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Arnold School of Public Health

Clinical trial led by University of South Carolina researchers finds electrical stimulation can improve speech production among stroke survivors by 70 percent

August 31, 2018 | Erin Bluvas,

In a clinical trial led by University of South Carolina communication sciences and disorders professor Julius Fridriksson, researchers found that post-stroke aphasia patients who received transcranial direct current stimulation (tDCS) saw a 70 percent improvement in their ability to name common objects, a typical outcome measure used to assess speech production ability, compared to participants who did not receive tDCS. The study, which was the first large randomized controlled trial to examine the effect of tDCS on aphasia, observed that patients who received tDCS combined with speech therapy increased their correct object naming by 13.9 words while participants who received sham (placebo) tDCS combined with speech therapy increased their correct object naming by 8.2 words. 

“At six months following treatment completion, the improvement associated with the aphasia treatment was more than doubled for the patients who received electrical stimulation compared to those who received the placebo stimulation,” says Fridriksson. “If this effect is supported by future research, it could mean a major change in how rehabilitation of stroke is administered.”

Aphasia, a communication disorder resulting from stroke or injury to the brain that impacts patients’ ability to speak, listen, read and/or write but does not affect intelligence, is present in approximately 30 percent of all cases of stroke. Experts estimate that two million people in the United States are living with chronic aphasia.

Previous research suggests that behavioral treatment (i.e., speech therapy) is effective in improving communication and quality of life among individuals with long-term aphasia. However, recovery is often minimal, even with therapy.

tDCS offers a noninvasive method for treating aphasia, using an electrical current that enhances cortical activity, thereby modifying the function of distributed brain networks. Compared to drug treatment options, this approach reduces the toxicity that would otherwise affect trillions of cells outside the brain. Previous studies, including Fridriksson’s pilot studies dating back to 2008, have shown promise for the positive effects of tDCS on aphasia; however, these studies examined small sample sizes or single cases.

The present study, which was conducted in Fridriksson’s Aphasia Laboratory at the Arnold School of Public Health with a secondary site at the Medical University of South Carolina, tested this approach using a double-blind clinical trial over five years. With funding from the National Institute on Deafness and Other Communication Disorders, 74 individuals with post-stroke aphasia participated in three-week treatment sessions and six months of follow up assessments between August 2012 and March 2017.

The two groups (those who received the tDCS treatment and those who received a placebo simulation of tDCS) were well matched in terms of demographics and baseline aphasia scores. Ages ranged from 25 to 80 years with an average age of 60. Seventy percent of the participants were men, and 84 percent were non-Hispanic white. Many types of aphasia were present, with Broca aphasia as the most common. The participants all had moderate cases of aphasia (not too mild, not too severe) as a result of a single stroke in the left hemisphere of the brain more than six months prior to joining the study.

Treatment consisted of 15 one-on-one, 45-minute speech therapy sessions for both groups. During the first 20 minutes of each session, participants wore caps that either served as conduits for the tDCS treatment or provided an identical experience (i.e., tingling for the first 15-20 seconds followed by no detectable stimulation from the cap) that did not deliver tDCS during the sham condition. Consistent with double-blind trials, neither the researchers nor the participants knew which patients received tDCS and which patients received a simulation of tDCS.

At intervals up to 24 weeks post treatment, the researchers tested each patient’s ability to name different objects shown on a computer screen. Anomia, which is an aphasia patient’s inability to recall the names of everyday objects, is present in all types of aphasia regardless of severity.

“Because anomia is often the underlying factor affecting other aspects of aphasia and their associated adverse impacts on quality of life, naming is commonly targeted in aphasia treatment to improve both word retrieval and speech production,” Fridriksson explains.

Fridriksson and his team published one of their first paper on the study’s findings in the Journal of the American Medical Association (JAMA) Neurology on August 20. In an accompanying editorial by renowned neural repair expert Steve Cramer, the author considers what these gains may mean for patients who receive tDCS treatment.

“What does the ability to name 13.9 more objects mean in real life?” he wrote. “If you are trying to order lunch or select a grandchild’s birthday present, it can mean the world. If you are litigating a criminal case, it is likely insufficient.”

Through further research, Cramer suggests that these findings can be adjusted to optimize outcomes for aphasia patients: “Over time, identification of the ideal therapy intensity and duration, as well as target population, offers hope that language function can be substantially improved in individuals with post-stroke aphasia”.

In another recent paper, published in Brain Stimulation, the researchers share findings related to outcome variations based on genotypes (the first known study to do so), which lend additional insight into which patients may benefit most from tDCS. They found differences at both the outset of the study as well in their treatment outcomes in individuals with typical vs atypical brain-derived neurotrophic factor gene.

“This particular gene, known as the BDNF gene, influences neuroplasticity and appears to determine a person’s response to electrical brain stimulation and rehabilitation,” says Fridriksson. “We found that individuals with typical BDNF genotype tended to have milder symptoms in the first place, and those who received the tDCS treatment demonstrated more improvement. These results suggest that individuals with a certain genotype are more likely to benefit from tDCS during aphasia treatment.”

In an upcoming paper, also in Brain Stimulation, the authors discuss the merits of the study further. They emphasize that the results are reported as an average and focus on differences between experimental and control conditions using tDCS and speech therapy. In other words, the actual effects of the treatment ranged from small to medium in isolation, but combining tDCS and speech therapy with other forms of aphasia treatment could considerably enhance patient outcomes.

Thus, despite the researchers’ promising results, they urge that further trials be conducted to verify their findings and to identify other crucial aspects of treatment. Learning more about the effects of electrode placement, optimal dosage, tDCS targets, genotypes, and many other factors will bring researchers closer to customizing treatment plans for individuals with post-stroke aphasia.  


COMD’s Julius Fridriksson receives 2017 Breakthrough Leadership in Research Award

Public health researcher Julius Fridriksson helps stroke victims recover their words

Study provides empirical evidence for a dual route system in the brain that supports human speech processing, unlocking the door to future research to improve communication for stroke survivors

COMD’s Julius Fridriksson wins $11.1 million grant from NIH to create the Center for the Study of Aphasia Recovery

Julius Fridriksson named S.C. SmartState Endowed Chair of Memory and Brain Function

Brains on the brain (feature by UofSC Today)


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