Dyslexia,
the most commonly diagnosed learning disability in the United States,
is a neurological reading disability that occurs when the regions of the
brain
that process written language don't function normally.
The use of non-invasive functional neuroimaging tools has helped
characterize how brain activity is disrupted in dyslexia. However, most
prior work has focused on only a small number of brain regions, leaving a
gap in our understanding of how multiple brain regions communicate with
one another through networks, called functional connectivity, in
persons with dyslexia.
This led neuroscience PhD student Emily Finn and her colleagues at
the Yale University School of Medicine to conduct a whole-brain
functional connectivity analysis of dyslexia using functional magnetic
resonance imaging (fMRI). They report their findings in the current
issue of 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 Finn.
In total, they recruited and scanned 75 children and 104 adults. Finn
and her colleagues then compared the whole-brain connectivity profiles
of the dyslexic readers to the non-impaired readers, which revealed
widespread differences.
Dyslexic readers 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
around the inferior frontal gyrus. This altered 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 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."
Additionally, 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 rather than transitioning to more automatic, visual-based
strategies for word recognition.
A better understanding of brain organization in dyslexia could
potentially lead to better interventions to help struggling readers.
Story Source:
The above story is based on
materials provided by
Elsevier.
Note: Materials may be edited for content and length.
Journal Reference:
- Emily S. Finn, Xilin Shen, John M. Holahan, Dustin Scheinost, Cheryl
Lacadie, Xenophon Papademetris, Sally E. Shaywitz, Bennett A. Shaywitz,
R. Todd Constable. Disruption of Functional Networks in Dyslexia: A Whole-Brain, Data-Driven Analysis of Connectivity. Biological Psychiatry, 2014; 76 (5): 397 DOI: 10.1016/j.biopsych.2013.08.031
Cite This Page:
Elsevier.
"Readers with dyslexia have disrupted network connections in the brain,
map the circuitry of dyslexia shows." ScienceDaily. ScienceDaily, 28
August 2014.
<www.sciencedaily.com/releases/2014/08/140828091245.htm>.