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

Abstract

Its a traditional belief among neuroscientists that the speechfunction is located in some strictly definite areas of the left hemisphere:Brocas area in the rear part of the lower frontal gyrus(Brodmann area 44, or BA44), and Wernickes area in the rearpart of the upper temporal gyrus (BA22). However, data collectedwith the contemporary neurovisual research methods, in particular,with functional magnetic resonance imaging (fMRI),disprove the localizationist theory of speech. With the speciallydesigned speech task (paradigm) consisted of sentence readingand sentence continuation tests, we researched distribution ofspeech neuron network in healthy people and its reorganizationin patients with different types of aphasia. After processing ofcontrol sample data, we noticed activation of classic speech areas(Brocas and Wernickes) and their right hemisphere homologies.However, the amount of activations was predominant in theleft hemisphere. We also noticed bilateral activity in lower partsof pre-central (BA4) and post-central (BA1) gyri, in cerebellumhemispheres and in visual cortex (BA1718). In stroke patientsactivation in Brocas and Wernickes areas depended on a lesionlocation. Activation wasnt registered in case of damage of correspondingregion, but it was migrated on perilesional area. Werevealed new regions of activity at patients with aphasia, includingupper parietal gyrus (BA7), angular and over-marginal gyri(BA3940). Aforementioned activations were disclosed both inleft and right hemispheres. The research shows that the speechparadigm used demonstrates functioning of speech system in theoptimal way. The received data will increase understanding ofbrain structures involved in process of speech and their importancefor recovery of damaged speech functions.

Keywords

• fmri
• aphasia
• speech paradigm
• stroke