Experience, Not Genes, May Form Dyslexics’ Grey Matter
Many dyslexics weren’t born with less grey matter, according to a surprising recent study. Dyslexics’ grey matter may have developed less because they read less. The study contributes to the neuroscience community’s understanding of dyslexia—and may lead dyslexics to read more, despite feeling discouraged.
“There has been much interest,” Georgetown University Center for the Study of Learning Director Gueneviere Eden tells Bioscience Technology. Eden was senior author on the study, which found that reading experience, not genes, may dictate the volume of the brain’s (neuron-rich) grey area.
“I'm delighted to see the result, which makes absolute sense,” confirms Cathy Price via email. Price, a University College of London cognitive neuroscientist, was not involved in the study, but has written seminal papers in the area. “It was an essential study that needed to be conducted to avoid false impressions that reduced grey matter in dyslexics was the cause of reading problems (as opposed to the consequence of reading problems). Congratulations to the authors for setting this straight.”
The finding was initially unexpected, even though Eden’s study from the start was a bit different. Most studies comparing controls to dyslexics keep ages the same in both groups. Eden’s group decided to analyze brain MRI’s of two control groups. One of the control groups was comprised of “normal” readers who were the same age as the dyslexics. The other control group was comprised of “normal” readers who were younger, but who read at the same levels as the dyslexics.
“Going into the study, we fully expected to show that the differences in brain anatomy in the dyslexics would be observed when compared to both control groups, those matched on age and those matched on reading level,” Eden says. “This was because the reported differences in brain anatomy have been localized to brain areas involved in language - this is consistent with theories that dyslexia is a language-based learning disability. It seemed like a 'safe' project for my graduate student in neuroscience (Anthony Krafnick) and a way to fortify these already existing studies.”
But Krafnick found that reading experience dictated grey matter volume.
“Our results came as a surprise,” Eden says. “But then we recognized that there is a body of research that explains our findings. As discussed in the paper, it has been shown that when adult illiterates learn to read, and are compared to adult illiterates who did not have the opportunity to learn to read, there are profound differences in gray matter between these two groups—showing that learning to read (as an adult) increases brain tissue.”
A key former study in this area, Eden notes, was conducted by the above-mentioned Price. She found that illiterate Columbian guerillas were able to increase volume in both the grey and white matter of their brains as they learned to read.
Continues Eden: “Learning-induced increase in gray matter have been shown for a wide range of skills, from studying for college exams, to learning how to juggle balls.”
In the latter, classic Nature MRI study, Arne May of the University Medical Center of Hamburg-Eppendorf, found that the grey matter of adults temporarily increased during their training for juggling. Areas affected were associated with the processing and storage of complex visual motion. (After three months of juggling abstinence, the areas did shrink from disuse, however.)
“As such,” says Eden, “it makes sense that typically reading children are experiencing reading-induced brain matter increases, and these types of increases are likely to be reduced in the children with dyslexia who read poorly and, most likely, engage in reading less frequently.”
It has long been assumed that being born with less gray matter volume partially explains why dyslexics find it difficult to accurately, and rapidly, associate words sounds with their written counterparts. Eden’s study, in comparing dyslexic children with two different groups, let her group control for both age and reading experience. Differences in dyslexics' brain anatomy in comparison with both control groups would have suggested less gray matter leads to reading deficits. Instead, as noted, while the dyslexic group showed less gray matter compared with the age-matched control group, this was not true when compared with a control group matched by reading level.
This suggests reported differences in left hemisphere language processing areas are a result of reading experience, and are not a cause of dyslexia. It may impact interpretations of many prior dyslexia studies.
Says Eden: "I think there are many reasons why people with dyslexia need to be encouraged to continue to read. While there clearly is a biological reason for their struggles, with the right support from family members and professionals--who can provide the needed motivation and instructions--combined with a lot of hard work, the reading problems can be surmounted."
As a result of her study, on the other hand, it now appears true that "perhaps some of the brain-based differences are not as profound as we previously had assumed. This should not make us think lightly of the reading disability. It can be a devastating experience when a child discovers they do not have access to a skill that apparently comes to their peers easily and is the key to academic success."
But clearly the dyslexic brain is more "plastic" than believed--even among adults, she notes. "Our study in Neuron in 2004 showed the neural correlates of successful reading intervention in adults with dyslexia (using functional MRI). It demonstrated we must not give up on adults with dyslexia. They too can make significant improvements. It is never too late."
Price's response is equally emphatic, when asked if the new results mean dyslexics should keep reading.