Identification of Neurophysiological Markers of Verbal Information Processing Using Cognitive Evoked Potentials for Studying Schizophrenia Spectrum Disorders.

Materials and Methods: Cognitive evoked potentials were studied in 40 students of higher school with high and low (control) scores obtained on the Schizotypal Personality Questionnaire (SPQ) in response to the presentation of visual verbal information in the form of agreed word-combinations. In the first series of presentations, it was necessary to refer the attribute to one of the categories and to read the noun silently (non-target condition). In the second series, the attribute should be read silently, and then the following noun has to be categorized (target condition). There has been performed a cluster analysis of the evoked potential curves obtained in response to the noun presentation in the target and non-target conditions in the groups of participants with high and low scores gained on SPQ. Results: Processing of the verbal stimulus under passive reading conditions and under the conditions of word categorization within the frameworks of a simple context has shown that in the group with low scores on the schizotypal questionnaire, lateralization of the N150 component to the left side was observed in contrast to the group with high scores. In this group, increase of the N400 component amplitude was found in response to the words presented for their passive reading in comparison with the categorization condition. On the contrary, in the group with high schizotypy scores, the N400 component appeared to be insensitive to the type of the task, i.e. neurophysiological differences were not expressed between reading and performing stimuli categorization task. These persons were found to have the decreased amplitude of the late positive component as compared to the control group under the condition of passive reading of the words. Increase of the late negative wave amplitude was registered in response to the target words subjected to categorization in comparison with reading in both groups of participants. Insufficiency of language lateralization and deficit connected with the language networks being activated automatically at the initial stage of word recognition are observed in the examined persons with schizotypy. Additionally, processing of the information in these persons at the stage of lexical-semantic processes is weakly modulated by the task imposing different requirements on the level of mental activity control. Some reduction of mnestic process activation is also possible, which is manifested during passive reading of the words, but not in the conditions of their categorization. Conclusion: The research conducted may serve as a starting point for a more detailed and long-term study of the fundamental mechanisms of impairment in information processing in the course of clinically evident pathology formation. In the applied aspect, the work may be considered as a contribution to the ongoing search for neurophysiological markers for early diagnosis of schizophrenia spectrum disorders.