Spontaneous Synchronization Research Articles

Frequency-Specific Alterations of Local Synchronization in Idiopathic Generalized Epilepsy.

Recurrently and abnormally hypersynchronous discharge is a striking feature of idiopathic generalized epilepsy (IGE). Resting-state functional magnetic resonance imaging has revealed aberrant spontaneous brain synchronization, predominately in low-frequency range (<0.1 Hz), in individuals with IGE. Little is known, however, about these changes in local synchronization across different frequency bands. We examined alterations to frequency-specific local synchronization in terms of spontaneous blood oxygen level-dependent (BOLD) fluctuations across 5 bands, spanning 0 to 0.25 Hz. Specifically, we compared brain activity in a large cohort of IGE patients (n = 86) to age- and sex-matched normal controls (n = 86). IGE patients showed decreased local synchronization in low frequency (<0.073 Hz), primarily in the default mode network (DMN). IGE patients also exhibited increased local synchronization in high-frequency (>0.073 Hz) in a "conscious perception network," which is anchored by the pregenual and dorsal anterior cingulate cortex, as well as the bilateral insular cortices, possibly contributing to impaired consciousness. Furthermore, we found frequency-specific alternating local synchronization in the posterior portion of the DMN relative to the anterior part, suggesting an interaction between the disease and frequency bands. Importantly, the aberrant high-frequency local synchronization in the middle cingulate cortex was associated with disease duration, thus linking BOLD frequency changes to disease severity. These findings provide an overview of frequency-specific local synchronization of BOLD fluctuations, and may be helpful in uncovering abnormal synchronous neuronal activity in patients with IGE at specific frequency bands.

Intelligence-related differences in the asymmetry of spontaneous cerebral activity.

Recent evidence suggests the spontaneous BOLD signal synchronization of corresponding interhemispheric, homotopic regions as a stable trait of human brain physiology, with emerging differences in such organization being also related to some pathological conditions. To understand whether such brain functional symmetries play a role into higher-order cognitive functioning, here we correlated the functional homotopy profiles of 119 healthy subjects with their intelligence level. Counterintuitively, reduced homotopic connectivity in above average-IQ versus average-IQ subjects was observed, with significant reductions in visual and somatosensory cortices, supplementary motor area, rolandic operculum, and middle temporal gyrus, possibly suggesting that a downgrading of interhemispheric talk at rest could be associated with higher cognitive functioning. These regions also showed an increased spontaneous synchrony with medial structures located in ipsi- and contralateral hemispheres, with such pattern being mostly detectable for regions placed in the left hemisphere. The interactions with age and gender have been also tested, with different patterns for subjects above and below 25 years old and less homotopic connectivity in the prefrontal cortex and posterior midline regions in female participants with higher IQ scores. These findings support prior evidence suggesting a functional role for homotopic connectivity in human cognitive expression, promoting the reduction of synchrony between primary sensory regions as a predictor of higher intelligence levels.

Influence of Internal and External Noise on Spontaneous Visuomotor Synchronization

ABSTRACTHistorically, movement noise or variability is considered to be an undesirable property of biological motor systems. In particular, noise is typically assumed to degrade the emergence and stability of rhythmic motor synchronization. Recently, however, it has been suggested that small levels of noise might actually improve the functioning of motor systems and facilitate their adaptation to environmental events. Here, the authors investigated whether noise can facilitate spontaneous rhythmic visuomotor synchronization. They examined the influence of internal noise in the rhythmic limb movements of participants and external noise in the movement of an oscillating visual stimulus on the occurrence of spontaneous synchronization. By indexing the natural frequency variability of participants and manipulating the frequency variability of the visual stimulus, the authors demonstrated that both internal and external noise degrade synchronization when the participants’ and stimulus movement frequencies are similar, but can actually facilitate synchronization when the frequencies are different. Furthermore, the two kinds of noise interact with each other. Internal noise facilitates synchronization only when external noise is minimal and vice versa. Too much internal and external noise together degrades synchronization. These findings open new perspectives for better understanding the role of noise in human rhythmic coordination.

Firefly-inspired and robust time synchronization for cognitive radio ad hoc networks

Harnessing the full power of the paradigm-shifting cognitive radio ad hoc networks (CRAHNs) hinges on solving the problem of time synchronization between the radios on the different stages of the cognitive radio cycle. The dynamic network topology, the temporal and spatial variations in spectrum availability, and the distributed multi-hop architecture of CRAHNs mandate novel solutions to achieve time synchronization and efficiently support spectrum sensing, access, decision and mobility. In this article, we advance this research agenda by proposing the novel Bio-inspired time SynChronization protocol for CRAHNs (BSynC). The protocol draws on the spontaneous firefly synchronization observed in parts of Southeast Asia. The significance of BSynC lies in its capability of promoting symmetric time synchronization between pairs of network nodes independent of the network topology or a predefined sequence for synchronization. It enables the nodes in CRAHNs to efficiently synchronize in a decentralized manner, and it is also reliable to changes, faults and attacks. The findings suggest that BSynC improves convergence time, thereby favoring deployment in dynamic network scenarios.

Nonequilibrium inhomogeneous steady state distribution in disordered, mean-field rotator systems

We present a novel method to compute the phase space distribution in the nonequilibrium stationary state of a wide class of mean-field systems involving rotators subject to quenched disordered external drive and dissipation. The method involves a series expansion of the stationary distribution in inverse of the damping coefficient; the expansion coefficients satisfy recursion relations whose solution requires computing a matrix where about three quarters of the elements vanish, making numerical evaluation simple and efficient. We illustrate our method for the paradigmatic Kuramoto model of spontaneous collective synchronization and for its two mode generalization, in the presence of noise and inertia, and demonstrate an excellent agreement between simulations and theory for the phase space distribution.

Triggering extreme events at the nanoscale in photonic seas

Hurricanes, tsunamis, rogue waves and tornadoes are rare natural phenomena that embed an exceptionally large amount of energy, which appears and quickly disappears in a probabilistic fashion. This makes them difficult to predict and hard to generate on demand. Here we demonstrate that we can trigger the onset of rare events akin to rogue waves controllably, and systematically use their generation to break the diffraction limit of light propagation. We illustrate this phenomenon in the case of a random field, where energy oscillates among incoherent degrees of freedom. Despite the low energy carried by each wave, we illustrate how to control a mechanism of spontaneous synchronization, which constructively builds up the spectral energy available in the whole bandwidth of the field into giant structures, whose statistics is predictable. The larger the frequency bandwidth of the random field, the larger the amplitude of rare events that are built up by this mechanism. Our system is composed of an integrated optical resonator, realized on a photonic crystal chip. Through near-field imaging experiments, we record confined rogue waves characterized by a spatial localization of 206 nm and with an ultrashort duration of 163 fs at a wavelength of 1.55 μm. Such localized energy patterns are formed in a deterministic dielectric structure that does not require nonlinear properties. Rogue waves in a sea of photons can localize light beyond the diffraction limit, but their rarity makes them difficult to study. These events can now be controllably triggered in a photonic crystal resonator.

What would be Usain Bolt's 100-meter sprint world record without Tyson Gay? Unintentional interpersonal synchronization between the two sprinters.

Despite the desire of athletes to separate themselves from their competitors, to be faster or better, their performance is often influenced by those they are competing with. Here we show that the unintentional or spontaneous interpersonal synchronization of athletes' movements may partially account for such performance modifications. We examined the 100-m final of Usain Bolt in the 12th IAAF World Championship in Athletics (Berlin, 2009) in which he broke the world record, and demonstrate that Usain Bolt and Tyson Gay who ran side-by-side throughout the race spontaneously and intermittently synchronized their steps. This finding demonstrates that even the most optimized individual motor skills can be modulated by the simple presence of another individual via interpersonal coordination processes. It extends previous research by showing that the hard constraints of individual motor performance do not overwhelm the occurrence of spontaneous interpersonal synchronization and open promising new research directions for better understanding and improving athletic performance.

Mutual information as an order parameter for quantum synchronization

Spontaneous synchronization is a fundamental phenomenon, important in many theoretical studies and applications. Recently this effect has been analyzed and observed in a number of physical systems close to the quantum mechanical regime. In this work we propose the mutual information as a useful order parameter which can capture the emergence of synchronization in very different contexts, ranging from semi-classical to intrinsically quantum mechanical systems. Specifically we first study the synchronization of two coupled Van der Pol oscillators in both classical and quantum regimes and later we consider the synchronization of two qubits inside two coupled optical cavities. In all these contexts, we find that mutual information can be used as an appropriate figure of merit for determining the synchronization phases, independently of the specific details of the system.

Tempo and walking speed with music in the urban context.

The study explored the effect of music on the temporal aspects of walking behavior in a real outdoor urban setting. First, spontaneous synchronization between the beat of the music and step tempo was explored. The effect of motivational and non-motivational music (Karageorghis et al., 1999) on the walking speed was also studied. Finally, we investigated whether music can mask the effects of visual aspects of the walking route environment, which involve fluctuation of walking speed as a response to particular environmental settings. In two experiments, we asked participants to walk around an urban route that was 1.8 km in length through various environments in the downtown area of Hradec Králové. In Experiment 1, the participants listened to a musical track consisting of world pop music with a clear beat. In Experiment 2, participants were walking either with motivational music, which had a fast tempo and a strong rhythm, or with non-motivational music, which was slower, nice music, but with no strong implication to movement. Musical beat, as well as the sonic character of the music listened to while walking, influenced walking speed but did not lead to precise synchronization. It was found that many subjects did not spontaneously synchronize with the beat of the music at all, and some subjects synchronized only part of the time. The fast, energetic music increases the speed of the walking tempo, while slower, relaxing music makes the walking tempo slower. Further, it was found that listening to music with headphones while walking can mask the influence of the surrounding environment to some extent. Both motivational music and non-motivational music had a larger effect than the world pop music from Experiment 1. Individual differences in responses to the music listened to while walking that were linked to extraversion and neuroticism were also observed. The findings described here could be useful in rhythmic stimulation for enhancing or recovering the features of movement performance.

Spontaneous default mode network phase-locking moderates performance perceptions under stereotype threat.

This study assessed whether individual differences in self-oriented neural processing were associated with performance perceptions of minority students under stereotype threat. Resting electroencephalographic activity recorded in white and minority participants was used to predict later estimates of task errors and self-doubt on a presumed measure of intelligence. We assessed spontaneous phase-locking between dipole sources in left lateral parietal cortex (LPC), precuneus/posterior cingulate cortex (P/PCC), and medial prefrontal cortex (MPFC); three regions of the default mode network (DMN) that are integral for self-oriented processing. Results revealed that minorities with greater LPC-P/PCC phase-locking in the theta band reported more accurate error estimations. All individuals experienced less self-doubt to the extent they exhibited greater LPC-MPFC phase-locking in the alpha band but this effect was driven by minorities. Minorities also reported more self-doubt to the extent they overestimated errors. Findings reveal novel neural moderators of stereotype threat effects on subjective experience. Spontaneous synchronization between DMN regions may play a role in anticipatory coping mechanisms that buffer individuals from stereotype threat.

Tic related local field potentials in the thalamus and the effect of deep brain stimulation in Tourette syndrome: Report of three cases

ObjectiveThree patients with intractable Tourette syndrome (TS) underwent thalamic deep brain stimulation (DBS). To investigate the role of thalamic electrical activity in tic generation, local field potentials (LFP), EEG and EMG simultaneously were recorded. MethodsEvent related potentials and event related spectral perturbations of EEG and LFP, event related cross-coherences between EEG/LFP and LFP/LFP were analyzed. As time locking events, the tic onsets were used. Spontaneous tics were compared to voluntary tic mimicking. The effect of tic suppression and DBS on thalamic LFPs was evaluated. ResultsAll three patients showed time-locked and prior to onset of spontaneous motor tics thalamic synchronization and thalamo-cortical cross-coherence. Also in three patients, not time-locked to motor tics, increased intra-thalamic coherences in the 1–8Hz frequency band were found. In one patient it was demonstrated that voluntary mimicked tics were preceded by premotor cortical and thalamic potentials. In this patient unilateral thalamic DBS contralaterally decreased the background thalamic activity. ConclusionsThe present study in three cases with TS shows that spontaneous tics in TS are preceded by repetitive coherent thalamo-cortical discharges, indicating that preceding a tic the basal ganglia circuits are “charged up”, ultimately leading to a motor tic. SignificanceThalamic LFP recording may lead to more insight in underlying pathophysiological mechanisms in TS.

Spontaneous group synchronization of movements and respiratory rhythms.

We tested whether pre-assigned arm movements performed in a group setting spontaneously synchronized and whether synchronization extended to heart and respiratory rhythms. We monitored arm movements, respiration and electrocardiogram at rest and during spontaneous, music and metronome-associated arm-swinging. No directions were given on whether or how the arm swinging were to be synchronized between participants or with the external cues. Synchronization within 3 groups of 10 participants studied collectively was compared with pseudo-synchronization of 3 groups of 10 participants that underwent an identical protocol but in an individual setting. Motor synchronization was found to be higher in the collective groups than in the individuals for the metronome-associated condition. On a repetition of the protocol on the following day, motor synchronization in the collective groups extended to the spontaneous, un-cued condition. Breathing was also more synchronized in the collective groups than in the individuals, particularly at rest and in the music-associated condition. Group synchronization occurs without explicit instructions, and involves both movements and respiratory control rhythms.

140 Enteroids Derived From PERIOD2: LUCIFERASE Mice Autonomously Synchronize Circadian Rhythms Through a Steroid-Dependent Mechanism

Background&Aims:Circadian rhythms govern a wide array of intestinal epithelial functions in mammals, including nutrient absorption, microbial sensing, migration, and self-renewal. In the absence of coordinating signals generated by the central pacemaker activity of the suprachiasmatic nucleus, mammalian cells derived from peripheral tissues typically require an external cue such as a serum shock or steroid pulse to synchronize circadian rhythms in culture. Building on our recent finding of robust circadian rhythms in mouse small intestinal organoids (enteroids) derived from PERIOD2:LUCIFERASE (PER2:LUC) mice, we tested the capacity of PER2::LUC enteroids to synchronize circadian rhythms in the absence of these external cues.Methods:We generated PER2::LUC jejunal enteroids and maintained them in an incubating luminometer to measure real time oscillations of PER2 abundance. Enteroid experiments were performed under typical culture conditions in the presence or absence of MatrigelTM. Prior to bioluminescent recordings, populations of enteroids were subjected to a 2-hour 50% serum shock vs. a dexamethasone pulse to synchronize clock vs. no external synchronization. Separately, unsynchronized enteroids were incubated in the presence or absence of steroid receptor antagonist RU-486. Results: Serum-shocked and dexamethasone-treated enteroids displayed synchronized circadian rhythms of PER2 abundance immediately upon recording. The amplitude and persistence of these rhythms were increased in enteroids embedded in MatrigelTM vs. those suspended in media. In the absence of a serum shock or dexamethasone pulse, enteroids spontaneously developed synchronized circadian rhythms within 12 hours of recording. RU486 treatment prior to bioluminescent recording significantly delayed the onset of this spontaneous synchronization and dampened the amplitude of PER2 oscillations by 2to 6-fold. Conclusions: PERIOD2::LUCIFERASE enteroids autonomously synchronize circadian rhythms, providing further evidence of a tightly regulated peripheral clock intrinsic to the intestinal epithelium. Additional studies addressing the role of glucocorticoids in coordinating circadian rhythms in enteroids and in vivo should yield novel insights regarding circadian regulation of gut homeostasis and stem cell dynamics and pharmacologic effects of glucocorticoids on the intestinal epithelium.

141 Lactococcus Lactis CNCM I-1631 Targets Oxidative Stress to Ameliorate Inflammation in Early-Onset Experimental Colitis

Background&Aims:Circadian rhythms govern a wide array of intestinal epithelial functions in mammals, including nutrient absorption, microbial sensing, migration, and self-renewal. In the absence of coordinating signals generated by the central pacemaker activity of the suprachiasmatic nucleus, mammalian cells derived from peripheral tissues typically require an external cue such as a serum shock or steroid pulse to synchronize circadian rhythms in culture. Building on our recent finding of robust circadian rhythms in mouse small intestinal organoids (enteroids) derived from PERIOD2:LUCIFERASE (PER2:LUC) mice, we tested the capacity of PER2::LUC enteroids to synchronize circadian rhythms in the absence of these external cues.Methods:We generated PER2::LUC jejunal enteroids and maintained them in an incubating luminometer to measure real time oscillations of PER2 abundance. Enteroid experiments were performed under typical culture conditions in the presence or absence of MatrigelTM. Prior to bioluminescent recordings, populations of enteroids were subjected to a 2-hour 50% serum shock vs. a dexamethasone pulse to synchronize clock vs. no external synchronization. Separately, unsynchronized enteroids were incubated in the presence or absence of steroid receptor antagonist RU-486. Results: Serum-shocked and dexamethasone-treated enteroids displayed synchronized circadian rhythms of PER2 abundance immediately upon recording. The amplitude and persistence of these rhythms were increased in enteroids embedded in MatrigelTM vs. those suspended in media. In the absence of a serum shock or dexamethasone pulse, enteroids spontaneously developed synchronized circadian rhythms within 12 hours of recording. RU486 treatment prior to bioluminescent recording significantly delayed the onset of this spontaneous synchronization and dampened the amplitude of PER2 oscillations by 2to 6-fold. Conclusions: PERIOD2::LUCIFERASE enteroids autonomously synchronize circadian rhythms, providing further evidence of a tightly regulated peripheral clock intrinsic to the intestinal epithelium. Additional studies addressing the role of glucocorticoids in coordinating circadian rhythms in enteroids and in vivo should yield novel insights regarding circadian regulation of gut homeostasis and stem cell dynamics and pharmacologic effects of glucocorticoids on the intestinal epithelium.

Spontaneous synchronization in large pendulum arrays

Experiments on mechanical oscillator arrays show that complete inphase synchronization can emerge in a matter of minutes, even for fairly large arrays started from random initial conditions. At the same time, one expects complete inphase synchronization to become increasingly difficult to observe as array size grows. We explore the conditions under which inphase synchronization prevails with the help of a simple, somewhat stylized, iterative map model which embodies the problem’s key dynamical features.

Impact of network topology on synchrony of oscillatory power grids

Replacing conventional power sources by renewable sources in current power grids drastically alters their structure and functionality. The resulting grid will be far more decentralized with an distinctly different topology. Here we analyze the impact of grid topologies on spontaneous synchronization, considering regular, random and small-world topologies and focusing on the influence of decentralization. We employ the classic model of power grids modeling consumers and sources as second order oscillators. We first analyze the global dynamics of the simplest non-trivial (two-node) network that exhibit a synchronous (normal operation) state, a limit cycle (power outage) and coexistence of both. Second, we estimate stability thresholds for the collective dynamics of small network motifs, in particular star-like networks and regular grid motifs. For larger networks we numerically investigate decentralization scenarios finding that decentralization itself may support power grids in reaching stable synchrony for lower lines transmission capacities. Decentralization may thus be beneficial for power grids, regardless of their special resulting topology. Regular grids exhibit a specific transition behavior not found for random or small-world grids.

Dynamics of Bec Mixtures Loaded into the Optical Lattice in the Presence of Linear Inter-Component Coupling

We consider dynamics of a two-component Bose–Einstein condensate, where the components correspond to different hyperfine states of the same sort of atoms. External microwave radiation leads to resonant transitions between the states. The condensate is loaded into the optical lattice. We invoke the tight-binding approximation and examine the interplay of spatial and internal dynamics of the mixture. We show that internal dynamics qualitatively depends on the intra-component interaction strength and the phase configuration of the initial state. We focus attention on two intriguing phenomena occurring at certain values of the parameters. The first phenomenon is the spontaneous synchronization of Rabi oscillations running inside neighboring lattice sites. The other one is demixing of the condensate with formation of immiscible solitons at sufficiently strong nonlinearity. Demixing is preceded by the transient regime with highly irregular behavior of the mixture.

The effect of instruction to synchronize over step frequency while walking with auditory cues on a treadmill

Walking to a pacing stimulus has proven useful in motor rehabilitation, and it has been suggested that spontaneous synchronization could be preferable to intentional synchronization. But it is still unclear if the paced walking effect can occur spontaneously, or if intentionality plays a role. The aim of this work is to analyze the effect of sound pacing on gait with and without instruction to synchronize, and with different rhythmic auditory cues, while walking on a treadmill.Firstly, the baseline step frequency while walking on a treadmill was determined for all participants, followed by experimental sessions with both music and footstep sound cues. Participants were split into two groups, with one being instructed to synchronize their gait to the auditory stimuli, and the other being simply told to walk. Individual auditory cues were generated for each participant: for each trial, cues were provided at the participant’s baseline walking frequency, at 5% and 10% above baseline, and at 5% and 10% below baseline.This study’s major finding was the role of intention on synchronization, given that only the instructed group synchronized their gait with the auditory cues. No differences were found between the effects of step or music stimuli on step frequency.In conclusion, without intention or cues that direct the individual’s attention, spontaneous gait synchronization does not occur during treadmill walking.

Spontaneous Synchronization in Two Mutually Coupled Memristor-Based Chua’s Circuits: Numerical Investigations

Chaotic dynamics of numerous memristor-based circuits is widely reported in literature. Recently, some works have appeared which study the problem of synchronization control of these systems in a master-slave configuration. In the present paper, the spontaneous dynamic behavior of two chaotic memristor-based Chua’s circuits, mutually interacting through a coupling resistance, was studied via computer simulations in order to study possible self-organized synchronization phenomena. The used memristor is a flux controlled memristor with a cubic nonlinearity, and it can be regarded as a time-varying memductance. The memristor, in effect, retains memory of its past dynamic and any difference in the initial conditions of the two circuits results in different values of the corresponding memductances. In this sense, due to the memory effect of the memristor, even if coupled circuits have the same parameters they do not constitute two completely identical chaotic oscillators. As is known, for nonidentical chaotic systems, in addition to complete synchronizations (CS) other weaker forms of synchronization which provide correlations between the signals of the two systems can also occur. Depending on initial conditions and coupling strength, both chaotic and nonchaotic synchronization are observed for the system considered in this work.

Spontaneous Synchronization of Eyeblinks during Story-Telling Performance

Spontaneous Synchronization of Eyeblinks during Story-Telling Performance