Dyslexia Affects Hearing Process
Left Brain Activity Differs from Nonimpaired Readers
WebMD News Archive
Oct. 27, 2003 -- It is becoming increasingly evident that
people with dyslexia process sound and language differently from people who
don't have trouble reading.
Using a highly precise imaging technique, University of Texas
researchers compared brain activity in areas known to be associated with
analyzing the sound structure of written and spoken words in children with
dyslexia with children without reading problems. They found that the areas of
the left-brain associated with speech were highly active in the nonimpaired
readers and not very active at all in those who were dyslexic.
The findings are consistent with the idea that problems
understanding the "sound structure" of both written and spoken language
are associated with abnormal activity in this area of the brain, the
"We are not the only ones to find that this neurological
deficit appears to be confined to very restricted areas of the brain,"
researcher Joshua Breier, PhD, tells WebMD. "The evidence is overwhelming
that dyslexia is a very specific learning disability, and not a problem with
Left Brain, Right Brain
In this study, 12 children with dyslexia and 11 nonimpaired
children were given simple speech-perception tests. Brain activity was
simultaneously observed using a noninvasive imaging technique known as
magnetoencephalography (MEG). The findings are reported in the October issue of
the American Psychological Association journal Neuropsychology.
When the nonimpaired readers were distinguishing between
sounds, they showed more activity in the left part of the brain associated with
sound and speech. The children with dyslexia showed little activity in the
area, but after a time showed more activity in the corresponding, but
functionally mysterious, areas on the right side of the brain. The poorer the
performance on the speech-perception tests, the more the right side of the
brain "lit up" during testing.
In earlier studies the researchers found similar patterns of
brain activity in dyslexic and nonimpaired children tested while they were
Breier tells WebMD that it is not yet clear whether the
right-sided brain activity seen in children with dyslexia occurs as an attempt
to compensate for the left-brain inactivity, but other recent studies do show
that this is the case.