Electroencephalographic characteristics of cognitive-specific alerting attention in verbal learning: III. Localized characteristics of EEG spatial synchronization

Electroencephalograms (EEGs) were recorded in 19 standard derivations in 88 healthy subjects (students) in the state of rest with eyes open and during memorization (learning) of verbal bilingual semantic pairs (the Latin and Russian languages) and retrieval of information from memory (control). The estimates of EEG coherence in these states were compared for the following frequency bands: θ (4–7 Hz), α₁ (7–10 Hz), α₂ (10–13 Hz), β₁ (13–18 Hz), β₂ (18–30 Hz), and γ (30–40 Hz). Compared to the state of rest, the decrease in coherence in the pairs of derivations from the frontal and central cortical areas in all EEG frequency bands was the most pronounced for memorization, and the increase in coherence in the interhemispheric derivation pairs of the parietal-occipital region in most of the frequency bands was the most pronounced for retrieval. In addition, in the pairs formed by derivations from the parietal-occipital region with derivations from the frontal and central regions, retrieval is also characterized by an increase in coherence in the β₂ and γ bands along with its decrease in the low-frequency ranges. The dynamics of EEG coherence, when comparing the states of memorization and retrieval, is more statistically significant in the interhemispheric and cross-hemispheric pairs of derivations than in the intrahemispheric pairs. The revealed topographic specificity of the dynamics of EEG coherence owing to the change of state is considered in terms of the notion on cognitive-specific forms of sustained goal-directed mental attention.     

Multifractality of decomposed EEG during imaginary and real visual-motor tracking

We test the possible multifractal properties of dominant EEG frequency components, when a subject tracks a path on a map, either only by eyes (imaginary movement – IM) or by visual-motor tracking of discretely moving spot in regular (RM) and Brownian time-step (BM) (real tracking of moving spot). We check the hypotheses that the fractal properties of filtered EEG (1) change with respect to the law of spot movement; (2) differ among filtered EEG components and scalp sites; (3) differ among real and imaginary tracking. Sixteen right-handed subjects begin to perform IM, next – real spot tracking (RM and BM) following a moving spot on streets of a citymap displayed on a computer screen, by push forward/backward a joystick. Multichannel long-lasting EEG is band-pass filtered for theta, alpha, beta and gamma oscillations. The Wavelet-Transform-Modulus-Maxima-Method is applied to reveal multifractality [local fractal dimensions D _max(h)] among task conditions, frequency bands and sites. Non-parametric statistical estimation of the fractal measures h _{D max} is finally applied. Multifractality is established for all experimental conditions, EEG components and sites as follows among filtered components – anticorrelation (h _Dmax < 0.5) in beta and gamma, and long-range correlation (h _Dmax > 0.5) for theta and alpha oscillations; among tasks – for RM and BM, h _Dmax differ significantly whereas IM resembles mostly RM; among sites – no significant difference for local fractal properties is established. The results suggest that for both imaginary and real visual-motor tracking a line, multifractal scaling, specific for lower and higher EEG oscillations, is a very stable intrinsic one for the activity of large brain areas. The external events (task conditions) insert weak effect on the scaling.     

An autoregressive method for the measurement of synchronization of interictal and ictal EEG signals

We propose a new measure of synchronization of multichannel ictal and interictal EEG signals. The measure is based on the residual covariance matrix of a multichannel autoregressive model. A major advantage of this measure is its ability to be interpreted both in the framework of stochastic and deterministic models. A preliminary analysis of EEG data from three patients using this measure documents the expected increased synchronization during ictal periods but also reveals that increased synchrony persists for prolonged periods (up to 2 h or more) in the postictal period. Received: 20 July 1997 / Accepted in revised form: 26 January 1999     

Moderation of Increased Anxiety in Children and Teenagers with the Use of Neurotherapy: Estimation of the Efficacy

We estimated the efficacy of using the technique of feedback (FB) by EEG characteristics (EEG-FB, neurotherapy) with the aim of reducing increased anxiety levels in healthy 10- to 14-year-old children. The anxiety level was estimated using the Prikhojan anxiety test, the Spielberger–Khanin questionnaire, and the House–Tree–Person projective drawing technique. Positive effects of series of neurotherapy sessions were obvious. After training was completed, we observed significant increases in the ratios of the amplitudes of alpha and theta rhythms, semsorimotor and theta rhythms, as well as of the modal frequency of the EEG alpha rhythm in tested persons of the experimental group (n = 7). In the control group (n = 10), changes in these values did not reach the significance level. In the experimental group of tested persons subjected to EEG-FB sessions, the anxiety level decreased appreciably; in addition, the indices “feeling of inferiority” and “frustration” decreased significantly. In the control group, alterations of these psychological indices were not unidirectional. Therefore, modifications of the EEG pattern, which occurred in the course of training and were accompanied by a decrease in the anxiety level in the experimental group, can be indicative of the expediency of EEG-FB for the reduction of high anxiety levels in children and teenagers.     

Relevance of nonlinear lumped-parameter models in the analysis of depth-EEG epileptic signals

In the field of epilepsy, the analysis of stereoelectroencephalographic (SEEG, intra-cerebral recording) signals with signal processing methods can help to better identify the epileptogenic zone, the area of the brain responsible for triggering seizures, and to better understand its organization. In order to evaluate these methods and to physiologically interpret the results they provide, we developed a model able to produce EEG signals from “organized” networks of neural populations. Starting from a neurophysiologically relevant model initially proposed by Lopes Da Silva et al. [Lopes da Silva FH, Hoek A, Smith H, Zetterberg LH (1974) Kybernetic 15: 27–37] and recently re-designed by Jansen et al. [Jansen BH, Zouridakis G, Brandt ME (1993) Biol Cybern 68: 275–283] the present study demonstrates that this model can be extended to generate spontaneous EEG signals from multiple coupled neural populations. Model parameters related to excitation, inhibition and coupling are then altered to produce epileptiform EEG signals. Results show that the qualitative behavior of the model is realistic; simulated signals resemble those recorded from different brain structures for both interictal and ictal activities. Possible exploitation of simulations in signal processing is illustrated through one example; statistical couplings between both simulated signals and real SEEG signals are estimated using nonlinear regression. Results are compared and show that, through the model, real SEEG signals can be interpreted with the aid of signal processing methods. Received: 3 January 2000 / Accepted: 24 March 2000     

Correlation between the Activity of Dopaminergic Neurons of the Ventral Tegmentum and Spectral Power of the EEG Rhythms in Awake Cats

We studied correlations between the frequency of background impulse activity (BIA) of dopaminergic (DAergic) neurons of the ventral tegmentum (VT) and spectral power (SP) of the frequency components of EEG samples recorded in awake cats. The EEG was recorded monopolarly (electrodes were fixed in the cranial bones) from the frontal, occipital, and right and left temporal regions of the cortex. In a great majority of the cases, the BIA frequency of VT DA-ergic neurons demonstrated significant positive correlations with changes in the SPs of the alpha and beta EEG rhythms. The closest correlations of the spiking frequency of DA-ergic cells with the SP of the alpha rhythm was observed in the occipital region, while those with the beta SP were found in the frontal area. Correlations of the activity of DA-ergic neurons with the SPs of the alpha and beta rhythms in the left temporal cortical zone were closer, as compared with those in the symmetrical right zone. Correlations of the SPs of the delta, theta, and gamma EEG components with the discharge frequency of VT DA neurons were of opposite directions, and in most cases such correlations did not reach the level of significance. The results of this study show that, in some cases, specific EEG patterns can be considered indicators of the state of the cerebral VT DA-ergic system. Neirofiziologiya/Neurophysiology, Vol. 40, No. 4, pp. 359–367, July–August, 2008.     

Modifications of EEG Related to Directed Perception and Analysis of Olfactory Information in Humans

We recorded EEG in adult volunteers in the course of perception of smells of plant essential oils under conditions of directed attention. It was found that perception of olfactory information, even in the case of mild intensity of the smells inducing no aversive effects, correlates with noticeable changes in the EEG characteristics mostly typical of the reaction of nonspecific EEG activation induced by sensory stimulation and manifested in a decrease in the spectral power, SP, of low-frequency EEG components (6–10 Hz)). In addition, the SP of relatively high-frequency EEG components (11–25 Hz) increased; this effect was most pronounced in the occipital regions of the neocortex. Perception of the smells of essential oils was also accompanied by increases in the coherence of EEG oscillations, most intense in the β2 range (20–25 Hz). Such modifications were maximum in the left temporal/parietal region; this is interpreted as an indication of the special role of these cortical areas in the processes of interaction between the neocortical part of the olfactory analyzer and the respective structures of other analyzer systems. It is hypothesized that such interaction is necessary for the formation of a semantic image of the analyzed stimuli. Neirofiziologiya/Neurophysiology, Vol. 41, No. 1, pp. 70–78, January–February, 2009.     

Electroencephalograms of patients with initial signs of depression: Independent component analysis

Independent component analysis (ICA) of 19-channel background EEG was performed in 111 patients with the early signs of depressive disorders and in 526 healthy subjects. The power spectra of the independent components were compared in the depressive patients and in healthy subjects at the eyes closed and eyes opened states. Statistically significant differences between the groups were detected in three frequency bands: θ (4–7.5 Hz), α (7.5–14 Hz), and β (14–20 Hz). Increased θ and α activities in parietal and occipital derivations of depressive patients may have been caused by a reduced cortical activity in the projection of these derivation. Diffuse enhancement of the β activity may be correlated with anxiety symptoms that are pronounced in the clinical picture of depressive disorders at early stages of the disease. ICA used to compare quantitative EEG parameters in different groups of patients and in healthy persons makes it possible to localize the differences more accurately than the traditional analysis of EEG spectra.     

Animal model of Alzheimer’s disease: characteristics of EEG and memory

We studied the effects of aggregated amyloid β-peptide Aβ_25–35 on spatial memory and the spectral-correlational characteristics of EEG of both the dorsal hippocampus and the frontal cortex both in adult and aged rats at the early stage of Aβ_25–35 action. Spatial memory was characterized using a novel cognitive test. A decrease in low-frequency theta band oscillations in the dorsal hippocampus and the frontal cortex was observed. The mean coefficient of EEG cross-correlation between these structures was significantly reduced at the early stage of Aβ_25–35 action both in adult and aged rats. In addition, we found that one month after Aβ_25–35 injection spatial memory was impaired. These results suggest that the decrease in low-frequency theta band oscillations and the weakening of binding between the dorsal hippocampus and the frontal cortex under the action of Aβ_25–35 may be an underlying cause of the typical memory breakdown associated with the Alzheimer’s disease.     

Individual differences in brain dynamics: important implications for the calculation of event-related band power

Measures of event-related band power such as event-related desynchronization (ERD) are conventionally analyzed within fixed frequency bands, although it is known that EEG frequency varies as a function of a variety of factors. The question of how to determine these frequency bands for ERD analyses is discussed and a new method is proposed. The rationale of this new method is to adjust the frequency bands to the individual alpha frequency (IAF) for each subject and to determine the bandwidth for the alpha and theta bands as a percentage of IAF. As an example, if IAF equals 12 Hz, the widths of the alpha and theta bands are larger as compared to a subject with an IAF of, e.g., only 8 Hz. The results of an oddball paradigm show that the proposed method is superior to methods that are based on fixed frequencies and fixed bandwidths. Received: 22 July 1997 / Accepted in revised form: 22 April 1998     

Neuropsychophysiological correlates of reactive depression

To justify neurophysiological correlates of depressive disorders, the spetral parameters of EEG, peak latencies of the “late” components of auditory cognitive evoked potentials, and latencies of sensorimotor reactions in middle age and elderly patients (aged 53–72 years) during therapy of prolonged psychogenic depressive reaction (F43.21 according to ICD-10) have been studied. Initial depression severity was associated to the EEG signs of decreased functional state of the anterior areas of the left hemisphere and increased activation of the right hemisphere (especially, its temporal areas). Pronounced improvement of clinical state under the affect of psychopharmacotherapy was accompanied by acceleration of the sensorimotor reactions, a decrease in peak latencies of the “late” components (P2, N2, and P3) of auditory cognitive evoked potentials and associated with the EEG signs of improvement of functional state of the posterior areas of the brain, an enforcement of inhibitory processes in the right hemisphere (especially, in its frontal, central, and temporal areas) and more pronounced activation of frontal areas of the left hemisphere. The data are in good agreement with the concept on the systemic character of impairments of brain functioning in depression, as well as on the preferential role of the left hemisphere in control of positive emotions and the right one, of negative emotions.     

Chaotic component of human high-frequency EEG in the state of quiet wakefulness

Chaotic component of human EEG oscillations in the high-frequency band (14.7-100 Hz) was investigated. EEG was recorded from four points in symmetrical frontal and occipital scalp areas. The results of the non-linear analysis of the high-frequency EEG indicate the existence of the deterministic chaotic component with a high attractor correlation dimension. It was significantly different from the respective values of the Gaussian noise filtered in the same frequency band. In the state of quiet wakefulness (eyes closed), the dimensions of chaotic components of the EEG in all derivations did not differ from each other. Analysis of correlation pairs between the ensembles of correlation dimensions of the high-frequency EEG revealed reliable patterns of significant connections between the neocortical areas with individual features in different subjects. When the functional state of the brain was changed by hyperventilation, both the values of the correlation dimensions and the structure of inter-area connection patterns changed. We believe that the nonlinear component of high-frequency EEG is a sensitive and local characteristic of the functional state of the human brain.     

Differential effects of aging on EEG after baclofen administration

Baclofen is a selective gamma-aminobutyric acid (GABA) type B agonist that may have important medicinal uses, such as in analgesics and drug addiction treatment. In addition, evidence is accumulating that suggests GABAergic-mediated neurotransmission is altered during aging. This study investigated whether baclofen administration (5 mg kg⁻¹) induces differential effects on cortical electrical activity with age. Electroencephalograms (EEGs) were recorded from young (3–4 months) and aged (15–17 months) rats, and both the absolute and relative powers in five frequency bands (delta: 2–4 Hz; theta: 4–8 Hz; alpha: 8–12 Hz; beta: 12–20 Hz; gamma: 20–100 Hz) were analyzed. Before administration of baclofen, we found that the EEG relative power in the beta band was higher in the aged than that in the young rats. After administration of baclofen, there was a slower increase in the relative power in the delta band in the aged than that in the young rats. Moreover, there was no significant difference between the two age groups in absolute power in any frequency band. These findings indicate that baclofen treatment appears to differentially modify cortical EEG activity as a function of age. Our data further elucidate the relationship between GABA_B receptor-mediated neurotransmission and aging.     

Widespread EEG Changes Precede Focal Seizures

The process by which the brain transitions into an epileptic seizure is unknown. In this study, we investigated whether the transition to seizure is associated with changes in brain dynamics detectable in the wideband EEG, and whether differences exist across underlying pathologies. Depth electrode ictal EEG recordings from 40 consecutive patients with pharmacoresistant lesional focal epilepsy were low-pass filtered at 500 Hz and sampled at 2,000 Hz. Predefined EEG sections were selected immediately before (immediate preictal), and 30 seconds before the earliest EEG sign suggestive of seizure activity (baseline). Spectral analysis, visual inspection and discrete wavelet transform were used to detect standard (delta, theta, alpha, beta and gamma) and high-frequency bands (ripples and fast ripples). At the group level, each EEG frequency band activity increased significantly from baseline to the immediate preictal section, mostly in a progressive manner and independently of any modification in the state of vigilance. Preictal increases in each frequency band activity were widespread, being observed in the seizure-onset zone and lesional tissue, as well as in remote regions. These changes occurred in all the investigated pathologies (mesial temporal atrophy/sclerosis, local/regional cortical atrophy, and malformations of cortical development), but were more pronounced in mesial temporal atrophy/sclerosis. Our findings indicate that a brain state change with distinctive features, in the form of unidirectional changes across the entire EEG bandwidth, occurs immediately prior to seizure onset. We postulate that these changes might reflect a facilitating state of the brain which enables a susceptible region to generate seizures.     

Electroencephalographic (EEG) Measurements of Mindfulness-based Triarchic Body-pathway Relaxation Technique: A Pilot Study

Objective The “Triarchic body-pathway relaxation technique” (TBRT) is a form of ancient Chinese mindfulness-based meditation professed to give rise to positive emotions and a specific state of consciousness in which deep relaxation and internalized attention coexist. The purpose of this study was to examine the EEG pattern generated during the practice of this mindfulness exercise, and compare it to music listening which has been shown to induce positive emotions. Methods Nineteen college students (aged 19–22 years) participated in the study. Each participant listened to both the TBRT and music audiotapes while EEG was recorded. The order of presentation was counterbalanced to avoid order effect. Two EEG indicators were used: (1) alpha asymmetry index, an indicator for left-sided anterior activation, as measure of positive emotions, and (2) frontal midline theta activity, as a measure for internalized attention. Results Increased left-sided activation, a pattern associated with positive emotions, was found during both TBRT exercise and music conditions. However, only TBRT exercise was shown to exhibit greater frontal midline theta power, a pattern associated with internalized attention. Conclusions These results provided evidence to support that the TBRT gives rise to positive emotional experience, accompanied by focused internalized attention.     

Electroencephalographic characteristic of cognitive-specific alerting attention in verbal learning--III: Localized characteristics of EEG spatial synchronization

Electroencephalograms (EEG) were recorder in 19 standard derivations in 88 healthy subjects, while they were in the states: rest with eyes open; memorization (learning) of verbal bilingual semantic pairs (Latin and Russian languages); the retrieval of the rote information from memory (control). We compared estimates of EEG coherence in these states for the frequency bands theta (4-7 Hz), alpha-1 (7-10 Hz), alpha-2 (10-13 Hz), beta-1 (13-18 Hz), beta-2 (18-30 Hz), gamma (30-40 Hz). When compared with the rest most strongly expressed: for memorization a decrease of coherence in the pairs of derivations from frontal and central areas of the cortex in the EEG frequency bands; for retrieval an increase of coherence in interhemispheric derivation pairs of pariental-occipital region in majority of the frequency bands. For the retrieval also increases of coherence in the beta2 and gamma bands, along with coherence decreases at low frequencies take place in pairs formed by derivations from the parieto-occipital region with derivations from the frontal and the central ones. Dynamics of EEG coherence in comparisons of memorization and retrieval from the rest and each are expressed significantly more in the interhemispheric and crosshemispheric pairs of derivations than in the intrahemispheric pairs. Revealed topographic specificity of the dynamics of EEG coherence by changing the states is considered in terms of ideas about cognitive-specific forms of sustained goal-directed mental attention.     

Correlation between auditory sensitivity and vocalization in anabantoid fishes

Several anabantoid species produce broad-band sounds with high-pitched dominant frequencies (0.8–2.5 kHz), which contrast with generally low-frequency hearing abilities in (perciform) fishes. Utilizing a recently developed auditory brainstem response recording-technique, auditory sensitivities of the gouramis Trichopsis vittata, T. pumila, Colisa lalia, Macropodus opercularis and Trichogaster trichopterus were investigated and compared with the sound characteristics of the respective species. All five species exhibited enhanced sound-detecting abilities and perceived tone bursts up to 5 kHz, which qualifies this group as hearing specialists. All fishes possessed a high-frequency sensitivity maximum between 800 Hz and 1500 Hz. Lowest hearing thresholds were found in T. trichopterus (76 dB re 1 μPa at 800 Hz). Dominant frequencies of sounds correspond with the best hearing bandwidth in T. vittata (1–2 kHz) and C. lalia (0.8–1 kHz). In the smallest species, T. pumila, dominant frequencies of acoustic signals (1.5–2.5 kHz) do not match lowest thresholds, which were below 1.5 kHz. However, of all species studied, T. pumila had best hearing sensitivity at frequencies above 2 kHz. The association between high-pitched sounds and hearing may be caused by the suprabranchial air-breathing chamber, which, lying close to the hearing and sonic organs, enhances both sound perception and emission at its resonant frequency. Accepted: 26 November 1997     

Estimates of regional population densities of badger Meles meles, fox Vulpes vulpes and hare Lepus europaeus using walked distance sampling

Walked spotlight transect surveys with distance sampling were used to estimate regional population densities of badger (Meles meles), fox (Vulpes vulpes) and brown hare (Lepus europaeus) in south-west England (Cornwall, Devon, Gloucestershire, Herefordshire) and Wales (Pembrokeshire, Borders, North Wales). All regions were surveyed during spring 2006 with English regions re-surveyed in autumn 2006. In each region, surveys were conducted in a random sample of 19.6 km² areas (mean areas per region: spring = 19, autumn = 25). Within each survey area, a semi-random transect was established in each of a random sample of fields (open habitat almost exclusively pasture). Transects were subsequently walked at night with spotlights (mean transects per survey area: spring = 21, autumn = 21). Each area was surveyed twice during a season. Total transect length per region ranged from 137 to 193 km in spring and 230 to 250 km in autumn. The mean density of species per region was: badger 1.5–4.8 km⁻², fox 1.0–4.0 km⁻², hare 0.4–4.6 km⁻². The study has provided baseline estimates of regional densities against which any future equivalent surveys can be compared. It has also illustrated the practical application of large-scale walked distance sampling to surveys of British mammals.     

Modulation of attention in healthy children using a course of EEG-feedback sessions

We studied changes in the power spectra of EEG in the course of sessions of feedback by EEG characteristics (neurofeedback sessions) and estimated the effects of neurofeedback on psychological and EEG correlates of voluntary attention. Indices of the latter were estimated using Bourdon’s test (a correcture test) and Schulte’s tables. Twenty-nine reasonably healthy 10-to 13-year-old children took part in the study; they were divided into two groups, an experimental group (n = 12) and a control group (n = 15). The results obtained support the statement on noticeable changes in the functional state of the brain both immediately in the course of a neurofeedback session and after a course of such trainings. Changes in the ratios of the spectral powers of the beta₁ vs theta rhythms and the low-frequency beta vs theta rhythms were found in EEG recorded from the sensorimotor zone of the right hemisphere (C4). The observed changes in the spectral characteristics of EEG induced by the course of neurofeedback sessions were accompanied by the improvement of a few indices of voluntary attention. Neirofiziologiya/Neurophysiology, Vol. 38, Nos. 5/6, pp. 458–465, September–December, 2006.     

Elevated S100B and Neuron Specific Enolase Levels in Patients with Migraine-without Aura: Evidence for Neurodegeneration?

Although migraine has mainly been considered as a benign disease, there is cumulative evidence of silent changes in the brain, brainstem, or cerebellum and subtle subclinical cerebellar dysfunction. In this study, in order to investigate a possible neuronal and/or glial damage at the cellular level in migraine, we measured and compared serum levels of S100B which is a protein marker of glial damage or activation, and neuron specific enolase (NSE) which is a marker of neuronal damage, in migraine patients and control subjects. Serum levels of S100B and NSE were measured in blood samples from 41 patients with migraine-without aura taken during a migraine attack (ictal) and in the attack-free period between migraine attacks (interictal) and 35 age- and sex-matched controls. Patients with migraine-without aura had significantly higher ictal serum levels of S100B and NSE (P < 0.05, for both) than control subjects; whereas in the interictal phase, there was a significant increment only in S100B levels (P < 0.05) compared to controls. On the other hand, serum levels of S100B and NSE in ictal and interictal blood samples did not differ significantly. The findings of increased ictal serum S100B and NSE levels together with increased interictal levels of S100B suggested that migraine might be associated with glial and/or neuronal damage in the brain and a prolonged disruption of blood–brain barrier. Increased interictal serum levels of S100B might point out to an insidious and slow damaging process in migraine patients.