Organization of neural networks for speech recognition in healthy subjects and its reorganization in patients with poststroke aphasia

Abstract

It has traditionally been accepted that the speech-related brain function is located in some strictly determined areas of the left hemisphere: Broca’s area in the posterior part of the inferior frontal gyrus (Brodmann area 44, BA44) and Wernicke’s area in the posterior part of the superior temporal gyrus (BA22). Modern neuroimaging data including functional magnetic resonance imaging (fMRI) expand our knowledge about speech networks in the brain. Using our own speech tasks (paradigms) with sentence reading and sentence continuation tests, we studied the distribution of the neural speech-related network in healthy subjects and its reorganization in patients with different forms of aphasia. During data processing obtained in the control group we found activation of classic speech areas (Broca’s and Wernicke’s ones) and their right-hemisphere homologues, but the volume of the left-hemispheric activations prevailed. Bilateral activation in the inferior parts of the precentral (BA4) and postcentral (BA1) gyri, in the cerebellar hemispheres, and in the visual cortex (BA17–18) was also revealed. The activation in Broca’s and Wernicke’s speech and speech areas in the group of patients was related to the localization of the brain lesion: in the case of lesion in the corresponding area the activation was shifted towards the stroke area periphery. Additional regions of activation, including the superior parietal lobule (BA7), angular and supramarginal gyri (BA39–40), etc., were recorded in both hemispheres in patients with aphasia. It has been shown that the paradigm used in the current study optimally demonstrates speech-related brain network. The obtained data will help to broaden our comprehension of the brain structures involved in the process of speech and understand their role in the recovery of impaired speech functions.