Biological marker for dyslexia discovered by researchers

Learning to read is an essential part of educational development, but the process doesn’t always go smoothly for every child.

While it’s hard to know for certain, the National Institutes of Health estimates around 15 percent of the national population may have dyslexia, a developmental reading disorder characterized by difficulty reading and processing written language.  Those with dyslexia often have normal and above-average intelligence, making their condition completely unrelated to their intellect.

Many in the scientific community have theorized that a person’s biology is linked to the development of dyslexia, but the biological mechanisms have never been truly understood.  But now, researchers from Northwestern University in Evanston, Ill., have found a biological marker that could indicate when a person is struggling with reading comprehension.

According to lead author of the study Nina Kraus, Hugh Knowles Professor of Neurobiology, Physiology and Communication at Northwestern, the biological underpinnings all revolve around the brain and a seemingly unrelated action – a person’s hearing ability.

“The thinking is that when you’re learning to associate letters on a page with their meanings, you’re linking your auditory representation of these sounds -connecting what you know about how the sounds sound to the corresponding letters on the page,” Kraus told about their theory. “You’re thinking what you know about sounds and their corresponding representation.”

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To learn more about Kraus's research, visit the Auditory Neuroscience Laboratory.

Kraus and her colleagues studied 100 school-aged children with a wide range of reading abilities, using electrodes to measure their brain wave responses as they listened to and encoded speech sounds.

“Our biological approach is one that captures the response of the nervous system to sound,” Kraus told “If you put electrodes on people, the neurons in your brain that respond to sound are giving off electricity – and we can measure that electricity.”

According to Kraus, sound waves contain a lot of information that changes very rapidly – sometimes in fractions of nanoseconds.  Sound wave information includes everything from frequency and pitch to the harmonics of sound.  Through the use of their measuring technique, Kraus and her colleagues were able to see how sounds are represented by children’s brains.

Ultimately, they discovered the poorest readers in class were much more inconsistent in their sound encoding abilities, while the best readers in class encoded sounds with much more stability.  This lead the researchers to believe that sound encoding stabilizes as children become better readers and learn to better connect sounds with their intended meanings.

Kraus said this approach to understanding how children process sound is important, because children who are poor readers or have trouble encoding sound waves can end up poorly “train” their nervous systems over time.

“The language connections and peoples’ ability to remember sounds – because this is not developing accurately, then it has consequences for how the nervous system gets shaped or not with respect to its response for sound,” Kraus said.  “As you repeatedly make good sound to meaning connections, it tunes up your hearing so that your hearing system now automatically responds to sounds that have meaningful elements in them.”

Children can change their biology and train their brains to process sound more consistently.  In another study conducted by Northwestern’s Auditory Neuroscience Laboratory, Kraus and her colleagues gave assistive listening devices to children with reading impairments.  During class, their teacher would speak into a microphone, and her lectures were transmitted through the listening devices directly into the students’ ears.

A year later, the children showed significant improvements when it came to their reading abilities – as well as how their brains encoded sound.  Kraus said the device helped them learn to what sounds they need to pay attention, as well as to ignore distracting sounds – such as desks scraping or the sound of the air conditioner.

“Your nervous system learns; we are what we do,” Kraus said of the study. “If you go to the gym and work out your muscles, they may turn into something different, and your nervous system very much changes based on your experience with sound.”

Now knowing the biological underpinnings of dyslexia and reading impairment, Kraus hopes this technology can one day be used by teachers and scientists to better understand how the reading process develops in a child’s brain – and to ultimately help them become better readers if they start to fall behind.

“It’s one additional piece that informs them about the hearing health of an individual child,” Kraus said.