Spatial organization of EEG activity during active hyperventilation (cyclic breath) I. general patterns of changes in brain functional state and the effect of paroxysmal activity

Changes in spatial organization of EEG activity were analyzed in 44 humans during active 1-h hyperventilation using cyclic or circular breath (CB) technique similar to rebirthing breath technique. The dynamics of different indices was recorded each 5 min (using 12 time slots). A double-humped pattern of changes in spatial organization indices (linear processes) and spatial disorder (nonlinear processes) of biopotentials: an initial decrease within 1 to 20–30 min and a second one from 35–40 min to the end of session. A complex dynamics of spatial frequency processes (coherence and spectral power of biopotentials) with different pattern of changes within narrow frequency EEG bands. The dynamics of the spatial organization of EEG indices proved to depend on the intensity of hyperventilation-induced paroxysmal activity. The indices of spatial synchronization and disorder of biopotentials as well as low frequency β-activity (16.00–22.50 Hz) decreased more at the background of high rather than low paroxysmal activity, while the low frequency components (Δ and Θ) and high frequency α-activity (11.25–12.50 Hz) increased more. The obtained data are considered in terms of specific consciousness state induced by CB.     

Dynamics of spatial synchronization of EEG parameters during relaxation and their relationship with regulation of heart rate

EEG parameters were analyzed in a wide frequency range for the estimation of the possible functional importance of different EEG components in the formation of relaxation. Sixty-five subjects aged 17–20 years were involved in the investigation. The relaxation session with monopolar EEG recording and autonomic parameters recording was carried out for each subject. During the relaxation significant changes were observed in all analyzed EEG ranges. Two types of changes of EEG coherence in the wakefulness-relaxation shift of state were distinguished, and correlation of the type of dynamics with the LF/HF ratio, showing the balance of sympathetic and parasympathetic parts of the autonomic nervous system, was found.     

Quantitative assessment of maps of the cortical background potentials during the adaptation of freely moving animals to environmental situations

Utilization of spectral-correlation methods of EEG analysis, due to necessary averaging in time, does not make it possible to detect dynamic phenomena in spatial-temporal organization of brain potentials. Non-traditional method is presented of quantitative evaluation of the changes of spatial-temporal correlation of cortical potentials--comparison of successive momentary potentials relief (electroencephalotopograms--EETG). Joint utilization of dynamics of similarity coefficients of successive EETG (Ket), mean values of EETG (Yet) and some other parameters allows to judge about dynamic properties of spatial correlations of potentials of freely moving animals in adaptation process to the environment during which alternation is established of the active and passive phases in decaminute intervals. Quantitative evaluation of spatial-temporal organization of the parameters of rabbits cortical potentials in these phases and in transition periods has revealed their informative possibilities.     

The activity of hippocampal neurons during several types of behavior]

The activity of 87 hippocampal units and the EEG (field CAI) were studied in unrestrained rabbits during calm and active alertness and at different stages of sleep. Correlation has been established between the characteristics (mean frequency and the pattern) of unit firing, EEG and the animal's activity. For most of the neurones, fixed values of mean frequency and the discharge pattern corresponded to a definite functional state. With transition from sleep to alertness, 63.6% of the units became active, 29.1% were inhibited, and the rest of the units changed the firing pattern only. The cells which became activated during awakening, showed a reduced firing frequency during a more profound sleep and higher discharge frequency during the paradoxal phase of sleep, while the inhibitory cells revealed reverse dynamics of discharge frequency. In a state of alertness, the most pronounced shifts in firing activity were observed in 33.3% of the nerve cells at orienting investigating behaviour, in 27.1%, during attention reaction, in 22.9% at some kinds of movement, and in 16.7%, in the course of feeding and drinking. A conclusion has been drawn that the role of the hippocampus in achieving different behavioral reactions is probably to a great extent determined by its participation in setting up a level of the brain central tone, specific for each state.     

The research of constructing dynamic cognition model based on brain network

Estimating the functional interactions and connections between brain regions to corresponding process in cognitive, behavioral and psychiatric domains is a central pursuit for understanding the human connectome. Few studies have examined the effects of dynamic evolution on cognitive processing and brain activation using brain network model in scalp electroencephalography (EEG) data. Aim of this study was to investigate the brain functional connectivity and construct dynamic programing model from EEG data and to evaluate a possible correlation between topological characteristics of the brain connectivity and cognitive evolution processing. Here, functional connectivity between brain regions is defined as the statistical dependence between EEG signals in different brain areas and is typically determined by calculating the relationship between regional time series using wavelet coherence. We present an accelerated dynamic programing algorithm to construct dynamic cognitive model that we found that spatially distributed regions coherence connection difference, the topologic characteristics with which they can transfer information, producing temporary network states. Our findings suggest that brain dynamics give rise to variations in complex network properties over time after variation audio stimulation, dynamic programing model gives the dynamic evolution processing at different time and frequency. In this paper, by applying a new construct approach to understand whole brain network dynamics, firstly, brain network is constructed by wavelet coherence, secondly, different time active brain regions are selected by network topological characteristics and minimum spanning tree. Finally, dynamic evolution model is constructed to understand cognitive process by dynamic programing algorithm, this model is applied to the auditory experiment, results showed that, quantitatively, more correlation was observed after variation audio stimulation, the EEG function connection dynamic evolution model on cognitive processing is feasible with wavelet coherence EEG recording.     

Dynamics of the Adolescent EEG Parameters with Changes in the CNS Functional State (Relaxation) Influenced by Rhythmic Acoustic Stimulation

Age-related specific features of the regulation of the CNS functional state (relaxation) were studied in adolescents between the ages of 14 and 15 years using 6-Hz rhythmic stimulation. The dynamics of the EEG findings (spectral power density, coherence functions) in the quiet wakefulness–relaxation–initial-state cycle was analyzed. The dynamics of the functional state was controlled by changes in the electrodermal resistance (EDR). The data showed that the studied group of adolescents was heterogeneous by the effectiveness of self-regulation: the majority was characterized by marked shifts whose distribution character was close to normal; the others, by mild EDR changes. It was shown that, with the use of rhythmic stimulation, relaxation shifts were more marked than those induced by common psychotherapeutic techniques. The basic relaxation changes in the EEG parameters are related to changes in the coherence function values, i.e., increases in its values, especially those of distant relations (with the focus) of significant connections in the frontal regions. The rate of the occurrence of relaxation changes in the coherence values is substantially higher in the low-frequency band (5 to 7 Hz) than in the EEG -band, constituting 20 to 50% in terms of different relations. The revealed specific features of the relaxation dynamics of the EEG parameters are analyzed in the age-related aspect. The influence of higher structures of the CNS and puberty-related rearrangements in the system of neuroendocrine regulation on the effectiveness of the regulatory function is discussed.     

Dynamics of EEG-indicators in alcohol abstinence

To study the possibility of discrimination of different periods of alcohol abstinence state (acute, subacute, and arrested) the brain electrical activity of 30 patients with chronic alcoholism was recorded from 24 sites of convexital scalp surface during the detoxication. The "Synchro-EEG" program package was applied for EEG processing using 840 parameters. Sets of state-specific characters were selected, and an integral parameter for estimation of the brain functional state was developed. Parameters of coherence of biopotentials in narrow frequency subbands turned to be of the greatest informative value. As compared to the normal state, in the acute period all the frequency components were changed. Their dynamics during detoxication was different. Delta and theta activity were normalized faster then the alpha and beta frequencies. The dynamics of the spatial synchronization foci reflected the recovery of consciousness and normalization of the brain functional state.     

A neurophysiological analysis of the forms of wakefulness and rest in the toad Bufo bufo and the frog Rana ridibunda in the circadian cycle

Studies have been made on the spectral EEG parameters in the forebrain and midbrain of the toad and frog during active and passive forms of natural behaviour within a diurnal cycle. Basing on evaluation of animal reactivity and on EEG analysis performed by presentation of the power of EEG signals via the frequency spectrum, it is possible to obtain a reliable identification of functional condition of amphibians. Behavioural and EEG patterns of 3 forms of wakefulness and 2 forms of rest are presented for frogs and toads.     

A Pharmacokinetics-Neural Mass Model (PK-NMM) for the Simulation of EEG Activity during Propofol Anesthesia

Modeling the effects of anesthetic drugs on brain activity is very helpful in understanding anesthesia mechanisms. The aim of this study was to set up a combined model to relate actual drug levels to EEG dynamics and behavioral states during propofol-induced anesthesia. We proposed a new combined theoretical model based on a pharmacokinetics (PK) model and a neural mass model (NMM), which we termed PK-NMM—with the aim of simulating electroencephalogram (EEG) activity during propofol-induced general anesthesia. The PK model was used to derive propofol effect-site drug concentrations (C _eff) based on the actual drug infusion regimen. The NMM model took C _eff as the control parameter to produce simulated EEG-like (sEEG) data. For comparison, we used real prefrontal EEG (rEEG) data of nine volunteers undergoing propofol anesthesia from a previous experiment. To see how well the sEEG could describe the dynamic changes of neural activity during anesthesia, the rEEG data and the sEEG data were compared with respect to: power-frequency plots; nonlinear exponent (permutation entropy (PE)); and bispectral SynchFastSlow (SFS) parameters. We found that the PK-NMM model was able to reproduce anesthesia EEG-like signals based on the estimated drug concentration and patients’ condition. The frequency spectrum indicated that the frequency power peak of the sEEG moved towards the low frequency band as anesthesia deepened. Different anesthetic states could be differentiated by the PE index. The correlation coefficient of PE was 0.80±0.13 (mean±standard deviation) between rEEG and sEEG for all subjects. Additionally, SFS could track the depth of anesthesia and the SFS of rEEG and sEEG were highly correlated with a correlation coefficient of 0.77±0.13. The PK-NMM model could simulate EEG activity and might be a useful tool for understanding the action of propofol on brain activity.     

The effect of BFB training on the efficiency of voluntary relaxation in junior schoolchildren

Psychophysiological features of schoolchildren seven to eight and nine to ten years of age (their autonomic balance and brain functional state) were studied; the effect of biofeedback (BFB) training on the regulatory influence of relaxation was evaluated (BFB signal—electrical skin resistance). Before and after BFB training, the electrophysiological experiment, i.e., relaxation testing, was performed without BFB in three situations: background, relaxation, and the state after relaxation. The EEG of various cortical areas was recorded, and the electrical skin resistance was determined. The short-term memory test was used to determine changes in the functional state at the behavioral level. Short-term training (five sessions) often enhanced the efficiency of voluntary relaxation and improved the postrelaxation mnestic function only in the group of 9- to 10-year-old children. The effect of training on the relaxation of the regulation depended on the individual psychophysiological features of children.     

Effect of Individual Features of the CNS on Efficiency of Relaxation Biofeedback Training in 9- to 10-Year-Old Children

The possibilities of biofeedback training for improvement of the self-control of the functional state (relaxation) were studied in 9- to 10–year-old children. At the first stage, under conditions of electrophysiological experiment, relaxation shifts were assessed in the cycle quiet wakefulness–relaxation–recovery of the initial state by autonomic (skin resistance) and EEG (spectra and coherence) indices. The children were then trained to control their functional state with a computer game including a feedback loop by skin temperature. After the training cycle, children were repeatedly examined in electrophysiological experiment with the instruction to control their state. Comparative analysis of self-induced relaxation changes before and after a successful training course revealed greater shifts of skin resistance and an increase in the number of distant functional connections (especially, in the intermediate and high-frequency EEG subbands), with a significantly increased coherence level during relaxation. A correlation was found between the efficiency of self-regulation training and some individual psychophysiological characteristics (simple motor reaction time, autonomic coefficient, resting EEG). Low efficiency of self-control training was observed in younger schoolchildren with a sharply deviant (from the mean group values) reaction time and autonomic coefficient, as well as with EEG manifestations of functional immaturity of the upper brain regulatory structures. The dependence of the EEG changes on the self-regulation strategy is discussed on the basis of obtained evidence and data in the literature.     

Brain oscillatory activity during sleep shows unknown dysfunctions in early encephalopathy

Electroencephalographic recordings in cirrhotic patients without overt hepatic encephalopathy (HE) have mainly been performed during wakefulness. Our aim was to quantify their alterations in nocturnal sleep electroencephalogram (EEG). In 20 patients and 20 healthy volunteers, we recorded a nocturnal digital polysomnography. Different sleep parameters were measured. Besides, we performed quantitative analysis of EEG (qEEG) as follows: spectral power in the different sleep stages was calculated in the frequency bands low δ, δ, θ, α, and σ. Also, the mean dominant frequency and Sleep Indexes were obtained. In comparison with controls, the group of patients showed (1) different alterations in both the microstructure and the macrostructure of sleep; (2) an increase in, both, θ band power and the average mean dominant frequency during rapid eye movement (REM); (3) in all sleep stages, a decrease of sleep electroencephalogram spectral power in low δ band and an increase in δ band: and (4) in stages N3 and REM, significant increases in the minimum of mean dominant frequency and in the respective sleep indexes. Therefore, in cirrhotic patients without overt HE, and likely having minimal hepatic encephalopathy, we found different alterations in both the microstructure and the macrostructure of nocturnal sleep. Also, sleep qEEG showed a brain dysfunction in slow oscillatory mechanisms intrinsic of sleep stages, with an increase in the frequency of its maximal electroencephalogram synchronization, from low δ to δ band. These alterations may reflect the onset of encephalopathy; sleep qEEG may, thus, be an adequate tool for its brain functional evaluation and follow-up.     

Influence of Short-Term Relaxation on the Organization of the Brain Electrical Activity of Young Schoolchildren in the State of Quiet Wakefulness

Relaxation-induced changes in characteristics of the functional state of the nervous system (EEG parameters and electrodermal resistance (EDR)) were studied in 30 schoolchildren aged 9–10 years. A multichannel EEG was recorded from the occipital, parietal, temporo-parieto-occipital, central, and frontal areas of both brain hemispheres in three test conditions: quiet wakefulness, R, and recovery of the initial state. Simultaneously, the EDR was monitored. EEG amplitude spectra and coherence were calculated. Prior to and after relaxation, a cognitive test to determine the extent of short-term auditory verbal memory was performed. While changes in the EDR were reversible, relaxation-induced changes in the EEG parameters persisted after relaxation in many subjects. Changes in EEG coherence between distant derivations were most stable. Since short-term auditory verbal memory improved after relaxation, the postrelaxation changes in the EEG parameters were considered to reflect positive changes arising in the brain function and increasing the efficiency of cognitive processes.     

Alpha-bursts and K-complex: phasic activation pattern during spontaneous recovery of correct psychomotor performance at difference stages of drowsiness

It is known that phasic activation processes reveal themselves by different electrophysiological patterns depending on the sleep depth. Alpha bursts are an electrophysiological manifestation of arousal at the initial stage of sleep, whereas at the II stage K-complex becomes the main arousal pattern. We have shown earlier that during light drowsiness spontaneous recovery of correct psychomotor test performance (after an error) by a sitting subject is accompanied by EEG alpha bursts. The aim of this work was to study the EEG phasic activation pattern at deeper drowsiness during test performance by a subject in a lying position. Subjects had to press sensitive button in a lying position with closed eyes with self-paced oral counting of pressings. The experiment lasted for 40 min; EEG, EOG, and button pressing were recorded. It was shown that recovery of correct performance after errors at deeper drowsiness was accompanied by two types of EEG phasic activation patterns (PAP-1 and PAP-2). The alpha frequency component was always present in both PAP-1 and PAP-2. PAP-1 were observed at early stages of drowsiness and consisted of high-amplitude alpha bursts and EEG activity of higher frequency. PAP-2 were recorded at deeper stages and consisted of K-complexes with superposition of PAP-1. At first (medium level of drowsiness) the alpha bursts were superposed on the late slow K-complex components. With further deepening of drowsiness the early fast components of K-complex were also observed. The early appearance of K-complex during test performance at drowsiness seems to be associated with the urgent run of brain arousal systems, which at spontaneous falling asleep are in operation at the II sleep stage.     

Electroencephalographic markers of the spontaneous recovery of the vertical posture in patients with consequences of traumatic brain injury

Nine patients (mean age, 23.6 ± 3.15 years) with a severe traumatic brain injury (TBI) associated with a loss of the ability to maintain vertical posture were enrolled in a comprehensive clinical and electroencephalographic study during the spontaneous recovery of vertical posture (VP). The patients were divided into three groups according to their functional deficit assessed on the international MPAI, FIM, and MMSE scales, which was determined by the severity of the TBI. The EEG data were compared to those of ten healthy subjects (mean age, 22.8 ± 0.67 years). In patients with a moderate impairment of the brain and a rapid recovery of VP (over two weeks), a change in the sitting position revealed EEG signs similar to reactive EEG restructurings of healthy individuals during the maintenance of VP in the form of a predominant EEG coherence increase in the right hemisphere for most of the rhythm bands; however, at this stage of VP recovery, the EEG restructurings retained pathological signs. In patients with a more severe functional deficit, spontaneous recovery of VP was accompanied by hyperreactive EEG restructurings for all rhythm bands without regional specificity. This finding showed up irrespective of the lateralization of the brain injury, which could be considered as a marker of positive dynamics of VP recovery. In patients with the most severe impairment and functional deficit and long-term (more than three months) absence of spontaneous VP recovery, the absence of reactive EEG restructurings was revealed in their passive verticalization, which could be used as a marker of negative prognosis.     

Assessing Movement Factors in Upper Limb Kinematics Decoding from EEG Signals

The past decades have seen the rapid development of upper limb kinematics decoding techniques by performing intracortical recordings of brain signals. However, the use of non-invasive approaches to perform similar decoding procedures is still in its early stages. Recent studies show that there is a correlation between electroencephalographic (EEG) signals and hand-reaching kinematic parameters. From these studies, it could be concluded that the accuracy of upper limb kinematics decoding depends, at least partially, on the characteristics of the performed movement. In this paper, we have studied upper limb movements with different speeds and trajectories in a controlled environment to analyze the influence of movement variability in the decoding performance. To that end, low frequency components of the EEG signals have been decoded with linear models to obtain the position of the volunteer’s hand during performed trajectories grasping the end effector of a planar manipulandum. The results confirm that it is possible to obtain kinematic information from low frequency EEG signals and show that decoding performance is significantly influenced by movement variability and tracking accuracy as continuous and slower movements improve the accuracy of the decoder. This is a key factor that should be taken into account in future experimental designs.     

Brain rhythms reveal a hierarchical network organization

Recordings of ongoing neural activity with EEG and MEG exhibit oscillations of specific frequencies over a non-oscillatory background. The oscillations appear in the power spectrum as a collection of frequency bands that are evenly spaced on a logarithmic scale, thereby preventing mutual entrainment and cross-talk. Over the last few years, experimental, computational and theoretical studies have made substantial progress on our understanding of the biophysical mechanisms underlying the generation of network oscillations and their interactions, with emphasis on the role of neuronal synchronization. In this paper we ask a very different question. Rather than investigating how brain rhythms emerge, or whether they are necessary for neural function, we focus on what they tell us about functional brain connectivity. We hypothesized that if we were able to construct abstract networks, or "virtual brains", whose dynamics were similar to EEG/MEG recordings, those networks would share structural features among themselves, and also with real brains. Applying mathematical techniques for inverse problems, we have reverse-engineered network architectures that generate characteristic dynamics of actual brains, including spindles and sharp waves, which appear in the power spectrum as frequency bands superimposed on a non-oscillatory background dominated by low frequencies. We show that all reconstructed networks display similar topological features (e.g. structural motifs) and dynamics. We have also reverse-engineered putative diseased brains (epileptic and schizophrenic), in which the oscillatory activity is altered in different ways, as reported in clinical studies. These reconstructed networks show consistent alterations of functional connectivity and dynamics. In particular, we show that the complexity of the network, quantified as proposed by Tononi, Sporns and Edelman, is a good indicator of brain fitness, since virtual brains modeling diseased states display lower complexity than virtual brains modeling normal neural function. We finally discuss the implications of our results for the neurobiology of health and disease.     

Some Neurophysiological Correlates of Altered Mental States in Labor: Report II. Features of the Superslow Phasic Processes

A group of parturient women (n= 45) was divided into subgroups of subjects with a large and small number of signs of an altered mental state (AMS and NAMS, respectively) during and after labor, according to data of a special psychological questionnaire. The background EEG and the superslow phasic electric processes (SSPP) of the head surface were recorded simultaneously in 16 monopolar leads before and after labor. The parameters of autocorrelation and cross-correlation functions of the processes were calculated. Highly significant differences were found among the subgroups in the parameters of dynamics and spatial synchronization of the SSPP, related, in particular, to the activity of the anterofrontal zones of both hemispheres and of the temporal zones of the right hemisphere. The differences between the AMS and NAMS subgroups were revealed on the basis of the different extents of the unidirectional deviations from the SSPP parameters in the reference group of healthy nulliparous women. The pattern of interrelations of the investigated parameters of the EEG and the SSPP confirms the hypothesis that functional changes in the brain during the adaptation of women to pregnancy termination and physiological labor correlate with a special mental state.     

Changes in EEG and higher nervous activity of rats during cerebral anti-ischemic protection by acelysin]

The water-soluble aspirin (acelysin) has been used as an anti-ischaemic protector when injected in the dose of 150 mg/kg 30 min before ischaemia. The EEG has been registered during the whole period of experiment and the total EEG power index has been calculated. The higher nervous activity has been evaluated during analysis of rat's abilities for elaboration of conditional reflex of an active escape reaction in Y-labyrinth. The results have demonstrated the complete rehabilitation and restoration of brain functional activity 8 days after endurance of brain ischaemia under protection of acelisin.     

Effect of high dose cytosine arabinoside on quantitative EEG in patients with acute myeloid leukemia

Background EEG activity is considered an index of functional state of brain. Chemotherapy (CT), used for non-central nervous system (CNS) cancer, can cross the blood brain barrier and contribute to changes in the functional state of brain that can alter background EEG activity. Quantitative EEG (qEEG) is superior to conventional EEG in the detection of subtle alterations of EEG background activity and for this reason, the use of qEEG might assist the clinician in evaluating the possible effect of CT on the CNS. The nucleoside analog cytosine arabinoside (Ara-C) is one of the milestone chemotherapeutic agents used for treatment of acute myeloid leukemia (AML). Our observational study evaluates the possible effect of Ara-C on the qEEG of patients with AML, without CNS involvement. We conducted an observational study on newly diagnosed AML patients without CNS involvement, undergoing treatment with Ara-C to analyze the possible effect of Ara-C high doses on EEG background activity using qEEG analyses. A total of nine AML patients, 5 with Ara-C i.v. high dose (≥3 g/m² die), 4 with standard dose (100 mg/m² die) underwent qEEG (at rest, during hyperpnoea, mental arithmetic task and blocking reaction). We compared the EEG background activity of the two groups at baseline and after 6 months. Statistical analysis showed no significant differences between the two groups in mean relative power for all frequency bands, at rest and during hyperpnoea, mental arithmetic task and blocking reaction. Our data indicate that high dose Ara-C i.v. did not induce significant changes on EEG background activity in our patients. Future research in this area could include prospective studies that would combine qEEG and neuropsychological testing to assess the impact of CT on brain functions.