The brain abnormalities that cause dyslexia may be deeper and more pervasive than previously thought, according to research from the Massachusetts Institute of Technology.
A study published Wednesday in the journal Neuron found that the brains of people with the reading disorder respond differently not just to words, but to objects and faces, as well.
The research suggests that the brain’s plasticity — its ability to change in response to experiences — is reduced in people with dyslexia, pointing to “the core biological difference in the brains of people with dyslexia,” said John Gabrieli, a professor of brain and cognitive sciences, a member of MIT’s McGovern Institute for Brain Research, and senior author of the study.
Dyslexia is a neurological disorder that, even in highly intelligent people, makes it difficult to learn how to read, because of problems connecting speech sounds with letters and words on the page.
The International Dyslexia Association estimates as many as 15 to 20 percent of the population may have symptoms of dyslexia, including slow or inaccurate reading, poor spelling, poor writing, or a tendency to confuse similar words.
The study offers no immediate help for people with dyslexia or those who teach them, but along with other research, it could someday lead to new treatments, including medications or methods to train the brain.
Guinevere Eden, director of the Center for the Study of Learning at Georgetown University Medical Center, who was not involved with the MIT study, said the findings open new avenues for research — but also highlight the difficulty of treating dyslexia.
“In the past, people have been very focused in areas known to be involved in reading,” she said. The MIT work suggests the root problem “is quite pervasive across the entire brain. . . .
“It speaks to the gravity of the disorder, and explains why it is such a terrible struggle for children and adults with dyslexia to learn,” said Eden, whose own research has focused on dyslexia. “Reading is a uniquely human skill, and it doesn’t come easy.”
In the MIT experiments, MRI machines scanned the brains of adults with dyslexia and those without the disorder while they undertook several tasks. They listened to a series of spoken words, and looked at written words, pictures of objects, and pictures of faces. Sometimes, the identical words or pictures were repeated over and over; other times the items varied.
In people without dyslexia, repetition led to brain changes. When presented with a new item, certain brain regions lit up on the MRI, indicating increased activity. But as the task was repeated, that activity dimmed.
“If something is seen over and over again, heard over and over again, physical changes in the brain make you more efficient,” Gabrieli said. This is called “neural adaptation” and is considered critical to learning.
But in people with dyslexia, neural adaptation was reduced. Their brains worked almost as hard absorbing material seen or heard repeatedly as they did when facing something new. Most strikingly, this effect was seen even in tasks unrelated to reading, suggesting that dyslexia affects many brain regions, not just those involved with language.
“That’s a surprise,” Gabrieli said, because dyslexic people typically have problems only with reading. “People with reading difficulty don’t have difficulty recognizing faces, tables, and chairs.”
He speculated that the brain has developed work-arounds for more ancient skills such as identifying faces and objects. “Our guess is that through evolution, we have other redundant capacities. If you can’t learn it one way, you learn it another,” he said.
But the brain did not evolve for reading, a capability developed only recently in human history. “Reading is so demanding, there may not be a good second or third way to accomplish the same thing,” Gabrieli said.
In a final experiment, the MIT group tested first- and second-graders and found the same differences in those with dyslexia.
In future research, Gabrieli hopes to discern whether the reduced plasticity also occurs with other senses in addition to hearing and seeing, and in younger children who have not started to read.
Dr. Albert M. Galaburda, a neurology professor at Harvard Medical School and codirector of the university’s Mind Brain Behavior Interfaculty Initiative, identified what he described as a weakness in the study. It failed, he said, to consider that the differences observed in the MRIs might indicate differences in the way the dyslexic brain receives input, rather than in its ability to adapt to that input.
For example, when a word is repeated, perhaps the person hearing it does not perceive it as identical to the word that preceded it, because of dyslexia-related interference in the brain. “The information is the same information when it comes into the brain but it’s handled differently,” he said. Studies have shown that people with dyslexia have trouble distinguishing between different voices, he said.
“I’m not saying they’re wrong,” Galaburda said, just that the study did not address that possibility.
Still, Galaburda welcomed the MIT study because it “agrees with a lot of people that think dyslexia is more than just a phonics problem, which has been the dogma in the field for a long time.
“We have a lot of children who get phonics through the nose and then don’t get better,” he said. “This kind of basic research opens new windows and allows people to think more broadly.”
This study and other research may lead to medications to treat dyslexia. But in the short term, Galaburda said, “We’re not going to be able to translate this quickly into some new treatment modality.”
The MIT research was paid for by the Ellison Medical Foundation, the National Institutes of Health, and a National Science Foundation Graduate Research Fellowship.