EEG-guided tDCS shows potential for innovative therapies in language disorders

Electroencephalography (EEG) may offer a more accessible alternative to functional magnetic resonance imaging (fMRI) for guiding transcranial direct current stimulation (tDCS) when treating aphasia. Researchers from Institute of Science Tokyo found an 80% agreement between EEG and fMRI in identifying brain regions activated during language tasks. Furthermore, EEG-guided tDCS improved picture-naming speed in participants, indicating its potential for innovative therapies in language disorders.

Many neurological disorders are directly linked to damage or deterioration in specific regions of the brain. For example, aphasia-a disorder characterized by impaired language abilities-is often caused by problems in Broca's area, which is a region of the brain concerned with the production of speech. Although available therapies for aphasia are quite limited, scientists have been reporting functional improvements in patients by using transcranial direct current stimulation (tDCS).

Briefly put, tDCS involves the application of a low electrical current to the scalp to modulate neuronal activity, aiming to enhance or suppress specific brain functions. Today, functional magnetic resonance imaging (fMRI) is the most powerful tool available to pinpoint functional areas in the patient's brain. However, fMRI requires large, expensive facilities and dedicated specialists, rendering this approach impractical for routine clinical applications. But what if there was a more accessible way of identifying specific functional regions of the brain, like Broca's area?

In a recent study, which was published online in NeuroImage on January 6, 2025, a research team led by Professor Natsue Yoshimura of Institute of Science Tokyo (Science Tokyo), Japan, explored the potential of electroencephalography (EEG) as a tool to guide tDCS.

EEG measures the activity of neurons as electrical potentials on the scalp. It has the advantages of being relatively inexpensive and portable. If its disadvantage of low spatial resolution is overcome, EEG may thus offer a promising alternative to fMRI for determining sites for tDCS."

Professor Natsue Yoshimura of Institute of Science Tokyo (Science Tokyo), Japan

To test this hypothesis, the research team conducted two separate experiments. In the first one, they acquired EEG and fMRI data from 21 healthy participants as they completed picture-naming tasks. In these tasks, participants had to say the name of the object shown in a photograph as quickly as possible. The researchers then compared the activated areas of the brain identified based on either EEG or fMRI measurements. Interestingly, they found a remarkable 80% agreement between both methods, supporting the hypothesis.

In the second experiment, the researchers investigated whether tDCS applied to functional areas identified via EEG could improve performance in picture-naming tasks among 15 healthy participants. Compared to the standard approach, in which tDCS is applied directly to Broca's area as determined by considering the conventional geometrical position, EEG-guided tDCS led to a marked improvement in picture-naming speed.

Together, these findings not only confirm the team's hypothesis but also underscore the significant potential of EEG in improving language functions, which may contribute to the enhancement of the rehabilitation process for aphasia. "Our study provides the first indication that EEG-guided tDCS, considering the significant individual differences in brain activity, has the potential to be more effective in improving language function than conventional tDCS methods targeting Broca's area in people with aphasia. The results also suggest EEG-based analysis may be effective for identifying brain areas relevant to specific cognitive tasks," concludes Yoshimura.

Continued advancements in this field will hopefully lead to effective therapeutic strategies for people affected by aphasia.