[Comparative EEG-study of normal and autistic children].

The work represents the results of a comparative study of a spectral power as well as averaged coherence in theta and gamma-EEG band in a healthy and autistic boys (the mean age 6 years 1 month). Healthy boys showed a decreasing in theta spectral power as well as in averaged coherence, and increasing in gamma spectral power as well as in averaged coherence during cognitive task. Spectral power of gamma band shows more high scores in autistic boys than in normal ones. Cognitive task situation do not change spectral power of the fast oscillations in autistic children. Spectral power of theta--band shows more low scores in autistic boys than in normal ones. Cognitive task situation do not change spectral power and averaged coherence of theta oscillations in autistic children.

[Analysis of event-related potentials to verbal stimuli in healthy subjects and schizophrenia patients].

In 30 healthy subjects and 32 patients after the first episode of schizophrenia 19 channel-EEG was recorded during visual presentation of a random sequence of words and pseudo-words. In the first series of the experiments, subjects had to read the presented verbal stimuli, in the second series they had to press a button when seeing a word, and in the third series they were instructed to press the button when seeing a pseudo-word. We studied components N170, P300 and N400. In the group of healthy subjects, the amplitude of N170 increased to words in the situation of their relevance, which corresponds to the "recognition potential", whereas in the group of patients, the amplitude of N170 increased to pseudo-words when they were relevant. So it was a paradoxical response. The amplitude of the ERP later waves (P300 and N400) in the group of schizophrenic patients was smaller and the relevance effect was impaired when the target stimuli were pseudo-words. However, the incongruity effect consisting in an increase in N400 amplitude to a non-target stimulus remained intact in patients.

[Adaptive method for EEG spectrum component decomposition].

A new computerized method for EEG rhythms extraction is proposed as a development of the idea of adjustable boundaries of frequency components that was put forward in previous investigations. Principle component analysis of the correlation matrix of EEG spectra with subsequent rotation of factor solutions was used for decomposition of a spectrum into physically meaningful spectral components. The method was tested on EEG of 14 healthy subjects recorded in 17 functional waking states. Fourteen independent spectral components in the spectral range from 0 to 100 Hz were extracted and their frequency boundaries were consistent with the current knowledge on frequency components of EEG oscillations. Main advantage of the described method is the adjustable estimation of EEG frequency oscillators taking into account characteristic properties of individual EEGs. Possible area of application might be the correct evaluation of spectral power of the EEG rhythms, EEG coherence and other spectral characteristics in clinical and experimental research, studies of the frequency characteristics of the EEG rhythms in different human functional states, changes in frequency characteristics of the EEG rhythms during maturation and in mental pathology.

[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.

[Peak alpha frequency and psychopathological symptoms in schizophrenia].

Spectral characteristic of the alpha activity (frequency of the maximum spectral peak) were comparatively studied in schizophrenic patients with predominance of positive or negative symptoms and healthy subjects in the resting state and during cognitive task performance. In patients with negative symptoms, the spectral peak frequency of the alpha activity (8-13 Hz) was decreased at rest as compared to healthy subjects in all cortical areas. In patients with positive symptoms, the peak frequency of the alpha rhythm in the occipital cortical areas was higher than in healthy subjects. The performance-induced increase in the alpha-rhythm peak frequency during cognitive tasks was less expressed in schizophrenics than in healthy subjects. A correlation of these characteristics with psychopathological symptoms was revealed. The results suggest a difference in neurophysiological mechanisms underlying positive and negative symptoms in schizophrenia.

[Prepulse modification of acoustic startle reaction in patients with schizophrenia and healthy controls].

Prepulse modification of acoustic startle reaction (ASR) was studied in patients with schizophrenia and healthy controls according to the protocol recommended by the Consortium on the genetics of schizophrenia. Patients displayed the reduced ASR magnitude of prepulse inhibition (PPI) and increased startle latency prepulse facilitation (PPF) at 60 ms lead interval. The ASR amplitude PPF at 2500 ms lead interval was also impaired in patients. Effects of the recent head trauma and psychoactive drug experience on the ASR prepulse modification were different in patients and controls. The high baseline amplitude and short ASR latency in patients were correlated with the excitation level measured with the PANSS (item P4) whereas the PPF reduction was correlated with the high total score on the PANSS positive subscale. These results suggest the possibility of using ASR prepulse modification in clinical neurophysiology.

[Processing of visually presented verbal stimuli in evoked potentials].

The ERPs to familiar, unfamiliar, and recently learned words were recorded in 20 right-handed students who have recently studied a course in sensory physiology during performance of two tasks. The first task consisted in processing of different types of words, the second task required recognition of terms from sensory physiology. In the first task, three types of words were presented to a subject: familiar words related and unrelated to a given category and unfamiliar words. Subjects had to press the appropriate button responding to the questions whether they considered the presented word be related to the given category and whether they were sure in their answer. In the second task, terms from recently studied physiological material were presented to the students who had to detect whether those terms were related or unrelated to the given sensory system. Significant differences between late ERP components were revealed by Student test for matched samples. In the first task, component N400 of the ERP to unfamiliar words was higher than that of the ERP to familiar words. It was also higher in ERPs to words unrelated to the given category than in ERPs to related words. However, this component did not differ between ERPs to well and poorly acquired words in the test on sensory physiology. On the contrary, the late positive component was more expressed in ERPs to familiar and better acquired words in both tasks. Brain mechanisms of processing of different types of words are discussed.

[Effect of support removal on pre-saccadic EEG potentials in test-subjects with various asymmetry profiles].

Saccades and slow pre-saccadic potentials were investigated in 12 volunteered test-subjects (7 subjects with the leading right eye (RE-group) and 5 subjects with the leading left eye (LE-group) before and after 6-d DI experiment. Visual stimulation was provided with 3 LEDs one of which was located centrally in the field of vision and the other two - 10 degrees left and right along the horizontal axis. The subjects performed the test for antisaccades requiring to produce saccades toward a point symmetrical to displayed stimulus. EEG (monopolar in 19 standard leads) and electrooculogram were registered. Peripheral stimulus activation served as a trigger for backward averaging as a method to obtain slow pre-saccadic potentials (PSPs). Testing before immersion did not reveal any noteworthy differences in saccades produced by the members of both groups. At the same time, amplitude of pre-saccadic negativity (PSN) in LE-group was lower, especially in the frontal region of head, and distinguished by apparent asymmetry throughout the period of analysis. In immersion, latent saccades and percentage of erroneous reactions did not change in the RE-group but increased in the LE-group. Both groups reduced the PSN amplitudes shifting PSN to the right cerebral hemisphere; differences between the groups were masked by immersion. The RE-group was marked by a reliable decline of the PSN amplitude in the frontal leads due to, probably, sensory disintegration and reduced tonic afferentation in immersion. In the LE-group, maximum PSN amplitude was registered in the central region of head equally before and during immersion.

[The multipleparameter combinatory analysis of EEG rhythms in norm and at schizophrenia].

On the base of EEG records of 38 healthy subjects and 17 schizophrenic patients the statistical structural analysis of 176 elementary characteristics in all 11 spectral ranges for each of 4 experimental conditions was carried out, employing "Kora-n" recognition algorithm, adopted for EEG analysis by Kaplan. The list of characteristics with a minimal error revealed statistically significant differences between spectral power of delta- and theta-ranges in healthy subjects and schizophrenic patients. Spectral power of these slow rhythms was always higher in the formers then in the latter. As a whole, in schizophrenic patients the decrease of delta-rhythm spectral power in the lower frontal area of right hemisphere and theta-rhythm - in the lower temporal area of left hemisphere most frequently is observed. These results are in agreement with hypofrontality and hypotemporality characteristic of schizophrenic patients and testify to the lack of "fundamental" brain base of cognitive functions. These facts are evidently connected with the significant neurochemical disturbances taking place in schizophrenia.

[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.

[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.

[Spectral power and cortical interactions in the beta2 rhythm in normal subjects and schizophrenic patients]. / Spektral'naia moshchnost' i vnutrikorkovye vzaimodeistviia po beta2-ritmu v norme i pri zhizofrenii.

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.

[Cortical interactions in the beta2-rhythm during examination stress]. / Issledovanie urovnia vnutrikorkovogo vzaimodeistviia v beta2-diapazone pri ékzamenatsionnom stresse.

Two groups of students: with higher and lower amplitudes of the baseline alpha-rhythm differed in the level of anxiety during examinations and the level of cortical interactions. Cognitive tasks were presented in three experimental conditions: before the examinations, immediately after the examinations, and on a usual day of academic semester (control). Subjects with initially higher alpha-rhythm amplitude had lower level of anxiety in a stress situation. Cognitive performance of these subjects before examinations was associated with an increase in the number of functional connections between different cortical areas. In the subjects with initially lower alpha-rhythm amplitude, the level of cortical interactions before examinations was higher, but presentation of the cognitive task led to a decrease in the number of intracortical connections. However, the localization of these connections was task-specific.

[Cortical connectivity in schizophrenic patients with positive and negative symptoms ]. / Korkovye sviazi u bol'nykh shizofreniei s pozitivnymi i negativnymi simptomami.

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.

[The noncoherent components of evoked brain activity]. / Nekogerentnye sostavliaiushchie vyzvannoi aktivnosti mozga.

Poststimulus spectral EEG changes and their correlation with evoked potential (EP) were analyzed. The non-stationary components of the brain evoked activity were revealed in 32 volunteers during simple motor reaction and choice reaction to visual stimuli. This nonstationary activity was manifested in poststimulus changes in the mean wave half-period duration (MWHPD) and mean wave half-period power of the delta- and beta-frequency oscillations computed in the EEG realizations after the EP subtraction. The latencies of high-frequency EP components fell into the intervals of the MWHPD decrease and increase in the power of beta-oscillations, and the latencies of low-frequency EP components coincided with the intervals of the MWHPD increase and decrease in the power of delta and beta-oscillations, which pointed to correlation of these changes with the EP.

[The disordered organization of the cortical processes in depression]. / Narushenie organizatsii korkovykh protsessov pri depressii.

The study of depressive patients with the method of the EEG mapping revealed some stable differences from the norm. Firstly, in depression there are the disturbances of the definite cortical zones' activation: the right anterior and the left posterior cortical parts are hyperactivated while the left anterior and the right posterior-- relatively inhibited, evidently causing the informational processing disturbances. The important link of these disturbances--the disconnection of the anterior and the posterior cortical regions that could be called "transversal functional blockade". The second feature of the electrical activity of the brain in depression is the absence of the high frequency component of alpha-rhythm, that evidently in normal conditions is connected with the positive emotions mechanisms. The third feature is the difference in arousal reaction in the alpha- and beta-bands frequencies.

[An analysis of evoked brain activity by computing the average duration of the wave half-period]. / Analiz vyzvannoi aktivnosti mozga putem vychisleniia srednei dlitel'nosti poluperioda kolebanii.

Poststimulus spectral EEG changes and their relation to averaged evoked potential (AEP) were analysed using average wave half period length (AWHL) computation method. In 5 healthy subjects increase of AWHL in the latency range of slow AEP components was revealed during simple motor reaction to visual stimuli. It was shown that AWHL increase could not be explained by AEP contribution to single realizations and/or by the process of suppression of EEG rhythms.