MIT neuroscientists have discovered a distinctive brain pattern that may explain why people with dyslexia have difficulty learning to read.
Researchers found that the brains of people with dyslexia have a diminished ability to adapt to repeated input — a trait also known as neural adaptation. In other words, when someone with dyslexia sees the same word repeatedly, the regions of the brain involved in reading do not show the same adaption as someone who does not have dyslexia. The brain’s plasticity, which helps it learn new things, is reduced.
“It’s a difference in the brain that’s not about reading per se, but it’s a difference in perceptual learning that’s pretty broad,” said the study’s senior author John Gabrieli, professor of brain and cognitive sciences and member of MIT’s McGovern Institute for Brain Research. “This is a path by which a brain difference could influence learning to read, which involves so many demands on plasticity.”
Using MRI scans, researchers asked a group of young adults with and without dyslexia to perform a variety of tasks. In the first experiment, the volunteers listened to a series of words read by either a single speaker or four different speakers.
There were distinctive patterns of activity in both groups of volunteers. In the group without dyslexia, the areas of the brain associated with language showed neural adaption after hearing words read by a single speaker, but not when the words were read by various speakers. In the dyslexic group, participants showed less adaptation to hearing words said by a single speaker.
“You learn something upon the initial presentation that makes you better able to do it the second time, and the ease is marked by reduced neural activity,” Gabrieli said. “Because you’ve done something before, it’s easier to do it again.”
The researchers then ran a similar series of experiments, but instead of listening to words, the volunteers were asked to look at pictures of the same word or different words; pictures of the same of different objects; and pictures of the same or different faces. In each experiment, the dyslexic participants’ brain regions that interpret words, objects and faces did not show neural adaptation when they were shown the image multiple times.
“The brain location changed depending on the nature of the content that was being perceived, but the reduced adaptation was consistent across very different domains,” Gabrieli said.
Gabrieli was surprised to find the widespread impact of dyslexia, even during tasks that had nothing to do with reading, such as recognizing faces or objects.
Finally, the researchers tested first and second graders with and without dyslexia, and found the same differences in neural adaptation as the adults.
Experts such as Guinevere Eden, a professor of pediatrics and director of the Center for the Study of Learning at Georgetown University Medical Center, say that these new findings are “groundbreaking.”
“For children with dyslexia, we know that the brain looks different in terms of anatomy and function, but we have not been able to establish why,” said Eden, who was not involved in the research. “This study makes an important step in that direction: It gets to the true characteristics of the properties of the neurons in these brain regions, not just their outward appearance.”
Nearly 10 percent of any given population has some degree of dyslexia — that’s more than 7 billion people worldwide, according to a report by Dyslexia International. But dyslexia should not be viewed as a lifelong crippling problem — many successful and brilliant people have battled dyslexia, from Albert Einstein to billionaire business magnate Richard Branson.