configuration. We report the details of an approximate analytical treatment for a two-layer multiplex, which results in the introduction of an extra inertial term accounting for structural differences. Numerical validation of the predictions highlights the usefulness of our approach, especially for small or moderate topological differences in the intra-layer coupling. Moreover, we identify a non-trivial relationship connecting the betweenness centrality of the missing links and the intra-layer coupling strength. Finally, by the use of multiplexed layers of electronic circuits, we study the inter-layer synchronization as a function of the removed links.

Inter-layer synchronization in multiplex networks of identical layers.

Inter-layer synchronization is a distinctive process of multiplex networks whereby each node in a given layer evolves synchronously with all its replicas in other layers, irrespective of whether or not it is synchronized with the other units of the same layer. We analytically derive the necessary conditions for the existence and stability of such a state, and verify numerically the analytical predictions in several cases where such a state emerges. We further inspect its robustness against a progressive de-multiplexing of the network, and provide experimental evidence by means of multiplexes of nonlinear electronic circuits affected by intrinsic noise and parameter mismatch.

Effects of degree correlations on the explosive synchronization of scale-free networks.

We study the organization of finite-size, large ensembles of phase oscillators networking via scale-free topologies in the presence of a positive correlation between the oscillators' natural frequencies and the network's degrees. Under those circumstances, abrupt transitions to synchronization are known to occur in growing scale-free networks, while the transition has a completely different nature for static random configurations preserving the same structure-dynamics correlation. We show that the further presence of degree-degree correlations in the network structure has important consequences on the nature of the phase transition characterizing the passage from the phase-incoherent to the phase-coherent network state. While high levels of positive and negative mixing consistently induce a second-order phase transition, moderate values of assortative mixing, such as those ubiquitously characterizing social networks in the real world, greatly enhance the irreversible nature of explosive synchronization in scale-free networks. The latter effect corresponds to a maximization of the area and of the width of the hysteretic loop that differentiates the forward and backward transitions to synchronization.

Effective centrality and explosive synchronization in complex networks.

Synchronization of networked oscillators is known to depend fundamentally on the interplay between the dynamics of the graph's units and the microscopic arrangement of the network's structure. We here propose an effective network whose topological properties reflect the interplay between the topology and dynamics of the original network. On that basis, we are able to introduce the effective centrality, a measure that quantifies the role and importance of each network's node in the synchronization process. In particular, in the context of explosive synchronization, we use such a measure to assess the propensity of a graph to sustain an irreversible transition to synchronization. We furthermore discuss a strategy to induce the explosive behavior in a generic network, by acting only upon a fraction of its nodes.

Explosive synchronization in weighted complex networks.

The emergence of dynamical abrupt transitions in the macroscopic state of a system is currently a subject of the utmost interest. Given a set of phase oscillators networking with a generic wiring of connections and displaying a generic frequency distribution, we show how combining dynamical local information on frequency mismatches and global information on the graph topology suggests a judicious and yet practical weighting procedure which is able to induce and enhance explosive, irreversible, transitions to synchronization. We report extensive numerical and analytical evidence of the validity and scalability of such a procedure for different initial frequency distributions, for both homogeneous and heterogeneous networks, as well as for both linear and nonlinear weighting functions. We furthermore report on the possibility of parametrically controlling the width and extent of the hysteretic region of coexistence of the unsynchronized and synchronized states.