Psychophysiologic parameters of reproducing emotions in healthy subjects and patients during the first episode of depression

We analyzed the spectral power of EEG rhythms and some psychological features in patients with depression (first episode) and in healthy subjects. In the control group, the distributions of the spectral power of the alpha3 and gamma rhythms was symmetrical. In reproducing joy, the power of the alpha3 rhythm increased in the occipital and that of the gamma rhythm increased in the temporal areas of the left hemisphere. In depressive patients, predominant activation of the left posterior cortical quadrant in the alpha3 band was observed both in the baseline activity and during reproducing emotions of both valences. In these patients, the gamma rhythm predominated in the anterior regions of the right hemisphere during rest. The mental reproduction of joy and grief in depressive patients shifted the maximal gamma rhythm spectral power to the occipital cortical regions. Thus, in depressive patients, any emotional load, regardless of its valence, results in a decrease in the pathologic gamma activity and makes the distribution of cortical electric activity more close to that of healthy subjects.     

Correspondence between spectral power and synchronization of the brain rhythms in the norm and cognitive pathology

The work is aimed at the study of correlations between the measures of spectral power and cortical interactions of EEG rhythms in healthy subjects and schizophrenic patients ("acute" and chronic cases). All brain rhythms in healthy subjects appeared to be symmetrical and synchronous both in phase and frequency. In "acute" schizophrenics, opposite to healthy subjects, the distribution of cortical activity is asymmetrical, and in the chronic cases, the spectral power of most cortical rhythms is decreased as compared to healthy subjects. In the "acute" patients, interhemispheric connections are absent in all rhythms but alpha. In the chronic patients, the number of cortical connections is slightly higher than in the acute patients; and they are located in the posterior areas in the gamma rhythm. These neurophysiological aberrations evidently underlie the multiple mental activity disorders in schizophrenic patients. Thus, the correspondence between the brain rhythms and their synchronization is a necessary condition for normal perception, emotions and cognition evidently influencing behavior and consciousness.     

Impairment of space-frequency parameters of EEG coherence during cognitive performance (consequences of Chernobyl accident)

Changes in frequency and space parameters of the EEG coherence evoked by cognitive performance were analyzed in 13 healthy subjects and participants of the Chemobyl clean-up. In healthy subjects, the EEG coherences in the alpha and beta frequency bands were significantly increased during arithmetic count and during visuospatial performance. Each test was characterized by regionally-specific features. Chemobyl patients demonstrated a global decrease in the EEG coherence predominantly in the alpha and beta frequency bands, especially in the frontal cortical areas. Patients with various pathological EEG patterns demonstrated specific impairment of EEG parameters. In patients with a "flat" EEG pattern, the EEG coherence predominantly decreased in the frontal associative areas, especially during arithmetic calculation. In patients with a "hypersynchronous" EEG pattern, the decrease in the EEG coherence was most pronounced in the parietal associative areas, especially during the visuospatial performance. The revealed impairments of the EEG coherence reactivity may be a reflection of disorders of the intracortical and corticosubcortical interaction and can result from the remote postradiation brain atrophy, especially, of cortical structures.     

Features of the spectral power of the EEG rhythms in autistic children and their relation with the progress of different symptoms in schizophrenia

Right hemispheric dominance of the baseline alpha-band spectral power was revealed in 5-7 years boys with autism. This feature persisted during performance of a cognitive task (counting). Also, boys with autism showed lowered level of the alpha spectral power as compared with healthy children. In healthy children, the gamma spectral power increased during performance of the cognitive task as compared to baseline state. Autistic persons showed higher values of the gamma spectral power as compared with normal boys. Boys with autism showed less expressed changes in the gamma spectral power during the cognitive task than healthy children. The reduced spectral power of the alpha band in autistic boys may serve as a precursor of conversion from autism to schizophrenia. Higher level of the gamma spectral power in autistic boys is characteristic also of schizophrenic patients with positive symptoms. Lowered levels of fast rhythms reactivity revealed in autistic boys and the same effect earlier described in schizophrenic adults probably have the similar nature.     

Spectral power and cortical interactions in the beta2 rhythm in normal subjects and schizophrenic patients

Spectral and coherence characteristics of the beta 2 rhythm (20-40 Hz) were compared in patients with acute schizophrenia (the first episode), patients with chronic schizophrenia (disease duration more than two years), and healthy subjects (control group) during cognitive task performance. Examination showed the "excessive" spectral power of this rhythm in the prefrontal cortical areas in patients with acute schizophrenia and its "insufficient" spectral power in all derivations of the right hemisphere in patients with the chronic form as compared to the controls. The similarity of the beta 2 spectral power distribution in different cortical areas measured by covariance method decreased with increase in psychopathologic manifestations. Coherent analysis revealed a substantially lower number of cortico-cortical functional connections in schizophrenic patients than in healthy subjects, absence of interhemispheric connections in patients with acute schizophrenia, and a slight increase in their number if patients with the chronic disease. However, as distinct from the controls revealing many inter- and intrahemispheric connections in all cortical areas, in schizophrenics the interhemispheric connections were observed only in the posterior cortical regions. The results point to a disorder of interhemispheric interaction in schizophrenia.     

Spectral characteristics of EEG during formation a set to illusory length perception (Müller-Lyer illusion)

A cognitive set to illusory perception of linear relationships was formed in 56 young healthy subjects. After 10 presentations of Müller-Lyer figures, 39 subjects formed the stable set. In 17 subjects the unstable set was formed. The spectral power of the EEG led from different cortical areas was studied at different stages of set formation. Analysis of variance showed that the factors "set stage" and "group" x "set stage" x "hemisphere" exert significant influence on the EEG spectral power in the delta range in the frontal area. In the subjects with stable set, the power of this spectral component increased at the stages of set formation and actualization and returned to its initial values during set extinction. The between-group difference was more expressed in the left hemisphere. In subjects, which formed the stable set, the power of the occipitotemporal alpha rhythm in the reference state was higher than in subjects with the unstable set. In the process of set formation, the dynamics of the alpha spectral component (8-10 Hz) was more expressed in the stable group: its power increased to a greater extent at the stages of set actualization and extinction. In both groups, there were no significant changes in the alpha2 power over the course of the experiment.     

Comparative EEG study in normal and autistic children

The work represents the results of a comparative study of spectral power as well as averaged coherence in alpha, beta and gamma EEG bands in 5-to-7-year-old autistic and healthy boys in the state of rest and under cognitive load (mental calculation). The mean age of the examined children was 6 years 4 months. In both healthy and autistic children, there was a clear-cut baseline frontal-occipital gradient of the alpha activity. Performance of the cognitive task led to enhancement of spectral power in the alpha1 band and shifting its maximum to the left hemisphere, did not change the activity in the alpha2 band, and considerably increased the spectral power in the alpha3 band. In healthy children, the spectral power and average coherence of the fast rhythms increased in the central and frontal areas of the left hemisphere. The right-side dominance of the spectral power of the alpha band was revealed in autistic children both in the baseline and during cognitive task. The spectral power of the gamma band was higher in autistic children than in healthy children in the baseline. The cognitive task did not change this fast activity in autistic children.     

Context-dependent EEG spectral characteristics during performance of tasks

Spatial and frequency EEG characteristics of two groups of healthy adult subjects were examined in two series of experiments, which differed in conditions of the second cognitive task in a trial. The first task was the same in the two series: subjects had to evaluate size relationship between two closely spaced circles. The second task successively presented in trials of the first series consisted in the recognition of words/pseudowords, and in the second series, subjects had to localize a target letter in a matrix. It was assumed that the cognitive performance in the first series predominantly involved the ventral visual system, whereas during task performance in the second series, predominant involvement of the ventral and dorsal visual systems alternated. Multichannel EEG fragments recorded prior to the presentation of the task pairs were analyzed. Analysis of variance of the EEG spectral power revealed the generalized significant effect of the factor of the second task in the pair for delta band and lower beta subband, the power being higher in the first series. Factor brain hemisphere had a significant effect for the alpha band in the occipital area, the spectral power being lower in the left hemisphere for both experimental series. The task x hemisphere interaction was significant in the temporal cortical areas for the EEG power in alpha2 band, i.e., the predominant involvement of the ventral visual system was associated with stronger asymmetry of alpha2 rhythm and lower spectral power in this band in the left temporal area. Thus, the character of the forthcoming cognitive activity was shown to be reflected in spatio-frequency characteristics of the preceding EEG.     

Analysis of EEG characteristic at early stages of depression using method of independent components

Independent Component Analysis (ICA) was used for 19-channel resting EEG analysis 111 patients at early stages of depressive disorder and 526 age-matched healthy subjects. Comparison of independent components power spectra in depressed patients and healthy subjects in two states: Eyes closed and Eyes open, has revealed significant differences between groups for three frequency bands: Theta (4-7.5 Hz), Alpha (7.5-14 Hz), and Beta (14-20 Hz). Increased power of alpha and theta activity in depressed patients at parietal and occipital sites may be caused by decreased cortical activation of these regions. Diffuse enhancement of beta activity level can correlate with anxiety symptoms which take an important place in clinical picture of depressive disorder at early stages. Using of ICA method for comparison of spectral characteristics of EEG in groups of patients with different brain pathology and healthy subjects gives a possibility to localize more precisely the discovered differences as compare to traditional analysis of EEG spectra.     

Cortical connectivity in schizophrenic patients with positive and negative symptoms

The paper is dedicated to the problem of disturbed "connectivity" between different cortical areas in schizophrenic patients with the dominance of "negative" and "positive" symptoms. The architecture of cortical connections in high-frequency range of the beta rhythm (beta 2, 20-40 Hz) was studied in three groups of right-handed men: healthy control group (16 subjects) and schizophrenic patients with the dominance of positive (16 subjects) and negative (22 subjects) symptoms assessed by the SAPS and SANS scales. Two versions of the Intracortical Interaction Mapping (IIM) technique of examination of cortical connections were used. In the 1st version, mean connection frequencies in the beta 2-rhythm for each group were analyzed. In the 2nd version, the most typical for a given group connection frequencies were studied. Additionally, since the IIM technique is rather new, coherence function in the beta 2-rhythm calculated by the standard way was also taken into account. The obtained results made it possible to reveal the derangements in the system of cortical interactions in schizophrenic patients.     

Background activity of the brain in healthy mental aging

The EEG mapping study tested age-related changes in power of EEG rhythms from delta to gamma ranges under healthy cognitive aging associated with preserved cognitive abilities and involvement in complex professional activity. 32 subjects of higher age group (HAG, mean age 65.1 +/- 1.18, 14 men and 18 women) and 33 subjects of lower age group (LAG mean age 22.1 +/- 0.38, 18 men and 15 women) participated in the study. Mean power of slow (delta, theta and alpha2) activity decreased and of fast activity (beta, gamma) increased as subject age increased. Compared to subjects of LAG subjects of HAG displayed a reduction in heterogeneity of EEG activity across recording sites. Centro-temporal gradients of power for frequency ranges from delta to beta2 and frontoparietal gradients and hemispheric asymmetry for alpha and beta1 rhythms were smoothed in subjects of HAG. These results suggest that observed age-related changes in baseline EEG may be the prerequisite for compensatory neural recruitment that may be associated as with allocation of more resources in cognitive processes so with reorganization of cortical networks including areas susceptible to physiological changes with aging.     

EEG correlates of individual differences in performance efficiency of students during examination stress

Performance of cognitive tests and EEG spectral power were evaluated in 39 students aged from 19-21 years in two conditions: during common educational process and immediately before examination (stress condition). Before examination, the performance was better in subjects with low level of spectral density in the delta band (in the occipital, parietal, central and frontal cortical areas) and high level of the alpha-rhythm spectral density in all the cortical areas, A decrease in performance scores before examination was correlated with an increase in the delta activity (in the right frontal and temporal cortical areas) and rise of the anxiety level (tested by Spielberger).     

Comparative study of the gamma-rhythm in the norm, pre-examination stress and patients with the first depressive episode

The work gives the results of comparative analysis of gamma-rhythm (30-40 Hz) spectral power and synchronization indices in the healthy subjects both in normal situation and before the examination with that of depressive patients with the first episode, in the rest condition and during cognitive tests performance. It is demonstrated that gamma-rhythm spectral power in frontal and temporal areas of depressive patients was significantly higher than that in the norm. In stressful situation the number of differences of healthy subjects from depressive patients decreased in the rest condition and in Kraepelin test. Spatial imagination revealed more significant differences between depressive patients and healthy subjects both in normal and in stressful situations. Gamma-rhythm synchronization level was the same in healthy subjects both in the rest condition and during the tests performance, but in stressful situation it increased in the latter situation as well as in depressive patients. Thus, in the most cases stressful situation decreases the differences of EEG indices between healthy subjects and depressive patients both in the rest condition (by spectral power) and during the tests performance (by both indices). This may point out stress as the "trigger" of depression.     

The variation of two types of spatiotemporal organization of brain potentials at different stages of a cognitive set based on illusory perception of length (Muller-Layer illusion)

The spatiotemporal organization of brain potentials (STOP) under conditions of their multichannel recording was studied was studied in 35 young healthy subjects during formation, actualization, and extinction of the cognitive set on the basis of illusory perception of length (Müller-Layer illusion) by means of quantitative comparison of successive electroencephalotopograms (ET). The ET is an array of momentary values of potentials simultaneously recorded in all the derivations. An ET is characterized by a relief and mean level. Time changes in these characteristics determine a certain type of cortical STOP. Two main types of STOP were revealed. The interaction between these two types of STOP depended on the kind of performance of a subject and was ferlected in the coefficient of dynamic variation (CDV) of ETs. The CDVs were significantly different in subjects with stable and unstable forms of the cognitive set; in the latter this value was higher. The spectral characteristics of the EEG and STOP dynamics were compared. Analysis of power stectra revealed the significant intergroup differences in the alpha 1 frequency range both in the EEG and STOP; the power of this frequency range was higher in subjects with the stable set.     

Changes in the spatial organization of the cortical electrical activity during formation and actualization of a cognitive set to facial expression

Coherence function of the EEG in the bands of 8-13 (alpha rhythm) and 14-25 Hz (beta rhythm) was analyzed in 35 healthy adult subjects during formation and testing of a visual cognitive set to pictures of faces with different emotional expressions. The intra- and interhemispheric coherences of the potentials in the frontal area and coherence between the right frontal and temporal derivation were shown to increase at the stage of set actualization. The results of the analysis confirm the suggestion that the frontal cortical areas are predominantly involved in formation and actualization of the set to facial emotional expression. The conclusion is based on the idea that the spatial synchronization of the brain electrical potentials is an index of the functional relations between the corresponding cortical areas and their cooperative involvement in a certain kind of activity (their simultaneous activation).     

Spectral EEG characteristics in students with different anxiety profile during tests

EEG spectral power was calculated in 39 students at the age of 19-21 years in two experimental conditions: during the common educational process and immediately before an examination (stress condition). During the education process, in subjects with high anxiety (tested by Spielberger) the relative spectral power of the delta activity was higher than in the other group in the occipital, parietal, central, and right frontal brain areas, whereas the power of the EEG alpha in these areas was lower. Before examination tests, in subjects with high activity the delta power bilaterally increased in the temporal areas, whereas in subjects with low anxiety there was a decrease in the alpha rhythm power, especially in the right frontal area. In stress condition, the relative power of the delta activity in both occipital and temporal, right parietal and central areas was higher in subjects with low anxiety, whereas their alpha power was lower in both frontal and in occipital, parietal, and temporal areas of the left hemisphere.     

Segmental structure of the EEG alpha activity in adolescents with disorders of schizophrenic spectrum

The EEG records of 39 healthy adolescents and 45 age-matched schizophrenic patients were analyzed. The broad-band EEG spectral analysis and segmental analysis of the alpha-activity revealed significant differences between the groups. Schizophrenics differed in a decreased spectral power for the alpha2 and betal frequency bands and increased power for the delta and theta bands. Also, in schizophrenic adolescents, quasi-stationary alpha-rhythm segments were longer, and within-segmental EEG amplitudes were higher than in the healthy subjects; the amplitude variability and the steepness of transitions between neighbor segments were increased. The results of the EEG segmental analysis suggest a disintegration of local cortical neuronal ensembles in schizophrenia.     

Reproducibility of swallow-induced cortical BOLD positive and negative fMRI activity

Functional MRI (fMRI) studies have demonstrated that a number of brain regions (cingulate, insula, prefrontal, and sensory/motor cortices) display blood oxygen level-dependent (BOLD) positive activity during swallow. Negative BOLD activations and reproducibility of these activations have not been systematically studied. The aim of our study was to investigate the reproducibility of swallow-related cortical positive and negative BOLD activity across different fMRI sessions. We studied 16 healthy volunteers utilizing an fMRI event-related analysis. Individual analysis using a general linear model was used to remove undesirable signal changes correlated with motion, white matter, and cerebrospinal fluid. The group analysis used a mixed-effects multilevel model to identify active cortical regions. The volume and magnitude of a BOLD signal within each cluster was compared between the two study sessions. All subjects showed significant clustered BOLD activity within the known areas of cortical swallowing network across both sessions. The cross-correlation coefficient of percent fMRI signal change and the number of activated voxels across both positive and negative BOLD networks were similar between the two studies (r ≥ 0.87, P < 0.0001). Swallow-associated negative BOLD activity was comparable to the well-defined "default-mode" network, and positive BOLD activity had noticeable overlap with the previously described "task-positive" network. Swallow activates two parallel cortical networks. These include a positive and a negative BOLD network, respectively, correlated and anticorrelated with swallow stimulus. Group cortical activity maps, as well as extent and amplitude of activity induced by volitional swallowing in the cortical swallowing network, are reproducible between study sessions.     

Psychophysiological mechanisms of stress in subjects with different representation of activation

The EEG spectral power was calculated in 102 students aged 18-25 years in three experimental conditions (during the common educational process, immediately before and after an examination). Before the examination (stress situation), predominant activation of the right anterior cortical quadrant (the area related with negative emotions, according to R. Davidson, 1993) was revealed by the asymmetry coefficient of the beta rhythm. Subjects with low amplitude of the alpha rhythm (more activated) manifested not only emotional but also autonomic disturbances, while only emotional signs were pronounced in students with high alpha (less activated). Increase in the theta rhythm spectral power during stress and its decrease in the poststress period were observed in the less activated persons, which is considered to be a normal reaction to emotionally negative stimuli. On the contrary, in students with low alpha the theta rhythm power in the stress situation was decreased pointing to their emotional instability. In this group, as distinct from the first one, the beta 2 rhythm recorded in the right anterior cortical quadrant did not decrease in the poststress situation. Together with the observed theta rhythm, decrease in the left-hemisphere and bilateral prefrontal areas in the stress situation, this deviation testifies to a predisposition to the reactive depression of these subjects.     

Changes in the EEG spectral power during perception of neutral and emotionally salient words in schizophrenic patients, their relatives and healthy individuals from the general population

To search for EEG-correlates of emotional processing that might be indicators of genetic predisposition to schizophrenia, changes in EEG spectral power during perception of neutral and emotionally salient words were examined in 36 schizophrenic patients, 50 of their unaffected first-degree relatives, and 47 healthy individuals without any family history of psychoses. In healthy persons, passive listening to neutral words induced minimum changes in cortical rhythmical activity, predominantly in the form of synchronization of slow and fast waves, whereas perception of emotional words was followed by a generalized depression of the alpha and beta1 activity and a locally specific decrease in the power of theta and beta2 frequency bands. The patients and their relatives showed a decrease in the alpha and beta1 activity simultaneously with an increase in the power of delta activity in response to both groups of words. Thus, in the patients and their relatives, reactions to neutral and emotional words were ulterior as a result of augmented reactions to the neutral words. These findings suggest that the EEG changes reflect familial and possibly hereditable abnormal involuntary attention. No prominent decrease in reactivity to emotional stimuli was revealed in schizophrenic families.