Electrical stimulation against aphasia

Individually selected stimulation helped improve speech after stroke

Elizaveta Ivtushok, N+1

Canadian scientists have successfully tested individually selected transcranial micropolarization on patients with aphasia received after a stroke in the left hemisphere. They managed to restore normal activity in the gamma and theta ranges in the areas near the foci of stroke and in the corresponding areas of the right hemisphere: after stimulation, patients could repeat 61 percent more complex words shown to them.

Micropolarization of areas untouched by stroke in the future can help speed up the process of rehabilitation and speech recovery, scientists write in Scientific Reports (Shah-Basak et al., High definition transcranial direct current stimulation modulates abnormal neurophysiological activity in post-stroke aphasia).

Aphasia (acquired speech disorder) is most common in people who have experienced a stroke with a focus in the left hemisphere of the brain: according to various estimates, speech problems are observed in 21-38 percent of patients. To restore speech functions, patients undergo long–term rehabilitation, and in addition to standard therapy (classes with a specialist), brain stimulation may be useful in it, but so far it is not widely used in clinical practice - largely due to the shortcomings of the developed protocols.

Jed Meltzer from the University of Toronto and his colleagues suggested that individually tuned stimulation can work most effectively in the rehabilitation of aphasia. Their study involved 11 patients who had suffered a stroke in the left hemisphere: all of them were diagnosed with aphasia, although the types of the disorder were different. Before starting the study, the participants took a test to assess their speech abilities: they were shown words (six patients – complex, five – simpler words) and asked to repeat them aloud after a short delay. The participants' brain activity at this time was measured using magnetoencephalography (MEG). In particular, the scientists focused on the areas of the brain near the damaged areas and on the corresponding areas in the right hemisphere, and also compared the obtained indicators with the control group.

In the areas near the damaged areas, the scientists noted increased activity in the theta and delta ranges (from 1 to 7 Hertz) and decreased activity in the beta and gamma ranges (from 15 to 50 Hertz), which was not observed in patients in the control group, and the severity of aphasia directly depended on the magnitude of abnormal activity. Since the lesions of the participants were different (both in size and in place in the left hemisphere), the researchers made a map of the localization of abnormal activity for each of them – and then used it for further stimulation.

Stimulation was carried out by micropolarization – changes in brain activity using transcranial direct current exposure. Depending on the type of anomaly, the stimulation was either anodic (activating) or cathodic (inhibiting): so scientists could increase weak activity in small ranges and reduce the activity of large ranges. In the control condition, empty stimulation was used.

After stimulation, the test of speech abilities was repeated. Scientists found that after anodic micropolarization, participants began to correctly name 61 percent more words than before stimulation, but improvement was observed only in the group that was given more difficult words. As for brain activity, with the help of anode stimulation, scientists managed to achieve an increase in activity in the gamma range (from 25 to 50 Hertz) near the stroke site and a decrease in activity in the theta range (from 4 to 7 Hertz) in the corresponding areas of the right hemisphere.

With high–quality and effective rehabilitation, the functions of speech areas damaged by stroke are taken over by other parts of the brain: either located nearby or located contralterally - in less active speech areas of the right hemisphere. The authors of the new work have shown that stimulation can speed up this process, and it is necessary to focus on restoring brain activity in intact areas – so it can be "tuned" to speech processing faster.

Stroke of the left hemisphere is not the only cause of possible aphasia: speech disorders can occur with tumors and even trauma. As in the case of stroke, the success of rehabilitation depends on the location of the affected area and the severity of the condition. At the same time, if the damage is received during intrauterine development, the speech functions of the left hemisphere will take over the corresponding areas of the right – and speech will remain intact.

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