Their tongues might trip up over the name of the treatment, but people who stutter perform better on a speech test after receiving a daily jolt of transcranial direct current stimulation (tDCS).
That’s according to the results of a British trial, which found that coupling brain zapping with a five-day course of speech therapy helps those with stutters make positive, lasting changes in their communication skills.
Hobbyists and athletes are already using tDCS to boost their memory, learning, and creativity. And there’s a growing body of evidence that the neurostimulation can ease the symptoms of pain and depression, as well as promote recovery in stroke victims, including in their language skills.
But the new report, which will appear in the April 2018 issue of the journal Brain, is the first from a randomized clinical trial—the gold standard in medical research—to show that the technique can improve speech fluency in people who have not suffered any major insult to the brain but instead have a developmental speech condition.
“It’s a big deal,” says Rick Arenas, a speech scientist who runs the University of New Mexico Stuttering Lab and was not involved in the study. Neurostimulation, he says, “really looks extremely promising.”
Why it’s helping, however, remains unclear. It’s thought that the tDCS augments the brain’s ability to reorganize itself, thereby strengthening the new neural connections formed during behavioral speech therapy. But as Elizabeth Galletta, a speech-language pathologist at NYU Langone’s Rusk Rehabilitation, readily admits: “It’s still a black box.”
For the study, Jen Chesters, a speech and language therapist at the University of Oxford, worked with 30 stuttering speakers, spending five straight days training the men to read aloud and converse at a normal pace. (All were male to reduce variability between subjects.) During each day’s 20-minute therapy session, the participants all wore electrical caps on their heads, but only half actually received tDCS; the others received only sham stimulation—a brief buzz to trick people into thinking they were getting the real deal—and neither Chesters nor the participants knew who was getting what.
The tDCS device delivered a weak electric current through a credit card–sized electrode to the brain’s left frontal cortex, the key region for speech planning and production. The stimulation involved a constant current of just 1 milliamp—less than what’s needed to power a typical LED. Yet, that tiny tingle made all the difference.
Participants who received the tDCS showed significant reductions in their stuttering severity, both one week and six weeks after the intervention, whereas those who got the sham treatment experienced little to no change. “The tDCS is working to boost the effects of the behavioral intervention,” Chesters says.
That electric boost only helped modify certain measures of stuttering, though. It had lasting effects on participants’ abilities to declaim a written passage, but the increased conversational fluency that the men experienced one week after the intervention disappeared by week six. Outward improvements in speech smoothness also didn’t translate into improvements in the psychosocial aspects of stuttering, as measured by a self-assessment tool of participants’ own experiences.
So, while Galletta describes the Oxford team’s results as “very exciting,” she also thinks that tDCS researchers “need to look at stuttering in a more holistic way.”
Looking ahead, Chesters and her Oxford colleagues, led by neuropsychologist Kate Watkins, are planning to gather a wide range of metrics in their next study, a 40-person follow-up called INSTEP that is currently open for enrollment. In that trial, the researchers are pairing a 20-minute stimulation protocol in speech regions from both halves of the brain with a 40-minute speech-training paradigm (to be closer to a true clinical session), and then testing participants 12 weeks out from their weeklong intervention to see how long the benefits persist.
Meanwhile, across the pond at the University of Michigan in Ann Arbor, speech neurophysiologist Soo-Eun Chang and her colleagues are running their own tDCS trial for stuttering, but it differs from the Oxford group’s INSTEP study in a number of ways. It’s using high-definition tDCS, with electrodes smaller than a dime, to deliver 1.5 milliAmps of localized stimulation to a region in the brain involved in speech timing called the supplementary motor area.
Chang and her team are also putting study subjects in a brain scanner, applying functional magnetic resonance imaging before the intervention, right afterwards, and then at two later follow-up times. “The whole point is to see if we can increase their fluency level,” says Chang. “But on top of that, we are aiming to increase brain connectivity patterns with tDCS that may help sustain fluent speech for longer periods."
Given the ease with which amateur enthusiasts can now build their own tDCS rigs, there may be a temptation among people who stutter to shoot currents through their own heads as they engage in their fluency homework—but Arenas, who himself talks with a stutter and has tried tDCS for his own speech impediment, cautions against doing so. “This is extremely early on,” he says, “and there’s still a lot of work that should be done.”
Among the variables to be tested: where to place the electrodes, how much current to use, how long to deliver stimulation, and what kinds of behavioral tasks best pair with tDCS. “A lot of methodological research will be necessary to find out what the optimal parameters are, because there are a lot of choices you can make,” says Dirk den Ouden, a neurolinguist at the University of South Carolina.
Peggy Conner, a speech-language pathologist from CUNY’s Lehman College, has another concern about the technology. As she and other experts hone in on the optimal way deliver tDCS for persistent stutterers, there’s a risk that they may inadvertently further medicalize and stigmatize a condition that many think should instead be embraced as part of the normal neurodevelopmental spectrum.
“The danger of the pursuit of fluency for people who stutter,” Conner says, “is we may mitigate a greater societal need for stuttering acceptance.”
Elie Dolgin is a science writer specializing in biomedical research and drug discovery. After a PhD spent studying the population genetics of nematodes, he swapped worms for words—entering journalism as an editor at The Scientist, Nature Medicine, and STAT. Now a freelancer, Elie is a frequent contributor to New Scientist, Nature, IEEE Spectrum, and more.