Tracing the brain's reading network.

A new study indicates that reading requires the angular gyms, a brain structure that maintains connections to areas involved in speech comprehension and the integration of alphabetic letters with their corresponding sounds.

The reading disorder known as dyslexia may often reflect an inability of the angular gyrus to work in concert with these related brain regions, hold neuroscientist Barry Horwitz of the National Institute on Aging in Bethesda, Md., and his coworkers.

Horwitz's team administered positron emission tomography, or PET, scans to 17 dyslexic men, all of whom had longstanding reading difficulties despite having IQs in the normal range, and 14 men who read well. Brain imaging was performed as participants read difficult nonsense words (such as "phalbap," in which "ph" would be pronounced as "f") and real words with unusual pronunciations (such as "choir").

For good readers, these tasks induced simultaneous blood flow surges on the left side of the angular gyrus and in several brain areas that integrate the visual and linguistic information needed for effective reading, the scientists report in the July 21 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES. The men with dyslexia exhibited increased activity in all of these areas except one--the left angular gyrus.

The new findings complement evidence that dyslexia may stem from disturbances in various parts of a brain network that begin working together during childhood as a result of continued exposure to written language, according to the researchers (SN: 3/7/98, p. 150).