Psychophysiological mechanisms of internal pronunciation of words in people with stuttering

The identification of psychophysiological mechanisms underlying internal pronunciation in healthy individuals may enhance the performance of modern brain–computer interfaces that rely on the recognition of mental commands. Studying the brain mechanisms of internal pronunciation in people with stuttering can contribute to understanding the causes of this speech disorder and to developing new or improving existing methods of stuttering correction. The purpose of the study was to compare the psychophysiological mechanisms of internal speech (internal pronunciation) and word perception in people with normal and speech defects (stuttering). Electroencephalographic (EEG) recordings were obtained from 35 participants (25 with normal speech and 10 with stuttering) using a 19-channel system while they performed a task involving listening to and internally pronouncing four words in Russian (“sakhar”, “shashlyk”, “raketa”, and “r’aketa”). The analysis was carried out using a novel tool – the virtual implanted electrode technique (Patent RU 2,785,268 C1 by A.V. Vartanov), which enables the reconstruction of neural activity across several brain regions, including six areas of interest: Broca’s area, Wernicke’s area and their right-hemisphere homologues, as well as the cerebellum bilaterally. The activity data obtained were compared in control (normal) groups and people with stuttering. The comparison revealed significant differences in reconstructed electrical activity with an emphasis on hyperactivation in stutterers of the Broca’s area, the symmetrical zone on the right, and the cerebellar cortex bilaterally, compared with the control group, when listening and pronouncing words internally. In this way the process of perception and internal pronunciation of words in a group of normals and stutterers is different. The significant differences observed in Broca’s area likely reflect its primary role in speech production, whereas differences in the cerebellar cortex may be related to its supportive function in the motor coordination of speech. The absence of differences in the Wernicke’s zone can be considered as a consequence of the lack of auditory feedback during internal pronunciation.