Scientists Probe the Origins of Dyslexia12/21/11
WEDNESDAY, Dec. 21 (HealthDay News) -- Problems in how people
with dyslexia process the sounds they hear may be at the heart of
this learning disorder, new research suggests.
The study findings, published in the Dec. 22 issue of the
Neuron, may one day lead to better therapies for children and adults who are diagnosed with this common yet still ultimately mysterious condition.
And different people with dyslexia may have differences in
brain-processing patterns, which could help distinguish subtypes of
Dyslexia affects about 5 percent of school-aged children.
Although we "typically think of dyslexia as an impairment of
reading or the printed word, previous research has suggested that
there's an auditory-processing component. . . It's not just the
printed word but also auditory," said Dr. Andrew Adesman, who was
not involved with the study but is familiar with the findings.
Indeed, one of the biggest risk factors for dyslexia is delays
in spoken language in young children, said Adesman, chief of
developmental and behavioral pediatrics at the Steven &
Alexandra Cohen Children's Medical Center of New York, in New Hyde
Previous brain imaging studies had shown abnormal processing of
brief sounds in people with dyslexia, but it has been unclear what
the neurophysiological mechanism was behind the abnormalities,
according to study authors Katia Lehongre, from the Ecole Normale
Superieure in Paris, and colleagues.
The French authors focused on a phenomenon called "sampling,"
which refers to how the brain initially responds to sounds.
Specifically, sampling involves the processing of phonemes, which
are the basic elements of sound.
"They're looking at where and how sound is processed," Adesman explained.
What the investigators found in people with dyslexia, as
compared to people who did not have dyslexia (control-group
members), were abnormalities in the left auditory cortex of the
The brains of people with dyslexia may "overreact" to phonemes
at high-frequency rhythms. This could interfere with verbal memory
and, hence, speech, the study found.
"The left auditory cortex may be less responsive to certain sound frequencies that are optimal [for processing] phonemes," Adesman explained.
Although the research is "important," said Dr. Harold Levinson,
clinical/research director of the Levinson Medical Center for
Learning Disabilities in Great Neck, N.Y., it may not take into
account the complexity of dyslexia and the many brain processes
The particular brain abnormalities identified in this study may
just be a reflection of other problems in the cerebellum region of
the brain, he said.
A number of questions remained unanswered, Levinson added.
The U.S. National Library of Medicine has more on
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