‘White matter’ behaves differently in children with dyslexia

Trans-institutional neuroimaging research at Vanderbilt University finds that the brain may be structured differently in children with dyslexia, a reading disorder that affects up to 17 percent of the population.

The behavioral characteristics of dyslexia are well documented, including struggling to recognize and decode words as well as trouble with comprehension and reading aloud.

Laurie Cutting, Patricia and Rodes Hart Professor of Special Education, and professor of psychology and human development, radiology and pediatrics at Vanderbilt Peabody College of education and human development, is part of a transinstitutional team of researchers using neuroimaging to examine structural differences in connectivity in children with dyslexia as compared to typically developing readers.

Study results were recently published by journals Brain Connectivity and Brain Research.

While many dyslexia studies focus on the cerebral cortex, the researchers, which included faculty from pediatrics, engineering, radiology, psychology, special education and other Vanderbilt departments and centers, targeted the sub-cortical thalamus region. The thalamus serves as the brain’s connector—relaying sensory and motor signals back to the cerebral cortex via nerve fibers that are part of the brain’s “white matter.” The thalamus also regulates alertness, consciousness and sleep.

Evaluating 40 children ages 8 to 17 years, evenly divided between typically developing readers and those with developmental dyslexia, the researchers used diffusion tensor imaging to visually map the structure of the brain in an effort to better understand the role of the thalamus in reading behavior.

The data were collected at Johns Hopkins University School of Medicine’s Kennedy Krieger Institute and the Vanderbilt University Institute of Imaging Science (VUIIS) at Vanderbilt University Medical Center.

“A different pattern of thalamic connectivity was found in the dyslexic group in the sensorimotor and lateral prefrontal cortices,” Cutting said. “These results suggest that the thalamus may play a key role in reading behavior by mediating the functions of task-specific cortical regions. Such findings lay the foundation for future studies to investigate further neurobiological anomalies in the development of thalamo-cortical connectivity in individuals with dyslexia.”

In a related study, the team examined connectivity patterns in a cortical region known to be especially important for reading: the left occipito-temporal region, sometimes referred to as the visual word form area.

Brain activity in the thalamus (Vanderbilt) — Fiber pathways in the brain. (Vanderbilt)

While there have been many functional MRI studies examining this region, there is not a consensus on the region’s functionalities, and studies of the visual word form area‘s structural connectivity are relatively new.

Cutting and her colleagues used diffusion MRI to study the structural connectivity patterns in the left occipito-temporal region and surrounding areas of the brain in 55 children.

“Findings suggest that the architecture of the left occipito-temporal region connectivity is fundamentally different between children who are typically developing readers and those with dyslexia,” Cutting said.

The typically developing readers showed greater connectivity to linguistic regions than the dyslexic group. Those with dyslexia showed greater connectivity to visual and parahippocampal (memory encoding and retrieval) regions.

“Together these studies suggest anomalous patterns of subcortical and cortical connectivity that may underlie the functional abnormalities in the left occipito-temporal region in individuals with dyslexia,” Cutting said.

“This work also shows how collaborations between investigators with different expertise can lead to important discoveries and breakthroughs,” said John C. Gore, Hertha Ramsey Cress University Professor at Vanderbilt and director of VUIIS. “The interaction of developmental neuroscientists with imaging specialists was essential to produce these exciting results.”

This work was conducted in part using the resources of the Advanced Computing Center for Research and Education at Vanderbilt University (ACCRE).