Brain abnormality linked
to dyslexia
BY KATHLEEN O'TOOLE
Researchers at Stanford
have for the first time found clear evidence that some
reading problems are tied to a specific defect in neuron
function, according to a report published in the February
issue of the journal Neuron.
"We found that adults
with reading deficits have an abnormality in white matter
of the brain, which is vital for transmitting information
between the brain areas involved in language
comprehension," said psychology Professor John
Gabrieli, who was the senior researcher on the study
team.
The white matter
abnormality may indicate that the neuron's myelin is
defective, he said. A neuron sends vital messages in the
brain by transmitting electrical signals along an
extended appendage called an axon. The axon often is
covered with an insulating fatty sheath, known as myelin,
that speeds up the transmission of the signals. Myelin is
a major constituent of white matter.
In the study, the
researchers examined the brains of six adults with a
history of dyslexia and 11 adults who had no history of
reading difficulties using a new technique involving
magnetic resonance imaging. The scanner gauged the
cellular structure of the white matter by measuring the
microscopic movement of water molecules in the brain.
Abnormal water movement indicated faulty white matter,
Gabrieli said.
The researchers found that
the dyslexic group had poor functioning white matter that
may therefore slow message transmission in the regions
that are thought to connect the language processing areas
of the temporal and frontal lobes of the brain.
"We also found that
the level of reading performance of the dyslexic group,
as well as the healthy group, related to white matter
function," Gabrieli said. In the dyslexic group the
poorest readers had the poorest functioning white matter,
and in the healthy group the poorest readers had the
poorest functioning white matter.
The researchers hope that
in the future physicians will be able to use the
noninvasive imaging technique to identify children at
risk for reading impairments so that they can benefit
from early intervention.
The lead author of the Neuron
article is Torkel Klingberg, a former Stanford
postdoctoral researcher in Gabrieli's neuroscience lab
who is now in the Department of Neuroscience at
Karolinska Institute in Stockholm, Sweden. Other
researchers were Maj Hedehus and Michael E. Moseley of
the Stanford Department of Radiology and Elise Temple,
Talya Salz and Russell A. Poldrack of the neuroscience
program in the Psychology Department. Poldrack is now at
Massachusetts General Hospital and Salz is at the
Scientific Learning Corp. in Berkeley. SR
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