NEUROPHYSIOLOGICAL MECHANISMS OF SPEECH PERCEPTION AND THEIR PERCULARITIES IN HEALTHY CHILDREN AND CHILDREN WITH DEVELOPMENTAL DISORDERS

Neuronal synchronization, reflected in the EEG pattern, is the mechanism by which the brain integrates different types of information contained in a speech message and presented in different areas of the brain (for example, phonological, spelling, semantic and syntactic information). The process of understanding a sentence consists of two groups of interrelated cognitive operations: it begins with searching in memory for phonological, syntactic and semantic properties of words, which is followed by integrating information into a general idea of the sentence meaning. The stage of searching for words in adults results in an increase in the theta rhythm power. The stage of integrating words into a sentence results in the growth of theta, beta, and gamma rhythms. At the same time, the growth of theta rhythm is more typical for children than for adults. Higher rhythms reactivity during speech perception indicates better developed speech skills in children. Under conditions of relative relaxation, the EEG of children with a high level of speech development is characterized by a moderate power level of theta and beta rhythms and a high level of alpha and mu rhythms. It is assumed that a key role in the process of understanding speech is played by the so-called «action perception circuits», surrounding the Sylvian sulcus of the left hemisphere. The «action perception circuits» are composed of nerve cells capable of providing the speech signals perception and generation. The most important subgroup of neurons included in the «action perception circuits» are mirror neurons that are activated when performing and observing actions. The desynchronization of the EEG mu rhythm is considered as mirror neurons activation marker. In several studies, it revealed that the level of mirror neurons activation and the level of speech understanding in children are connected. It is a topic of great interest to research the mu rhythm alpha and beta components reactivity both during the production of speech and during the perception of another person speech. At present, it is becoming obvious that analyzing the EEG rhythms power changes during the speech understanding in different scenarios could be used to identify the mechanisms of the brain language network and speech disorders. The revealed patterns make it possible to propose ways of correcting the children speech development using EEG biological feedback methods.