Organization of Cortical Regional Interactions during Word Derivation Task
We analyzed the spatial-temporal structure of interregional interactions of cortical bioelectric potentials (so-called functional connectivity) during subvocal generation of Russian stem words. In the derivational task, the subjects had to covertly generate stem words after the presentation of the noun. Correlation and coherence analyses of multichannel electroencephalograms (EEGs) showed a significant increase of intrahemispheric interactions within the left hemisphere during derivation task in adults. The activation of left fronto-temporal-parietal regions indicates that these areas are involved in the covert generation of stemwords. Moreover, we observed a significant decrease in the hemispheric interactions between temporal, temporo-parieto-occipital (TPO), inferofrontal, and occipital areas of both hemispheres, especially for the right inferior frontal zone. Our previous studies [24, 33, 34] showed that verbal processing requires joint and extremely coordinated activities of both hemispheres. The hemispheric interactions during the perception of sentences with syntactical or semantic mistakes were increased significantly as compared to eyes-closed resting state. At the same time, we observed almost no changes in intrahemispheric EEG correlations. Phonemic synthesis was associated with a more significant increase in the contralateral interactions in the left hemisphere; the generation of sentences from words, in the right hemisphere. Thus, the data obtained in this study indicate that active word derivation processes provides pronounced lateralization of the neurophysiological mechanisms. The current data expand the modern concepts about brain mechanisms of verbal activity at the morphological level of language.