Dyslexia is the most prevalent of learning disabilities, affecting nearly 12 percent of Americans with reading disabilities and difficulties processing visual information.
For a long time, scientists felt that dyslexics had an altered capacity for vision in their brains. This would make sense, as learning disabilities, such as autism, are often caused by differences in brain chemistry and development.
A new study, however, suggests otherwise — at least in the case of dyslexia. Researchers at Georgetown University Medical Center (GUMC) used brain imaging to test the differences in brain function between dyslexic and non-dyslexic children. The children all held similar levels of intelligence, and the non-dyslexic children represented ideal reading levels.
In doing this, the researchers established the relationship between reading ability and brain activity in the visual portion of the brain during the perception of visual motion. For both dyslexics and non-dyslexics, there was more activity in that one region, whether or not they read well. While differences between dyslexics and controls based on age were established, the results failed to demonstrate differences for the reading levels based on brain activity. This suggested that an altered visual cortex function can represent a side effect, rather than a cause, of dyslexia and its effects on reading abilities.
The research team then studied younger children without dyslexia, comparing them to dyslexics on their reading level. These two groups also had similar levels of brain activity in visual regions. This indicates that the common reading issues amid dyslexics are not based in brain malfuncitons at all, but rather ability and whether or not they were taught to read effectively.
After comparison between the two groups indicated the same brain activity in visual regions, children with dyslexia received a reading intervention. Intensive tutoring was provided, addressing the core deficit in dyslexia, which is widely believed to be a weakness in the phonological component of language. The phonological compnonent of language that is lacking amid many dysliexics is, simply put, the ability to relate letters with sounds. As expected, the children made significant progress with their reading skills. In addition, activity in the visual system increased, suggesting it was mobilized by reading, but by no means exceeded the activity seen in control groups.
The researchers pointed out that these findings could have important implications for treatment. "Early identification and treatment of dyslexia should not revolve around these deficits in visual processing," said Olumide Olulade, Ph.D., the study's lead author and post-doctoral fellow at GUMC. "While our study showed that there is a strong correlation between people's reading ability and brain activity in the visual system, it does not mean that training the visual system will result in better reading. We think it is the other way around. Reading is a culturally imposed skill, and neuroscience research has shown that its acquisition results in a range of anatomical and functional changes in the brain."
While weakness of the brain's visual cortex is a hallmark of dyslexia, it is not the cause of the reading problems most dyslexics face. Secondly, the weaknesses in the visual cortex do not represent a symptom of dyslexia. They are not, as previous research assumed, an integral part of the way dyslexia alters people's ability to learn. Rather, it is a consequence of reading experience, or the lack of reading, itself.
This may suggest that parents with newly diagnosed dyslexic children should exhibit more patience while teaching children to read, or perhaps seek professional help in doing so.
Source: Olulade OA, Napoliello EM, Eden GM. Abnormal Visual Motion Processing is not a Cause of Dyslexia. Neuron. 2013.