Transcranial direct current stimulation or tDCS is a non-invasive process that uses electricity to stimulate areas of the brain. Now, we know transcranial electrical stimulation has been a hot topic of controversy in the medical research community.
One team claimed that tDCS can cure depression. Another said that it can help patients with manic episodes. The only problem is – tDCS works, but the researchers aren’t completely sure how. In fact, research shows that transcranial direct current stimulation can reduce stuttering in adolescents and adults.
So, while we are aware of the controversies, let us simply state what new studies on the effects of transcranial direct stimulation on stuttering have found. Prof Kate Watkins, Principal Investigator and neuroscientist at the University of Oxford states, "Stuttering can have a detrimental effect on people's lives…tDCS is the future of stuttering treatment."
What's the Effect of tDCS on Stuttering in Adults?
Around 5% of all children and 1% of adults stutter. Early intervention can help children who stutter. Without speech therapy, children can go on stuttering into adulthood. Speech therapy for stuttering does work for adults. However, the results are not quick or long-lasting in adults as they are in children.
Although speech therapy has evolved since 1930, most popular therapy techniques still use intensive training, practice, and adopting "unnatural" sounding speech. Therefore, tDCS is a new ray of hope for adults who have been stuttering for years.
tDCS involves strapping electrodes on the temple and passing an almost undetectable direct current through the head. The study says that the current is mild enough so the people involved cannot tell when the electrodes are switched on or off.
Now, Watkins has been studying the effects of passing direct current via electrodes through the head. Her team had already linked stuttering to subtle differences in brain activity – more activity in the right hemisphere of the brain than usual. Watkins observed that tDCS could shift patterns of brain activity and reduce stuttering.
Study 1: tDCS and its long-term effects on stuttering in adults
Jennifer Chesters et al. conducted the first trial investigating whether tDCS can offer long-lasting positive effects on stuttering among PWS (People Who Stutter). The team predicted that applying (anodal) stimulation along with temporary fluency inducers (like the use of a metronome during speech production) could lead to longer-lasting fluency improvements in adults.
This particular study involved 30 male adults who stutter. The trial was double-blinded and completely randomized. As a part of this study, 15-randomly chosen participants (Group 1) received 1 mA of tDCS over their left frontal cortex for 20-minutes along with metronome-guided speech and reading practice (choral speech) for 5 consecutive days.
The other group (Group 2) of 15 adults who stutter received identical speech fluency intervention alongside a sham stimulation.
Speech fluency during reading was assessed before and after stimulation each day for 5-days. Next, the research team assessed speech fluency after 1-week and 6-weeks of the intervention.
The record shows that the anodal stimulation combined with traditional speech fluency intervention significantly reduced the percentage of disfluent speech measured after 1-week. At 6-weeks after the stimulation, Group 1 maintained the improvement during reading. However, fluency was absent during conversations.
The outcome scores measured according to the Stuttering Severity Instrument (Version 4) showed significant improvement at both 1-week and 6-weeks among participants of Group 1, but not Group 2.
The team led by Jennifer Chesters concluded that tDCS can improve fluency in adults when used in combination with direct behavioral interventions for stuttering.
Shortcomings of using tDCS with Choral Speech Technique
Still, one question remains, why did the study group perform well during reading tasks, but stutter during conversations? According to Jennifer Crinion, the study does not clearly state how long Chesters' team paired the anodal tDCS with the metronome conversation task. History shows that tDCS typically works well when paired with known or familiar tasks.
However, tDCS may not facilitate fluency during novel tasks such as speaking in front of an audience or holding a conversation. Crinion continues to state, "This may explain why Chesters et al. found differences between two tasks after 6-weeks."
tDCS can modulate the firing of neurons in the stimulated brain area. The process will only induce the firing of neurons that are already depolarized or near the threshold. Neurons that are not meant to be engaged in a task will not be influenced by tDCS.
Crinion has made this critical observation regarding the specificity of the tDCS intervention and the resulting reading fluency achieved by Group 1.
Study 2: Cathodal tDCS of Right Broca’s Area to Reduce Stuttering
A similar study was conducted by Yasuto Yada MS et al. However, in this study, the team focused on the activation of the right Broca’s area and Wernicke’s area using cathodal tDCS among PWS.
The team chooses adults who stutter as participants. As the PWS read their passages aloud, the team applied tDCS using electrodes. It included an anodal or cathodal electrode placed over one of the language areas and its homologous region in the right hemisphere and a second electrode placed on the contralateral supraorbital region.
Each participant received anodal and cathodal tDCS sessions. Each of these sessions included a sham simulation. The team then analysed the effects of simulation polarity and electrode location.
The results of the analyses showed a significant interaction between polarity and location, and the frequency of disfluencies. tDCS montage, including the cathodal electrode over the right Broca's area, reduced the frequency of stuttering among participants.
The tDCS induced a reduction of the over-activity of the right Broca's area and reduced stuttering severity.
Can tDCS become The Future of Stuttering Treatment?
The two contemporary studies involving tDCS as a non-invasive tool that can test the hypotheses researchers have gathered from functional imaging studies on subjects who stutter. The effect of the tDCS will depend upon the polarity of the electrodes.
We will need more longitudinal studies to understand or confirm whether tDCS can become standard treatment or cure for stuttering. However, the present evidence definitely gives us hope. For now, you can install Stamurai - the #1 speech therapy app for stuttering.
