Can weak electrical current applied to the skull boost recovery from aphasia?

When people lose their ability to communicate due to brain damage caused by stroke or trauma, as persons with aphasia do, there is a good news and a bad news. The good news is that often not all is lost. Depending on the extensiveness of the damage, parts of the brain that used to be involved in speaking or understanding language may still be functioning. Speech therapies aim to induce these preserved areas to reorganize and regain their ability to produce and process speech. The not so good news is that such reorganization takes a long time, especially in older individuals.

Many people are familiar with traditional speech therapies that employ exercises to help persons with aphasia re-learn how to use language to communicate with their families and friends. Depending on the size and the location of brain damage, speech therapies can take years and improvement is usually slow. However, scientists are now looking into a newer type of treatment that combines traditional speech therapy with a weak electrical stimulation of the brain that might speed up recovery from aphasia. The method is called transcranial direct current stimulation (tDCS) and is applied non-invasively, by placing an electrode on top of the skull.

When people hear about electrical stimulation used to treat brain disorders, many conjure up an image from the 1975 movie “One flew over the cuckoo’s nest” which featured scenes of painful electroconvulsive therapy. This type of intervention, which in reality is painless, is still applied as a last resort to alleviate treatment-resistent depression and involves much stronger electrical currents than tDCS, which uses electrical current equivalent roughly to a 9V battery. The PBS Newshour video below describes the principles behind tDCS and how it could be applied for purposes like focusing the mind and keeping it alert.

The idea behind using tDCS in Aphasia therapy is that the small amount of current applied to the brain may enhance plasticity and prime the brain to learn faster. The approach would be to employ tDCS in combination with traditional clinical therapies rather than as a substitution.

There are many parts of the brain that are involved in understanding or producing speech and those parts are intricately connected into complex networks. Information flows between the various parts of the speech and language networks along cables called axons. Such information flow is important for the brain to access vocabulary and grammar rules, assemble words into sentences and send commands to the mouth and the tongue to produce speech. When stroke or trauma damages the areas that are part of this language network, the information flow is disturbed or cut off and people experience communication deficits. New connections need to be established between the preserved brain areas in order to regain one’s ability to speak.

The weak electrical currents of tDCS might stimulate the brain to form these new connections faster than it would with traditional speech therapy alone. But how exactly that would happen and what biological changes in the brain accompany the behavioral modulations observed in the video above is still unclear.

At present, tDCS as applied to aphasia is still considered experimental treatment and health insurance would not cover the cost of therapy. Data on tDCS efficacy for treating aphasia are still scarce. Most studies are conducted with small number of patients, limited language tasks, and short follow-up periods. However, at least some of the studies seem to suggest that tDCS has potential to improve aphasia rehabilitation.

Multiple centers in the United States, Canada, and Europe are in the process of conducting more rigorous clinical trials and may have more evidence soon whether tDCS works for aphasia. Those interested in enrolling in such studies can go to ClinicalTrials.gov to find out more information.

As methods improve and more data become available, tDCS may prove to be a great tool that will boost recovery from aphasia, which for the moment is still a long and arduous journey.

Norma