Dynamics of Alpha Rhythm Peak Frequency during Falling Asleep.

Changes in the frequency characteristics of EEG alpha rhythm in during falling asleep were studied in three healthy individuals under conditions of long-term isolation (MARS-500 project). Falling asleep was preceded by enhanced alpha rhythm frequency. An inverse correlation between the duration of falling asleep and prevailing alpha rhythm frequency during active and relaxed wakefulness was revealed in the left hemisphere. These results demonstrate the principal possibility of predicting the duration of falling asleep by using alpha rhythm spectral analysis. It is assumed that the frequency of the alpha range spectral peak can be a marker of drowsiness and reflect the current need for sleep.

[Perception of Verbal Stimuli in the Norm and in Schizophrenia].

The present study investigates the early stages of selection of meaningful and meaningless verbal-in- formation in an implicit and two explicit tasks by means of the parameters of latency and amplitude of P100 EP component in healthy subjects (n = 99) and in schizophrenia patients with the first psy- chotic episode (n = 102). The obtained results indicate the disturbance of passive perception of meaningful verbal information in psychotic patients. When the instruction is presented patients re- spond similar to norm. The decreased amplitude of P100 component during the,passive perception of words in patients may be related to the severity of hallucinatory behavior. The analysis of changes in the characteristics of the P100 wave in task with instruction as compared to passive perception in the norm revealed a shortening of the time window'of the processing of information regardless to its category and relevance. In schizophrenia patients this feature was found only when reading of the pseudo-words. The results indicate the disturbance of automated attraction of attention to the semantically significant content of the verbal stimulus in the patients' group. The study demonstrat- ed the association between P100 wave characteristics and behavioural responses.

[The Association of Brain-Derived Neurotrophic Factor and Serotonin Transporter Genes with the Parameters of Early Event-Related Potentials During the Passive Perception of Words].

We explored the association of brain-derived neurotrophic factor (BDNF) and serotonin transporter genes with neurophysiological characteristics of the early stages of verbal information processing in the brain in the groups of patients with schizophrenia and schizophrenia spectrum disorders and healthy people. It has been shown that Val66Met and 5-HTTLPR polymorphisms are associated with P100 and N170 during the passive reading of single words written in Russian presented with different occurrence frequency. The healthy carriers of the ValVal genotype (BDN F Val66Met) allele or the SS (5-HTTLPR) genotype performed the task better compared to those with an Met or an L allele. The differences were significant in healthy people and observed as a trend in thepatients.

[Latencies of Sensory and Cognitive Components of Event Related Potentials during Perception of Verbal Stimuli in the Norm and Schizophrenic Patients].

The aim of this work is the study of early and later indices of brain informational processing during the passive reading of concrete words in healthy subjects and schizophrenic patients using the ERP method. Comparative analysis of components P100, N170, P200 and P300 in implicit situation showed that in schizophrenic patients the latency of early components P100 and N170 is shorter while the latency of later components P200 and P300--is longer than in healthy subjects. It could be supposed that the patients have deficit of the early automatic sensory processing of the stimuli revealing through the shortening of their recognition time and this results in the decrease of completeness and preciseness of sensory analysis. In the study there were also revealed negative correlations between the latencies of P100 and P200 components (P200 being a "recognition potential") in healthy subjects confirming the hy pothesis that longer sensory processing of verbal stimuli leads to the shortness of the time for its recognition. For schizophrenic patients the relation between the duration of sensory and cognitive ERP components is disturbed. They have positive correlations between the latencies of early and late components possibly on account of the nonspecific contribution both in early and late components while in normal subjects the early components are more specific than the late ones.

[P100 and N170 Components of ERPs in Abstinent Cannabinoid Users during the Modified Stroop Task].

In the current work we conducted the comparative analysis of P100 and N170 components of ERPs in abstinent cannabinoid users and in healthy controls during the modified Stroop task. The latency of P100 and N170 components was shorter in the temporal, parietal and occipital areas in abstinent cannabinoid users in comparison with the control subjects. The cannabinoid group showed the decrease of P100 amplitude in the right temporal and parietal areas and the decrease of N170 amplitude in the left temporal and parietal areas. There were no differences in the behavioral indices between these two groups. Thus, cannabinoids influence upon the mechanisms of early selection and these alterations of brain activity are stable and long-term.

[Sensory analysis of the words with different occurrence frequency in the norm and in patients with schizophrenia and schizophrenic spectrum disorders].

The paper introduces the study of the early stages of verbal information processing in the brain during the passive reading of single words with different occurrence frequency in Russian and of pseudo-words in healthy subjects and in patients with schizophrenia and schizophrenic spectrum disorders using evoked potentials method. It is shown that the latency of P100 and N170 in healthy subjects increased during visual perception of rare words compared to frequent ones and pseudo-words that apparently reflected the necessity to involve large quantity of brain resources during sensory stages of the processing of the verbal stimulus with intricate semantic. In patients with schizophrenia and schizophrenic spectrum disorders more complicate pattern was observed during the perception of verbal stimuli of various categories. P100 latency was the largest during pseudo-words reading, and P100 amplitude--during frequent words reading in this group. N170 atency in the patients' group was maximal during frequent words reading. Abnormality of evoked potentials polarity in anterior cortical areas most evident during visual perception of meaningful verbal information was also found in these subjects. The obtained results may point to the dysfunction ofprefrontal cortex top-down influence in schizophrenia and schizophrenic spectrum disorders, which is manifested in the disturbed sensory processing ofvarious categories verbal stimuli.

[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.

[Temporal characteristics of the initial stage of the verbal information processing in healthy subjects and in schizophrenia].

The study aimed to investigate the early coding of visually presented words and pseudowords using event-related potentials (ERP). We conducted comparative analysis of the characteristics of P100 and N170 in healthy controls and in patients with the first episode of schizophrenia during passive perception of verbal stimuli as well as under conditions of relevant words and pseudowords. The latency of early ERP components P100 and N170 appeared to be shorter in comparison with healthy subjects in the temporal, parietal and occipital areas. The latency of P100 in patients was significantly shorter in the temporal, parietal and occipital areas, whereas the latency of N170 was shorter in the parietal and occipital areas than in controls. The latency of N170 in healthy subjects was significantly longer to words than to pseudowords and in patients - vice versa. The latencies of N170 in all TPO areas were equal in healthy subjects during word processing, and this equality was upset during non-word processing. In patients with schizophrenia the equality was upset, but, opposite to healthy patients, the upset of equality was more expressed during words processing. Thus, the early stage of verbal information processing in schizophrenic patients is insufficient in time. The time deficit of the automatic processes may lead to defective processing of overall information.

[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.

[Gamma-rhythm, positive, negative symptoms and cognitive dysfunction in schizophrenia].

We studied characteristics of gamma-band (30-40 Hz) EEG in dependence on the prevalence of positive or negative symptoms of schizophrenia, taking into account the state of cognitive functions. Twenty patients with ICD-10 diagnosis of schizophrenia, with different disease duration (first episode and duration of more than two years) and 38 healthy people were studied. The presence and intensity of positive and negative symptoms were measured by the PANSS scale and cognitive functions were assessed using neuropsychological tests. Compared to the controls, the gamma-rhythm power was higher in patients with the prevalence of positive symptoms and lower in patients with negative symptoms. The reduced number of coherent relations, in particular, interhemispheric ones, and the absence of gamma-band synchronization in different brain areas were found in patients as well.

Comparative study of the gamma rhythm in normal conditions, during examination stress, and in patients with first depressive episode.

We report here a comparative analysis of measures of spectral power and synchronization of the gamma rhythm (30-40 Hz) in healthy subjects in normal conditions and before examinations (a stress situation) and in patients with major depression (first episode), both without cognitive loading and during performance of tests (arithmetic counting and spatial imagination). The results showed that the power of the gamma rhythm in the frontal and temporal areas of the cortex was significantly greater in patients with depression than in normal subjects. In the stress situation, healthy subjects showed a reduction in the number of differences in this measure as compared with depression patients, both at rest and during performance of the arithmetic counting test. the spatial imagination test resulted in a smaller number of significant differences between patients with depression and healthy subjects, regardless of whether the latter were in normal conditions or in the stress situation. The levels of gamma rhythm synchronization between cortical areas at rest and during cognitive loading were not different in healthy subjects, though synchronization increased in healthy subjects during stress and in patients with depression. Thus, the stress situation in healthy subjects leads to decreases in the differences in EEG measures from those in depression both at rest (power) and during cognitive loading (both measures). This may be evidence that stress is a "trigger mechanism" for depression.

[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.

Relationship between EEG power and rhythm synchronization in health and cognitive pathology.

We report here studies of comparative measures of spectral density and cortical interactions in EEG rhythms in health and schizophrenia. In healthy subjects, all rhythms were symmetrical and synchronous. In "acute" schizophrenia, unlike the situation in health, there was asymmetry (predominantly right-sided) in the distribution of the spectral power of EEG rhythms. In chronic patients, asymmetry was less marked, though the power of most EEG rhythms was significantly lower than in the other two study groups. "Acute" patients showed a lack of interhemisphere interactions for all rhythms apart from the alpha rhythm, while the number of cortical interactions in chronic patients was rather lower than that in the "acute" patients, though there were significantly fewer than in healthy subjects. In addition, the gamma range showed only one interhemisphere association in the posterior areas. These neurophysiological characteristics may underlie a number of the impairments of mental activity in patients with schizophrenia. These data may also indicate that the linkage between power characteristics and synchronization of EEG rhythms is a necessary condition for normal perceptive and cognitive activity and the organization of behavior.

[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.