Brain Imaging Shows Dyslexia Not A Matter Of IQ
September 29, 2011

Brain Imaging Shows Dyslexia Not A Matter Of IQ

Stanford University researchers have used an imaging technique to show that brain activation patterns in children with poor reading skills and a low IQ are similar to those in poor readers with average IQs, findings that have implications for the physiological basis of dyslexia.

Some 5 to 10 percent of American children are diagnosed as dyslexic, a brain-based learning disability that impairs a person's ability to read.

Schools and psychologists have historically relied upon a child's IQ to define and diagnose dyslexia: If a child's reading achievement was below expectation based on IQ, he would be considered dyslexic, while a poor reader with a low IQ would receive some other diagnosis.

However, the current findings provide "biological evidence that IQ should not be emphasized in the diagnosis of reading abilities," said Dr. Fumiko Hoeft at Stanford's Center for Interdisciplinary Brain Sciences Research, senior author of the study.

Indeed, the study provides more definitive evidence about poor readers having similar kinds of difficulties, regardless of their general cognitive ability.

“We found that children who are poor readers have the same brain difficulty in processing the sounds of language whether they have a high or low IQ,” said Massachusetts Institute of Technology neuroscientist John Gabrieli, who worked on the study.

“Reading difficulty is independent of other cognitive abilities,” he said.

The study involved 131 children 7 to 17 years of age.  According to a simple reading test and an IQ measure, each child was assigned to one of three groups–typical readers with typical IQs; poor readers with typical IQs; and poor readers with low IQs.  All were shown word pairs and asked whether they rhymed. Spellings didn´t indicate sound similarities.

Using functional magnetic resonance imaging, or fMRI, the researchers observed the activity in six brain regions important in connecting print and sound.

The researchers found that poor readers in both IQ groups showed significantly less brain activity in the observed areas compared with typical readers, and that there was no difference in the brains of the poor readers, regardless of their IQs.

“These findings suggest the specific reading problem is the same whether or not you have strong cognitive abilities across the board,” said Gabrieli.

The study could have an important impact on both the diagnosis and education of poor readers.

The revised definition of dyslexia proposed for the upcoming Diagnostic and Statistical Manual (DSM-V), psychiatry´s diagnostic bible, “currently lacks neurobiological evidence for the removal of ℠severe discrepancy´ [between IQ and reading ability],” said Hoeft.

“Our study will be the first to provide such evidence.”

The research could also change the ways educators help poor readers at all levels. 

Educators commonly offer reading- and language-focused interventions to bright dyslexics, to bring their reading up to the level of their expected achievement, while considering such specific remediation futile for less-“smart” children.

But if teachers understand that the same thing is going on in the brains of all poor readers, they may see that all those children could benefit from the same interventions, the researchers said.

The findings will be published in an upcoming issue of Psychological Science.


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