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Phase Synchronization (phase + synchronization)
Selected AbstractsUnusual synchronization of Red Sea fish energy expendituresECOLOGY LETTERS, Issue 2 2003Lewi Stone Abstract The highly gregarious goat fish Parupeneus forskalii found in the Red Sea at Eilat, Israel exhibit highly synchronous swimming and feeding activity. Five fish were studied under controlled conditions and highly resolved time-series of their energy expenditures were measured. All fish demonstrated strong phase synchronization in that their activity levels, although erratic in time and intensity, were collectively coordinated and peaked simultaneously together. The synchronization of these wildly varying, and possibly chaotic signals of energy expenditures, were quantified using phase analysis. We suggest that, ecologically, this collective synchronization is a strategy that increases food-catch. [source] Typical versus Atypical Absence Seizures: Network Mechanisms of the Spread of ParoxysmsEPILEPSIA, Issue 8 2007Jose L. Perez Velazquez Summary: Purpose: Typical absence seizures differ from atypical absence seizures in terms of semiology, EEG morphology, network circuitry, and cognitive outcome, yet have the same pharmacological profile. We have compared typical to atypical absence seizures, in terms of the recruitment of different brain areas. Our initial question was whether brain areas that do not display apparent paroxysmal discharges during typical absence seizures, are affected during the ictal event in terms of synchronized activity, by other, distant areas where seizure activity is evident. Because the spike-and-wave paroxysms in atypical absence seizures invade limbic areas, we then asked whether an alteration in inhibitory processes in hippocampi may be related to the spread seizure activity beyond thalamocortical networks, in atypical seizures. Methods: We used two models of absence seizures in rats: one of typical and the other of atypical absence seizures. We estimated phase synchronization, and evaluated inhibitory transmission using a paired-pulse paradigm. Results: In typical absence seizures, we observed an increase in synchronization between hippocampal recordings when spike-and-wave discharges occurred in the cortex and thalamus. This indicates that seizure activity in the thalamocortical circuitry enhances the propensity of limbic areas to synchronize, but is not sufficient to drive hippocampal circuitry into a full paroxysmal discharge. Lower paired-pulse depression was then found in hippocampus of rats that displayed atypical absence seizures. Conclusions: These observations suggest that circuitries in brain areas that do not display apparent seizure activity become synchronized as seizures occur within thalamocortical circuitry, and that a weakened hippocampal inhibition may predispose to develop synchronization into full paroxysms during atypical absence seizures. [source] Dynamic links between theta executive functions and alpha storage buffers in auditory and visual working memoryEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2010Masahiro Kawasaki Abstract Working memory (WM) tasks require not only distinct functions such as a storage buffer and central executive functions, but also coordination among these functions. Neuroimaging studies have revealed the contributions of different brain regions to different functional roles in WM tasks; however, little is known about the neural mechanism governing their coordination. Electroencephalographic (EEG) rhythms, especially theta and alpha, are known to appear over distributed brain regions during WM tasks, but the rhythms associated with task-relevant regional coupling have not been obtained thus far. In this study, we conducted time,frequency analyses for EEG data in WM tasks that include manipulation periods and memory storage buffer periods. We used both auditory WM tasks and visual WM tasks. The results successfully demonstrated function-specific EEG activities. The frontal theta amplitudes increased during the manipulation periods of both tasks. The alpha amplitudes increased during not only the manipulation but also the maintenance periods in the temporal area for the auditory WM and the parietal area for the visual WM. The phase synchronization analyses indicated that, under the relevant task conditions, the temporal and parietal regions show enhanced phase synchronization in the theta bands with the frontal region, whereas phase synchronization between theta and alpha is significantly enhanced only within the individual areas. Our results suggest that WM task-relevant brain regions are coordinated by distant theta synchronization for central executive functions, by local alpha synchronization for the memory storage buffer, and by theta,alpha coupling for inter-functional integration. [source] Dissociated theta phase synchronization in amygdalo- hippocampal circuits during various stages of fear memoryEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2007Rajeevan T. Narayanan Abstract The amygdala and the hippocampus are critically involved in the formation and retention of fear memories. However, their precise contribution to, and their interplay during, fear memory formation are not fully understood. In the present study we investigated network activities in the amygdalo-hippocampal system of freely behaving mice at different stages of fear memory consolidation and retention. Our data show enhanced theta phase synchronization in this pathway during the retrieval of fear memory at long-term (24 h post-training), but not short-term (2 min, 30 min and 2 h post-training) stages, following both contextual and auditory cued conditioning. However, retrieval of remotely conditioned fear (30 days post-training) failed to induce an increase in synchronization despite there still being memory retention. Thus, our data indicate that the amygdalo-hippocampal interaction reflects a dynamic interaction of ensemble activities related to various stages of fear memory consolidation and/or retention, and support the notion that recent and remote memories are organized through different network principles. [source] Characterizing instantaneous phase relationships in whole-brain fMRI activation dataHUMAN BRAIN MAPPING, Issue 2 2002Angela R. Laird Abstract Typically, fMRI data is processed in the time domain with linear methods such as regression and correlation analysis. We propose that the theory of phase synchronization may be used to more completely understand the dynamics of interacting systems, and can be applied to fMRI data as a novel method of detecting activation. Generalized synchronization is a phenomenon that occurs when there is a nonlinear functional relationship present between two or more coupled, oscillatory systems, whereas phase synchronization is defined as the locking of the phases while the amplitudes may vary. In this study, we developed an application of phase synchronization analysis that is appropriate for fMRI data, in which the phase locking condition is investigated between a voxel time series and the reference function of the task performed. A synchronization index is calculated to quantify the level of phase locking, and a nonparametric permutation test is used to determine the statistical significance of the results. We performed the phase synchronization analysis on the data from five volunteers for an event-related finger-tapping task. Functional maps were created that provide information on the interrelations between the instantaneous phases of the reference function and the voxel time series in a whole-brain fMRI activation data set. We conclude that this method of analysis is useful for revealing additional information on the complex nature of the fMRI time series. Hum. Brain Mapping 16:71,80, 2002. © 2002 Wiley-Liss, Inc. [source] Gamma band activity and its synchronization reflect the dysfunctional emotional processing in alexithymic personsPSYCHOPHYSIOLOGY, Issue 6 2006Atsushi Matsumoto Abstract In the present study, we investigated the gamma band response and its phase synchrony between electrodes in alexithymia, which is characterized by a disability in identifying and describing feelings. Individuals with high and low alexithymia scores were selected according to the scores on the 20-item Toronto Alexithymia Scale. EEG was recorded from alexithymic and nonalexithymic persons viewing emotionally negative or neutral stimuli. Nonalexithymic persons exhibited increased gamma band power and phase synchronization at the 400,450-ms time window when processing emotionally negative stimuli. Neither enhanced gamma band power nor phase synchronization was observed in alexithymic persons in the negative emotion condition. These results suggest that gamma band activity reflects emotional processing, and alexithymic persons may have a deficit in communication between brain regions or in the utilization of memory or emotional information during the processing of emotional stimuli. [source] | ||||||||||