Organization of language network in healthy subjects and its reorganization in patients with poststroke aphasia

Abstract

It’s a traditional belief among neuroscientists that the speech function is located in some strictly definite areas of the left hemisphere: Broca’s area in the rear part of the lower frontal gyrus (Brodmann area 44, or BA44), and Wernicke’s area in the rear part of the upper temporal gyrus (BA22). However, data collected with the contemporary neurovisual research methods, in particular, with functional magnetic resonance imaging (fMRI), disprove the localizationist theory of speech. With the specially designed speech task (paradigm) consisted of sentence reading and sentence continuation tests, we researched distribution of speech neuron network in healthy people and its reorganization in patients with different types of aphasia. After processing of control sample data, we noticed activation of classic speech areas (Broca’s and Wernicke’s) and their right hemisphere homologies. However, the amount of activations was predominant in the left hemisphere. We also noticed bilateral activity in lower parts of pre-central (BA4) and post-central (BA1) gyri, in cerebellum hemispheres and in visual cortex (BA17–18). In stroke patients activation in Broca’s and Wernicke’s areas depended on a lesion location. Activation wasn’t registered in case of damage of corresponding region, but it was migrated on perilesional area. We revealed new regions of activity at patients with aphasia, including upper parietal gyrus (BA7), angular and over-marginal gyri (BA39–40). Aforementioned activations were disclosed both in left and right hemispheres. The research shows that the speech paradigm used demonstrates functioning of speech system in the optimal way. The received data will increase understanding of brain structures involved in process of speech and their importance for recovery of damaged speech functions.