Abstract
Stroke lesions in the language centers of the brain impair the language areas and their connectivity. This article describes the dynamics of functional connectivity (FC) of language areas (FCL) during real-time functional magnetic resonance imaging (RT-fMRI)-based neurofeedback training for poststroke patients with expressive aphasia. The hypothesis is that FCL increases during the upregulation of language areas during neurofeedback training and that the training improves FCL with an increasing number of sessions and restores it toward normalcy. Four test and four control patients with expressive aphasia were recruited for the study along with four healthy volunteers termed as the normal group. The test and normal groups were administered four neurofeedback training sessions in between two test sessions, whereas the control group underwent only the two test sessions. The training session requires the subject to exercise language activity covertly so that it upregulates the feedback signal obtained from the Broca's area (in left inferior frontal gyrus) and amplifies the feedback when it is correlated with the Wernicke's area (in left superior temporal gyrus) using RT-fMRI. FC was measured by Pearson's correlation coefficient. The results indicate that the FC of the test group was weaker in the left hemisphere than that of the normal group, and post-training the connections have strengthened (correlation coefficient increases) in the left hemisphere when compared with the control group. The connections of language areas strengthened in both hemispheres during neurofeedback-based upregulation, and multiple training sessions strengthened new pathways and restored left hemispheric connections toward normalcy.
Highlights
Aphasia or loss of speech is the most prevalent disability in stroke survivors
The functional connectivity (FC) networks obtained among the modules during each of the training sessions are shown for test and normal groups in Figures 3 and 4
For the normal group during intergroup comparison (A) normal group > test group, it was observed that the FC was high between modular pairs central opercular (CO)–CO.r, frontal language (FL)–temporal language (TL), and SP–CO (Fig. 5a)
Summary
Aphasia or loss of speech is the most prevalent disability in stroke survivors. Stroke lesions affecting the Broca’s area (inferior frontal gyrus or IFG), Wernicke’s area (superior temporal gyrus or STG) and connecting white matter tracts, can lead to aphasia. Aphasia can be broadly classified as Broca’s aphasia (failure to express language), Wernicke’s aphasia (failure to comprehend language), or conduction aphasia (Dronkers and Baldo, 2010). In Broca’s aphasia or expressive aphasia, the expression of speech is reduced and is limited to short sentences of very few words and is referred to as telegraphic speech. The linking of words to form sentences is severely affected and agrammatical. Vocabulary access is limited, and speech generation is laborious and nonfluent. The person may comprehend speech relatively well and be able to read well; the ability to write is limited. Lesions in the Broca’s area in the IFG, the lower part of the precentral gyrus, and the opercular and insular regions are associated with
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