fMRI and Circuitry Mapping Shows Dyslexic Readers Have Disrupted Brain Network

Dyslexia, the most typically diagnosed learning disability in the United States, is a neurologic reading disability that occurs when the regions of the brain that process written language do not function normally. The use of noninvasive functional neuroimaging approaches has helped characterize how brain activity is disrupted in dyslexic individuals.

However, most of the earlier research has centered on only a small number of brain regions, leaving a gap in the determination of how multiple brain areas communicate with one another through networks, called functional connectivity, in individuals with dyslexia. Scientists have now conducted a whole-brain functional connectivity analysis of dyslexia using functional magnetic resonance imaging (fMRI).

This led neuroscience PhD student Emily Finn and her colleagues from the Yale University School of Medicine (New Haven, CT, USA) to perform a whole-brain functional connectivity analysis of dyslexia using fMRI. They reported their findings September 1, 2014, issue of the journal Biological Psychiatry. “In this study, we compared fMRI scans from a large number of both children and young adults with dyslexia to scans of typical readers in the same age groups. Rather than activity in isolated brain regions, we looked at functional connectivity, or coordinated fluctuations between pairs of brain regions over time,” explained Ms. Finn.

The investigators enrolled and scanned 75 children and 104 adults. Ms. Finn and her colleagues then compared the whole-brain connectivity profiles of the dyslexic readers to the non-impaired readers, which showed widespread disparities. Dyslexic readers demonstrated decreased connectivity within the visual pathway as well as between visual and prefrontal regions, increased right-hemisphere connectivity, reduced connectivity in the visual word-form area, and persistent connectivity to anterior language regions around the inferior frontal gyrus. This shifted connectivity profile is consistent with dyslexia-related reading difficulties.

Dr. John Krystal, editor of Biological Psychiatry, said, “This study elegantly illustrates the value of functional imaging to map circuits underlying problems with cognition and perception, in this case, dyslexia.”

“As far as we know, this is one of the first studies of dyslexia to examine differences in functional connectivity across the whole brain, shedding light on the brain networks that crucially support the complex task of reading,” added Ms. Finn. “Compared to typical readers, dyslexic readers had weaker connections between areas that process visual information and areas that control attention, suggesting that individuals with dyslexia are less able to focus on printed words.”

Furthermore, young-adult dyslexic readers maintained high connectivity to brain regions involved in phonology, suggesting that they continue to rely on effortful “sounding out” strategies into adulthood instead of shifting to more automatic, visual-based approaches for word recognition.

A better understanding of brain organization in dyslexia could possibly lead to enhanced interventions to help struggling readers, according to the investigators.

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Yale University School of Medicine