Identification of brain region associated with verbal function using electroencephalography signals — A step toward the treatment of aphasia

A research group led by Professor Natsue Yoshimura of the Department of Computer Science, School of Computing at the Institute of Science Tokyo, Professor Ryuichiro Hashimoto of the Graduate School of Humanities at Tokyo Metropolitan University, and Tomoya Gyoda of Ghoonuts (Kyoto City, Kyoto Prefecture) has announced that they located a brain region related to concerned with the production of speech using electroencephalography signals. They confirmed that electrical stimulation of the specified brain region using transcranial direct current stimulation (tDCS) improves language function. The technique is expected to find application in treating aphasia. The results were published in the international journal Neuroimage on January 28.

Aphasia is a language disorder whose symptoms include "inability to recall names of things" and "inability to comprehend spoken language." The symptoms of aphasia persist for patient's entire life in many cases. Aphasia occurs in about 30% of patients who have survived a stroke, and about 500,000 people in Japan are estimated to have aphasia.

As a new treatment for aphasia, tDCS from the scalp targeting Broca's area, a brain region related to object naming, has been reported to hold the potential to improve language functions. tDCS is a technique for modulating neuronal excitability and inhibition by applying weak electrical stimulation from the scalp. It is characterized by the requirement for only a simple device. Meanwhile, brain regions that are active during language tasks, such as naming, vary greatly from person to person. Functional magnetic resonance imaging (fMRI) has recently been proposed to locate a region to simulate each individual, but it is not very versatile.

In this study, the research group examined whether the active regions in each individual can be determined by electroencephalography, which is highly versatile in clinical practice. Healthy adults used electroencephalography to measure brain activity during naming, followed by a signal source estimation method, which uses machine learning to estimate the brain cortex activity to locate active regions for each individual. They compared the results with the regions identified by fMRI and confirmed a high agreement rate between electroencephalography and fMRI.

tDCS stimulation of regions identified by electroencephalography significantly shortened the response time in naming compared to tDCS targeting Broca's area or sham stimulation. The response time was shortened by 40 milliseconds on average. If the highly versatile electroencephalography can be used to identify active areas for each individual, treatment of aphasia may become possible at medical institutions that do not have MRI equipment.

Moving forward, the research group aims to improve the brain function of aphasia patients by finding the optimal tDCS conditions for each individual. Yoshimura said, "The fact that tDCS improved reaction speed suggests the possibility that individual differences in broad brain regions involved in language function can be visualized using electroencephalography signals measured on the scalp. I believe this is a valuable step in demonstrating the possibility that visualization of the association of activity in different brain regions with specific symptoms of aphasia can contribute to developing more effective therapeutic strategies and elucidating etiology.

Journal Information
Publication: Neuroimage
Title: Electroencephalography-guided transcranial direct current stimulation improves picture-naming performance
DOI: 10.1016/j.neuroimage.2024.120997