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.     

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.     

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.     

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.     

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.     

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.