(Reuters Health) – Bumping up the power of certain brain waves in the left auditory cortex may help alleviate sound-processing deficits and improve reading accuracy in adults with dyslexia, a new study suggests.
Swiss researchers confirmed that people with dyslexia have altered low-gamma oscillatory function in the part of the brain that processes language phonemes, and that applying transcranial alternating current stimulation (tACS) in that area seems to temporarily ameliorate reading problems, according to the report published in PLOS Biology.
“The take-home message from our study is that very mild electrical stimulation delivered over the left auditory cortex at 30Hz, specifically improves phonemic processing and reading abilities in people with dyslexia,” said the study’s lead author, Silvia Marchesotti, a postdoctoral researcher at the University of Geneva.
“In doing so, we demonstrated the causal relationship between phonemic processing and brain oscillations around 30Hz, a fundamental point that was not previously fully established,” Marchesotti said in an email. “A previous study from our group has shown a deficit in the oscillations at 30Hz in the left auditory cortex of people with dyslexia. This frequency is particularly relevant as it is involved in the encoding of phonemes, the smallest units of language that our brain can process (for instance /b/ or /d/).”
Marchesotti and her colleagues suspected that if they could boost the power of 30Hz brainwaves with a noninvasive method, they might impact dyslexia deficits.
The researchers recruited 15 adults with dyslexia and 15 fluent readers. At the outset, the participants’ reading abilities were tested and their brain waves analyzed. As predicted, those with dyslexia had deficits in 30Hz brainwaves. To boost 30Hz power, the researchers would apply transcranial alternating current stimulation over the left auditory cortex. They ran their experiment multiple times, once in a sham condition, once with 30 Hz stimulation and once with 60 Hz stimulation.
“Transcranial alternating current stimulation (tACS) is a simple procedure consisting of placing a few electrodes on the scalp – in our case five electrodes – to deliver an alternating current at a specific frequency between the electrodes,” Marchesotti explained. “The current synchronizes the activity of the neurons in the auditory cortex, which we can measure as an enhancement of neural oscillation power at 30Hz using electroencephalography.”
After the 20 minutes of stimulation, the participants’ reading abilities were tested, and again one hour later.
The 30Hz stimulation improved reading accuracy in those with dyslexia but worsened the results with fluent readers. All participants read more slowly after the brain stimulation, and the researchers suspect that may be due to a “nonspecific tACS effect.”
Neither the 60Hz stimulation nor the sham condition led to any improvements in reading ability in any of the participants.
“The positive effect was present immediately after the stimulation but gone one hour after,” Marchesotti said. “We think that a chronic stimulation, that is 20 minutes each day for several days, could induce longer-term neural plasticity but this remains to be determined.”
David Schretlen isn’t convinced yet.
“It’s a small sample and the results could be a fluke,” said Schretlen, a professor and director of the division of medical psychology at Johns Hopkins University in Baltimore. “It really needs to be replicated.”
Further, Schretlen said, it would be more convincing if the researchers had also compared the impact of the 30Hz boost in those with dyslexia to a boost in people who did not have the condition but were poor readers. “Then you’d know whether this boosts the reading of people who have clinical dyslexia or people who do poorly on tests,” he said.
SOURCE: https://bit.ly/2FaV6ij PLoS Biology, online September 8, 2020.