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New Theory for Cause of Stuttering

Brain Abnormality Linked to Speech Disorder
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Aug. 1, 2002 -- A structural problem in the brain may be the cause of stuttering. According to a new study, this faulty wiring in the brain might explain why some children overcome their stuttering problem while others continue to suffer as adults.

Developmental stuttering is a speech disorder that causes involuntary repetition of words, lengthened sounds, or arrests of sounds. It affects about 4%-5% of all children between the ages of 3 and 5 years. Most children grow out of it, but stuttering persists beyond puberty in about 1% of adults.

Researchers say the condition is thought to be caused by a genetic defect, but until now the exact origin and mechanism of stuttering has been unclear -- despite decades of research.

In their study, researchers used MRI to determine the structure of brain tissue in 15 people with stuttering and 15 people with normal speech. In the stutterers, the area of the brain responsible for the planning and articulation of speech, found on the left side of the brain, was different than in the others.

Researchers say difficulties in the transmission of information between this area and the parts on the right side of the brain responsible for language prevent fluid speech.

Study author Cornelius Weiller, of the department of neurology at the University of Hamburg in Germany, and colleagues say the right side of the brain becomes overactivated to compensate for this problem in the left region.

This abnormality probably develops during the phase of development in which many children experience temporary stuttering, the authors write. "Our methods could be used to ascertain why certain children develop persistent stuttering whereas others become fluent speakers."

Previous studies have suggested that the process might work the other way around. According to this theory, the overactivation of the right side of the brain is the initial cause of stuttering, which leads to the eventual deterioration of the corresponding areas in the left side.

However, the authors of this study say this explanation is "extremely unlikely" since it is unclear how widespread overactivation in the right side could lead to abnormalities in the left.

The study appears in the Aug. 3 issue of The Lancet.

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