Dyslexic Patients Shown to Have Disordered Network Connections in the Brain

Scientists conducted a whole-brain functional connectivity analysis of dyslexia using functional magnetic resonance imaging (fMRI), and revealed how brain activity is disordered in dyslexic patients.

Dyslexia 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 tools has helped to characterize how brain activity is disrupted in dyslexia. However, most of the earlier research has focused on only a small number of brain regions, leaving a gap in the understanding of how multiple brain regions communicate with one another through networks, called functional connectivity, in individuals with dyslexia.

This led neuroscience PhD student Emily Finn and colleagues from the Yale University School of Medicine (New Haven, CT, USA) to conduct a whole-brain functional connectivity analysis of dyslexia using functional magnetic resonance imaging (fMRI) scanning. They reported their findings in the 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.

In total, the investigators recruited 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 demonstrated widespread disparities. Dyslexic readers’ brains showed 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 surrounding the inferior frontal gyrus. This changed connectivity profile is consistent with dyslexia-related reading problems.

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” tactics into adulthood rather than transitioning to more automatic, visual-based strategies for word recognition.

A better determination of brain organization in dyslexia could potentially lead to better interventions to help struggling readers, according to the investigators.

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Yale University School of Medicine