Temporal evolution of coherence and power in the human sleep electroencephalogram

Coherence analysis of the human sleep electroencephalogram (EEG) was used to investigate relations between brain regions. In all-night EEG recordings from eight young subjects, the temporal evolution of power and coherence spectra within and between cerebral hemispheres was investigated from bipolar derivations along the antero-posterior axis. Distinct peaks in the power and coherence spectra were present in NREM sleep but not in REM sleep. They were situated in the frequency range of sleep spindles (13–14 Hz), alpha band (9–10 Hz) and low delta band (1–2 Hz). Whereas the peaks coincided in the power and coherence spectra, a dissociation of their temporal evolution was observed. In the low delta band, only power but not coherence showed a decline across successive NREM sleep episodes. Moreover, power increased gradually in the first part of a NREM sleep episode, whereas coherence showed a rapid rise. The results indicate that the intrahemispheric and interhemispheric coherence of EEG activity attains readily a high level in NREM sleep and is largely independent of the signal amplitude.     

Recording and spectrum analysis of the planarian electroencephalogram

Many animals produce continuous brainwaves, known as the electroencephalogram (EEG), but it is not known at what point in evolution the EEG developed. Planarians possess the most primitive form of brain, but still exhibit learning and memory behaviors. Here, we observed and characterized the EEG waveform of the planarian. We inserted a monopole electrode into the head of a planarian on a cold stage, and were able to observe the EEG at sub-microvolt amplitudes. The EEG had a continuous waveform, similar to that of evolutionarily advanced animals with more developed brains. Occasional myogenic potential spikes were observed in the EEG due to sticking of the electrode, but this was markedly diminished by cooling the sample, which enabled us to investigate the intrinsic character of the continuous EEG waveform.     

Cortico-cortical phase synchrony in auditory mismatch processing

Previous studies have shown a reduced MMN in patients with lesions in the temporal or frontal lobes, suggesting a temporal-frontal involvement in change detection. However, how the temporal lobe interacts with other brain areas in responding to unexpected deviant stimuli remains unclear. This study aimed to evaluate the functional connectivity between cerebral regions by measuring the phase synchrony of magnetoencephalographic (MEG) signals elicited by regular simple tones and their duration-deviants in an oddball paradigm. We measured MEG responses to deviant (1000-Hz frequency, 50-ms duration, probability of 15%) and standard (1000-Hz frequency, 100-ms duration) sounds in 10 healthy adults. By using the Morlet wavelet-based analysis, relative phase synchronization values of 4-40 Hz MEG responses at 150-300 ms after stimulus onset were calculated with respect to a reference channel from the temporal region. Phase synchronization was clearly identified between the temporal and ipsilateral frontal region in the auditory evoked responses. This temporal-frontal synchronization was significantly larger in deviants-elicited than standards-elicited activation at 4-25 Hz in the left hemisphere (p < 0.05), and at 4-8 Hz in the right hemisphere (p < 0.01). Also, temporal-temporal and temporal-parietal phase synchronies were found in deviants-evoked 4-8 Hz responses.The present results suggest an involvement of temporal-temporal, temporal-frontal, and temporal-parietal neuronal network in detecting auditory change. Phase synchronization analysis may provide a useful window to further understanding of the cerebral reactivity during the processing of auditory deviants.     

Reliability of event‐related EEG functional connectivity during visual entrainment: Magnitude squared coherence and phase synchrony estimates

There is an increasing trend towards using noninvasive electroencephalography (EEG) to quantify functional brain connectivity. However, little is known about the psychometrics of commonly used functional connectivity indices. We examined the internal consistency of two different connectivity metrics: magnitude squared coherence and phase synchrony. EEG was recorded during visual entrainment to elicit a strong oscillatory component of known frequency. We found acceptable to good split‐half reliability for the connectivity metrics when computing all possible pairwise interactions and after selecting an a priori seed reference. We also compared reliability estimates when using average referenced sensor versus reference independent current source density EEG data. Additional considerations were given to determining how reliability was influenced by factors including trial number, signal‐to‐noise ratio, and frequency content.     

Motor-unit coherence and its relation with synchrony are influenced by training

The purpose of the study was to quantify the strength of motor-unit coherence from the left and right first dorsal interosseous muscles in untrained, skill-trained (musicians), and strength-trained (weightlifters) individuals who had long-term specialized use of their hand muscles. The strength of motor-unit coherence was quantified from a total of 394 motor-unit pairs in 13 subjects using data from a previous study in which differences were found in the strength of motor-unit synchronization depending on training status. In the present study, we found that the strength of motor-unit coherence was significantly greater in the left compared with the right hand of untrained right-handed subjects with the largest differences observed between 21 and 24 Hz. The strength of motor-unit coherence was lower in both hands of skill-trained subjects (21-27 Hz) and the right (skilled) hand of untrained subjects (21-24 Hz), whereas the largest motor-unit coherence was observed in both hands of strength-trained subjects (3-9 and 21-27 Hz). A strong curvilinear association was observed between motor-unit synchronization and the integral of coherence at 10-30 Hz in all motor-unit pairs (r2 = 0.77), and was most pronounced in strength-trained subjects (r2 = 0.90). Furthermore, this association was accentuated when using synchronization data with broad peaks (>11 ms), suggesting that the 10- to 30-Hz coherence is due to oscillatory activity in indirect branched common inputs. The altered coherence with training may be due to an interaction between cortical inhibition and the number of direct common inputs to motor neurons in skill- or strength-trained hands.     

A spatial power spectrum analysis of the electroencephalogram

Summary The method of spatial power-spectrum analysis has been applied to measurements of the distribution of rms alpha-band potential on the scalp. Data was recorded using the 31-Electrode System and spatial power-spectrum estimates (PSEs) were obtained from Mercator projections of the potential interpolated using the triangular method. PSEs were calculated using the Lim and Malik algorithm for maximum-entropy power-spectrum estimation. In order to investigate the utility of spatial power-spectrum analysis, PSEs were obtained from subjects in two conditions; resting with eyes closed (EC) and resting with eyes open and fixed on a single point (EO). A stepwise discriminant analysis was performed with features from the PSEs and the resultant discriminant function was applied to data not considered in the formulation of the function. Over 92% of test data was correctly classified. The features used in the discriminant function identify spatial waves which are most useful in separating data. The results demonstrate that waves oriented along front-back and right-left lines are most important in separating data into EC and EO groups.Acknowledgements: The financial support provided by the Alberta Heritage Foundation for Medical Research (in the form of a Studentship (RBP)) and by the National Health Research and Development Program of the Government of Canada is gratefully acknowledged.     

Interhemispheric coherence of the sleep electroencephalogram in mice with congenital callosal dysgenesis

Regional differences in the effect of sleep deprivation on the sleep electroencephalogram (EEG) may be related to interhemispheric synchronization. To investigate the role of the corpus callosum in interhemispheric EEG synchronization, coherence spectra were computed in mice with congenital callosal dysgenesis (B1) under baseline conditions and after 6-h sleep deprivation, and compared with the spectra of a control strain (C57BL/6). In B1 mice coherence was lower than in controls in all vigilance states. The level of coherence in each of the three totally acallosal mice was lower than in the mice with only partial callosal dysgenesis. The difference between B1 and control mice was present over the entire 0.5-25 Hz frequency range in non-rapid eye movement sleep (NREM sleep), and in all frequencies except for the high delta and low theta band (3-7 Hz) in rapid eye movement (REM) sleep and waking. In control mice, sleep deprivation induced a rise of coherence in the Delta band of NREM sleep in the first 2 h of recovery. This effect was absent in B1 mice with total callosal dysgenesis and attenuated in mice with partial callosal dysgenesis. In both strains the effect of sleep deprivation dissipated within 4 h. The results show that EEG synchronization between the hemispheres in sleep and waking is mediated to a large part by the corpus callosum. This applies also to the functional changes induced by sleep deprivation in NREM sleep. In contrast, interhemispheric synchronisation of theta oscillations in waking and REM sleep may be mediated by direct interhippocampal connections.     

Measurement of phase synchrony of coupled segmentation clocks

The temporal behavior of segmentation clock oscillations shows phase synchrony via mean field like coupling of delta protein restricting to nearest neighbors only, in a configuration of cells arranged in a regular three dimensional array. We found the increase of amplitudes of oscillating dynamical variables of the cells as the activation rate of delta-notch signaling is increased, however, the frequencies of oscillations are decreased correspondingly. Our results show the phase transition from desynchronized to synchronized behavior by identifying three regimes, namely, desynchronized, transition and synchronized regimes supported by various qualitative and quantitative measurements.     

Hippocampo–cerebellar theta band phase synchrony in rabbits

Hippocampal functioning, in the form of theta band oscillation, has been shown to modulate and predict cerebellar learning of which rabbit eyeblink conditioning is perhaps the most well-known example. The contribution of hippocampal neural activity to cerebellar learning is only possible if there is a functional connection between the two structures. Here, in the context of trace eyeblink conditioning, we show (1) that, in addition to the hippocampus, prominent theta oscillation also occurs in the cerebellum, and (2) that cerebellar theta oscillation is synchronized with that in the hippocampus. Further, the degree of phase synchrony (PS) increased both as a response to the conditioning stimuli and as a function of the relative power of hippocampal theta oscillation. However, the degree of PS did not change as a function of either training or learning nor did it predict learning rate as the hippocampal theta ratio did. Nevertheless, theta band synchronization might reflect the formation of transient neural assemblies between the hippocampus and the cerebellum. These findings help us understand how hippocampal function can affect eyeblink conditioning, during which the critical plasticity occurs in the cerebellum. Future studies should examine cerebellar unit activity in relation to hippocampal theta oscillations in order to discover the detailed mechanisms of theta-paced neural activity.     

Reduced degree of long-range phase synchrony in pathological human brain

In this paper multivariate spontaneous EEG signals from three broad groups of human subjects--control, seizure, and mania--were studied with the aim of investigating the possible effect of these pathologies on the degree of phase synchronization between cortical areas. The degree of phase synchrony was measured by two recently developed measures which are more suitable than classical indices like correlation or coherence when dealing with nonlinear and non-stationary signals like the EEG. Signals were reduced to seven frequency bands (delta, theta, alpha-1, alpha-2, beta-1, beta-2 and gamma) which were statistically compared between the normal and the other two groups. It was found that the degree of long-range synchrony was significantly reduced for both pathological groups as compared with the control group. No clear differences were found in the degrees of short-range synchrony.     

Brain temperature dependent changes in the electroencephalogram power spectrum of humans and animals

In animals, changes in brain temperature induce a shift in frequencies in the electroencephalogram (EEG). Given the large decreases in body and brain temperature that occur during hibernation, putative functions that were previously ascribed to certain EEG frequencies are no longer valid because of the progressive shift away from the original frequency. In the present review it is proposed that even moderate temperature changes in humans and animals, such as those across the circadian or menstrual cycle, or induced by drugs, have a significant effect on EEG frequencies and the corresponding power spectrum. Alterations in the relative EEG power spectrum, in studies where body temperature also changes, may not be a direct cause of the treatment under investigation, but a consequence of effects on body or brain temperature. However, these effects on the EEG power spectrum are usually interpreted to result directly from the experimental treatment.     

Semantic priming increases left hemisphere theta power and intertrial phase synchrony

Information is stored in distributed cortical networks, but it is unclear how distributed stores are synthesized into a unified percept. Activation of local circuits in the gamma range (30 < < 80 Hz), and distributed stores in the low theta range (3–5 Hz) may underlie perceptual binding. Words have a crucial role in semantic memory. Within memory, the activation of distributed semantic stores is facilitated by conceptually related previous items, termed semantic priming. We sought to detect event‐related brain oscillations (EROs) sensitive to semantic activation and priming. Here, we show that low theta evoked power and intertrial phase locking (4–5 Hz) from 250–350 msec over left hemisphere language areas was greater to related than to unrelated words. Theta band event‐related oscillations over left hemisphere language areas may provide a brain signature for semantic activation across distributed stores being facilitated by semantic priming.     

Loss of phase synchrony in an animal model of partial status epilepticus

Interrupting a focal, chronic infusion of GABA to the rat motor cortex initiates the progressive emergence of a sustained spiking electroencephalographic (EEG) activity, associated with myoclonic jerks of the corresponding body territory. This activity is maintained over several hours, has an average frequency of 1.5 Hz, is localized to the infusion site and never generalizes. The GABA withdrawal syndrome (GWS) has therefore features of partial status epilepticus. Changes in EEG signals associated with the GWS were studied in freely moving rats by measuring the phase synchrony between bilateral epidural records from the neocortex. Our results showed (i) epileptic activity was associated with a striking decrease in phase synchrony between all pairs of electrodes including the focus, predominantly in the 1-6 Hz frequency range. There was a mean decrease of 75.34+/-5.26% in phase synchrony levels between the period before GABA interruption and the period after epileptic activity appeared. (ii) This reduction in synchrony contrasted with an increase of power spectral density in the corresponding EEG channels over the same 1-6 Hz frequency range, (iii) neither changes in synchrony nor in nonlinear dynamics were detected before the first EEG spikes, (iv) systemic injection of ketamine, an antagonist of N-methyl-d-aspartic acid (NMDA) receptors, modified transiently both epileptic activity and the synchrony profile. (v) Spiking activity and synchrony changes were suppressed by reperfusion of GABA. Our data suggest that, during a partial status epilepticus, interactions between the epileptic focus and connected neocortical neuronal populations are dramatically decreased in low frequencies.     

Amplitude and phase relationship between alpha and beta oscillations in the human electroencephalogram

The relationship between the electro-encephalographic (EEG) alpha and beta oscillations in the resting condition was investigated in the study. EEGs were recorded in 33 subjects, and alpha (7.5–12.5 Hz) and beta (15–25 Hz) oscillations were extracted with the use of a modified wavelet transform. Power, peak frequency and phase synchronisation were evaluated for both types of oscillation. The average beta—alpha peak frequency ratio was about 1.9–2.0 for all electrode derivations. The peak frequency of beta activity was within 70–90% of the 95% confidence interval of twice the alpha frequency. A significant (p<0.05) linear regression was found between beta and alpha power in all derivations in 32 subjects, with the slope of the regression line being ≈0.3. There was no significant difference in the slope of the line in different electrode locations, although the power correlation was strongest in the occipital locations where alpha and beta oscillations had the largest power. A significant 1∶2 phase synchronisation was present between the alpha and beta oscillations, with a phase lag of about Π/2 in all electrode derivations. The strong frequency relationship between the resting beta and alpha oscillations suggests that they are generated by a common mechanism. Power and phase relationships were weaker, suggesting that these properties can be modulated by additional mechanisms as well as be influenced by noise. A careful distinction between alpha-dependent and alpha-independent beta activity should be considered when making statements about the possible significance of genuine beta activity in different neurophysiological mechanisms.     

海马区神经电信号相位同步化的初步研究

大脑各个区域的神经电活动存在各种不同频率的振荡,而theta节律振荡(5～10 Hz)是海马区神经活动具有代表性的特征.本文用海马区theta节律显著性检测和theta节律相位同步化的方法来分析多电极记录的神经元放电及其局部场电位信号,验证了theta节律成分的显著性和动物行为之间的关系,并首次研究了小鼠在不同行为状态下左右海马神经电活动之间的相位同步化的差异.     

Brain coordination dynamics: true and false faces of phase synchrony and metastability

Understanding the coordination of multiple parts in a complex system such as the brain is a fundamental challenge. We present a theoretical model of cortical coordination dynamics that shows how brain areas may cooperate (integration) and at the same time retain their functional specificity (segregation). This model expresses a range of desirable properties that the brain is known to exhibit, including self-organization, multi-functionality, metastability and switching. Empirically, the model motivates a thorough investigation of collective phase relationships among brain oscillations in neurophysiological data. The most serious obstacle to interpreting coupled oscillations as genuine evidence of inter-areal coordination in the brain stems from volume conduction of electrical fields. Spurious coupling due to volume conduction gives rise to zero-lag (inphase) and antiphase synchronization whose magnitude and persistence obscure the subtle expression of real synchrony. Through forward modeling and the help of a novel colorimetric method, we show how true synchronization can be deciphered from continuous EEG patterns. Developing empirical efforts along the lines of continuous EEG analysis constitutes a major response to the challenge of understanding how different brain areas work together. Key predictions of cortical coordination dynamics can now be tested thereby revealing the essential modus operandi of the intact living brain.     

Breathing pattern alterations with aerosolized buffered saline--effects of topical airway anesthesia

Bronchoconstriction, measured by spirometry and body plethysmography, may occur with inhalation of aerosolized buffered saline (ABS) (0.5% sodium chloride and phosphate buffer) in asymptomatic patients with bronchial asthma. To estimate the prevalence and mechanism of this phenomenon, we employed continuous non-invasive monitoring of the breathing pattern to estimate changes of end-expiratory level, minute ventilation and mean inspiratory flow, which may be more sensitive albeit less specific indicators of bronchoconstriction. We studied normal and asymptomatic asthmatic subjects before and after ABS inhalation. Deep breaths of ABS had no effect on the breathing pattern in normals, but in all of the asthmatics increases of end-expiratory level, minute ventilation, tidal volume and mean inspiratory flow lasted at least 15 minutes. On another day, prior topical airway anesthesia in the asthmatic subjects prevented the changes in breathing pattern after ABS inhalation. Thus analysis of the breathing pattern suggests that bronchoconstriction or irritation of vagal airway receptors after inhalation of aerosolized buffered saline occurs to a high degree in asymptomatic asthmatic subjects because changes in breathing pattern are prevented by prior airway anesthesia which probably inactivates vagal afferent pathways.     

Tobacco-induced alterations to the Fourier-transform infrared spectrum of serum

Infrared (IR) spectroscopy can distinguish differences in the characteristics of diverse molecules by using infrared radiation to probe chemical bonds. Consequently, alterations to the molecular characteristics of tissues and body fluids that help define specific pathological processes and conditions can be identified by IR spectroscopy. This study analyzed the molecular spectrum of cotinine by IR spectroscopy and determined tobacco-induced alterations to the IR profile of serum to establish whether these alterations can differentiate smokers and nonsmokers. The IR spectra of serum samples obtained from 20 smokers and 25 nonsmokers were captured using a FTS-40 IR spectrometer. Linear discriminant analysis method was used to partition the samples into smoker and nonsmoker groups according to the discriminatory patterns in the data and into a validation set to test the accuracy of the trained algorithm in distinguishing smokers and nonsmokers. Cotinine molecules were shown to exhibit a characteristic IR absorption spectrum. Several differences in the sera spectra of the two groups were observed, including an overall shift in the secondary structure of serum proteins favoring increased -sheet content in smokers. The overall accuracy of the training and validation sets was 96.7%, and 82.8%, respectively. The identification of specific absorption peaks for tobacco-induced alterations to the IR molecular profile of serum permits the development of an IR spectroscopy technique that can be used to differentiate smokers from nonsmokers. This further extends the utility of IR spectroscopy as a rapidly emerging tool in the field of molecular biodiagnostics.Abbreviations EIA Enzyme immunosorbent assay - IR Infrared - LDA Linear discriminant analysis     

Differential frontal-parietal phase synchrony during hypnosis as a function of hypnotic suggestibility

Spontaneous dissociative alterations in awareness and perception among highly suggestible individuals following a hypnotic induction may result from disruptions in the functional coordination of the frontal-parietal network. We recorded EEG and self-reported state dissociation in control and hypnosis conditions in two sessions with low and highly suggestible participants. Highly suggestible participants reliably experienced greater state dissociation and exhibited lower frontal-parietal phase synchrony in the alpha2 frequency band during hypnosis than low suggestible participants. These findings suggest that highly suggestible individuals exhibit a disruption of the frontal-parietal network that is only observable following a hypnotic induction.     

Analysis of changes in the electroencephalogram power spectrum on a new model of brain ischemia in rats

The bioelectrical activity is studied in the left and right parietal cortex by recording the power spectrum of the electroencephalogram in brain ischemia caused by complete ligation of the left common carotid artery and 50% reduction of the blood flow in the right common carotid artery in experiments carried out on nonnarcotized Wistar rats. Ischemia results in marked and stable disorders in the bioelectrical activity manifested in a decrease of the total EEG power, depression of the dominating frequency in the Θ-range, increase of the δ-range power, and interhemispheric asymmetry of some spectrogram parameters. Translated fromByulleten' Eksperimental'noi Biologii i Meditsiny Vol. 118, N ^o 12, pp. 565–567, December, 1994 Presented by E. D. Gol'dberg, Member of the Russian Academy of Medical Sciences