Dyslexia Linked to Brain’s Inconsistency with Encoding Sound

Researchers from Northwestern University report that they have found a biological mechanism that appears to play a vital role in learning to read.

This finding provides significant clues into the workings behind dyslexia — a collection of impairments unrelated to intelligence, hearing or vision that makes learning to read a struggle. As many as one in 10 children is estimated to suffer from this disorder.

“We discovered a systematic relationship between reading ability and the consistency with which the brain encodes sounds,” said Nina Kraus, Hugh Knowles Professor of Neurobiology, Physiology and Communication.

The report, titled “Unstable Representation of Sound: A Biological Marker of Dyslexia,” is published in the Journal of Neuroscience.

For the study, researchers recorded the automatic brain wave responses of 100 school-aged children to speech sounds.  They discovered that the very best readers encoded the sound most consistently while the poorest readers encoded it with the most difficulty. The brain’s response to sound appears to stabilize as children learn to successfully connect sounds with their meanings.

On a positive note, biology is not destiny. In a previous study, the researchers found that the inconsistency with which the poorest readers encoded sound could be “fixed” through training.

In that study, children with reading difficulties were fitted for a year with assistive listening devices that transmitted their teacher’s voice directly into their ears. After a year, the children made improvements in reading as well as in the consistency with which their brains encoded speech sounds, especially consonants.

“Use of the devices focused youngsters’ brains on the “meaningful” sounds coming from their teacher, diminishing other, extraneous distractions,” said Kraus.

“After a year of use, the students had honed their auditory systems and no longer required the assistive devices to keep their reading and encoding advantage.”

According to Kraus, people rarely have difficulty encoding vowel sounds, which are relatively simple and long. It is consonant sounds, which are shorter and more acoustically complex, that are more likely to be incorrectly processed by the brain.

“Understanding the biological mechanisms of reading puts us in a better position to both understand how normal reading works and to ameliorate it where it goes awry,” says Kraus.

“Our results suggest that good readers profit from a stable neural representation of sound, and that children with inconsistent neural responses are likely at a disadvantage when learning to read,” Kraus adds.

“The good news is that response consistency can be improved with auditory training.”

Source:  Northwestern University