January 15, 2014
Study Finds Less Gray Matter In Brain Not The Blame For Dyslexia
April Flowers for redOrbit.com - Your Universe Online
Research has found a link between reading disabilities and less gray matter in the brain for people with dyslexia. However, new evidence from Georgetown University Medical Center's Center for the Study of Learning suggests that this is a consequence of poorer reading experiences and not the root cause of the disorder.
Prior to this research, scientists assumed that the difference in the amount of gray matter might, in part, explain why dyslexic children have difficulties correctly and fluently mapping the sounds in words to their written counterparts during reading. The new findings, published in The Journal of Neuroscience, have turned this assumption of causality on its head.
The researchers compared two control groups with a group of dyslexic children. One of the control groups was an age-matched group included in most previous studies, while the other was a group of younger children who were matched at the same reading level as the children with dyslexia.
"This kind of approach allows us to control for both age as well as reading experience," explains neuroscientist Guinevere Eden, DPhil, a professor of pediatrics at GUMC. "If the differences in brain anatomy in dyslexia were seen in comparison with both control groups, it would have suggested that reduced gray matter reflects an underlying cause of the reading deficit. But that's not what we observed."
When matched by age with the control group, the dyslexic group showed less gray matter. This is consistent with previous findings. These results are not replicated when the dyslexic children were matched with younger children at the same reading level.
"This suggests that the anatomical differences reported in left hemisphere language processing regions appear to be a consequence of reading experience as opposed to a cause of dyslexia," says Anthony Krafnick, PhD. "These results have an impact on how we interpret the previous anatomical literature on dyslexia and it suggests the use of anatomical MRI would not be a suitable way to identify children with dyslexia," he says.
The researchers say that their work helps to determine the fine line between experience-induced changes in the brain and differences that are the cause of cognitive impairment. Prior studies have shown that illiterate adults gaining reading skills induces growth of brain matter. Discrepancies have been noticed between dyslexic people and their typical reading peers who undergo similar learning-induced changes. The dyslexic people have not enjoyed the same reading experiences and thus have not undergone similar changes in brain structure.