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A new study found no evidence that dyslexia is caused by having less brain tissue.

Previous studies suggest that dyslexics suffer reading disabilities because they have less gray matter in the brain. However, new research suggests that less gray matter may be a consequence of poorer reading experiences.

Researchers at Georgetown University Medical Center compared a group of dyslexic children with an age-matched group and a group of younger children who were matched at the same reading level as children in the dyslexia group.

"This kind of approach allows us to control for both age as well as reading experience," researcher Guinevere Eden, a neuroscientist and professor of pediatrics at GUMC, explained in a news release. "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."

The findings revealed that children in the dyslexic group showed less gray matter than those in the control group matched by age. However, this was not true when compared to the control group matched by reading ability.

Researchers said the findings suggest that anatomical differences seen the left hemisphere language processing regions are caused by reading experience and not dyslexia.

"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," lead author Anthony Krafnick, PhD., said in a statement.

Researchers said the latest findings also highlight the differences between changes in the brain caused by experience and those caused by cognitive impairment. Previous studies found that illiterate people who obtain reading skills as adults experience growth in brain matter. Researchers said that similar learning-induced changes in normal readers might result in differences between them and their dyslexic peers, who have not been able to have the same reading experiences and as a consequence have not experienced similar changes in brain anatomy.

The findings are published in The Journal of Neuroscience.