[Evoked spectral EEG power during presentation of pseudowords and words from "animate" and "inanimate" categories].

Pseudowords and words of "animate" and "inanimate" categories were shown to healthy young adults (14 women and 9 men) in three series. In the first series, subjects were just reading presented verbal stimuli (words and pseudowords), in the second series, they had to click a mouse button in response to presentation of a word, and in the third series they clicked a button when pseudowords were presented. Presentation of words and pseudowords caused desynchronization of the alpha rhythm and synchronization of the theta rhythm. Early synchronization (50-250 ms) was stronger for pseudowords and words of "animate" category during passive perception of stimulus. The middle synchronization period (250-800 ms) was stronger in projections of Broca's and Wernicke's areas. The relevance of the stimuli led to an increase in desynchronization and reduction of early and late (800-1500 ms) synchronization periods after presentation of both words and pseudowords. For words of "animate" categories, the synchronization of the theta rhythm was more pronounced in the early periods, and for words of "inanimate" categories, the theta rhythm synchronization was more distinct in the middle periods.

[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.

[Verbal stimuli semantics and relevance of ERPs].

In 22 healthy participants EEG from 28 channels was recorded during visual presentation of a random sequence of words and pseudo-words. The experiment consisted of three parts. In the first part the subjects just passively read the stimuli, in the second part they had to click the mouse button when seeing a word and in the third part--when seeing a pseudo-word. The results show that words are more significant to subjects than pseudo-words causing higher amplitude of P100 and P300 in the first and the second parts of the experiment, evidently, due to presence of meaning. However, the lexical task may be a more significant factor of the information processing than the presence of meaning, since in the third part of the experiment, where pseudo-words were relevant, they elicited higher amplitude of P300 than words. Pseudo-words elicited also negative N400 amplitude than words, revealing incongruity effect. However, when words were task-incongruent, this effect is significantly less evident.