About 10 percent of the U.S. population suffers from dyslexia, a
condition that makes learning to read difficult. Dyslexia is usually
diagnosed around second grade, but the results of a new study from MIT
could help identify those children before they even begin reading, so
they can be given extra help earlier.
The study, done with
researchers at Boston Children’s Hospital, found a correlation between
poor pre-reading skills in kindergartners and the size of a brain
structure that connects two language-processing areas.
Previous
studies have shown that in adults with poor reading skills, this
structure, known as the arcuate fasciculus, is smaller and less
organized than in adults who read normally. However, it was unknown if
these differences cause reading difficulties or result from lack of
reading experience.
“We were very interested in looking at
children prior to reading instruction and whether you would see these
kinds of differences,” says John Gabrieli, the Grover M. Hermann
Professor of Health Sciences and Technology, professor of brain and
cognitive sciences and a member of MIT’s McGovern Institute for Brain
Research.
Gabrieli and Nadine Gaab, an assistant professor of
pediatrics at Boston Children’s Hospital, are the senior authors of a
paper describing the results in the Aug. 14 issue of the Journal of Neuroscience. Lead authors of the paper are MIT postdocs Zeynep Saygin and Elizabeth Norton.
The path to reading
The new study is part of a
larger effort involving approximately 1,000 children at schools
throughout Massachusetts and Rhode Island. At the beginning of
kindergarten, children whose parents give permission to participate are
assessed for pre-reading skills, such as being able to put words
together from sounds.
“From that, we’re able to provide — at the
beginning of kindergarten — a snapshot of how that child’s pre-reading
abilities look relative to others in their classroom or other peers,
which is a real benefit to the child’s parents and teachers,” Norton
says.
The researchers then invite a subset of the children to come to MIT for brain imaging. The Journal of Neuroscience
study included 40 children who had their brains scanned using a
technique known as diffusion-weighted imaging, which is based on
magnetic resonance imaging (MRI).
This type of imaging reveals
the size and organization of the brain’s white matter — bundles of
nerves that carry information between brain regions. The researchers
focused on three white-matter tracts associated with reading skill, all
located on the left side of the brain: the arcuate fasciculus, the
inferior longitudinal fasciculus (ILF) and the superior longitudinal
fasciculus (SLF).
When comparing the brain scans and the results
of several different types of pre-reading tests, the researchers found a
correlation between the size and organization of the arcuate fasciculus
and performance on tests of phonological awareness — the ability to
identify and manipulate the sounds of language.
Phonological
awareness can be measured by testing how well children can segment
sounds, identify them in isolation, and rearrange them to make new
words. Strong phonological skills have previously been linked with ease
of learning to read. “The first step in reading is to match the printed
letters with the sounds of letters that you know exist in the world,”
Norton says.
The researchers also tested the children on two
other skills that have been shown to predict reading ability — rapid
naming, which is the ability to name a series of familiar objects as
quickly as you can, and the ability to name letters. They did not find
any correlation between these skills and the size or organization of the
white-matter structures scanned in this study.
Brian Wandell,
director of Stanford University’s Center for Cognitive and
Neurobiological Imaging, says the study is a valuable contribution to
efforts to find biological markers that a child is likely to need extra
help to learn to read.
“The work identifies a clear marker that
predicts reading, and the marker is present at a very young age. Their
results raise questions about the biological basis of the marker and
provides scientists with excellent new targets for study,” says Wandell,
who was not part of the research team.
Early intervention
The
left arcuate fasciculus connects Broca’s area, which is involved in
speech production, and Wernicke’s area, which is involved in
understanding written and spoken language. A larger and more organized
arcuate fasciculus could aid in communication between those two regions,
the researchers say.
Gabrieli points out that the structural
differences found in the study don’t necessarily reflect genetic
differences; environmental influences could also be involved. “At the
moment when the children arrive at kindergarten, which is approximately
when we scan them, we don’t know what factors lead to these brain
differences,” he says.
The researchers plan to follow three
waves of children as they progress to second grade and evaluate whether
the brain measures they have identified predict poor reading skills.
“We
don’t know yet how it plays out over time, and that’s the big question:
Can we, through a combination of behavioral and brain measures, get a
lot more accurate at seeing who will become a dyslexic child, with the
hope that that would motivate aggressive interventions that would help
these children right from the start, instead of waiting for them to
fail?” Gabrieli says.
For at least some dyslexic children,
offering extra training in phonological skills can help them improve
their reading skills later on, studies have shown.
The research
was funded by the National Institutes of Health, the Poitras Center for
Affective Disorders Research, the Ellison Medical Foundation and the
Halis Family Foundation.
Fonte: http://web.mit.edu/newsoffice/2013/brain-scans-may-help-diagnose-dyslexia-0813.html
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