Sounds like dyslexia.

Scientists have tentatively linked the reading disability known as dyslexia to a bevy of brain disturbances. A team of neuroscientists now adds to this collection a disruption of the brain region that mediates perception of brief, rapidly presented sounds.

Lifelong reading problems may often stem, at least in part, from glitches in an area of the brain's sound system thought to be crucial for identifying speech sounds, contend Srikantan Nagarajan of the University of California, San Francisco (UCSF) and his coworkers.

"We believe that adult dyslexics are not delivering normal forms of representation of the separate sounds in words to brain regions involved in speech perception and reading," says study coauthor Michael M. Merzenich, also of UCSF.

The new study, published in the May 25 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES, compared seven people who have severe reading difficulties typical of dyslexia with seven competent readers. All were between 18 and 42 years old and had average scores on intelligence tests.

Only the poor readers scored low on a test of the ability to discriminate between pairs of briefly heard sounds. Each acoustic duo consisted of any of four combinations of high-and low-frequency tones (high-high, high-low, low-high, low-low). After presentation of a sound pair, volunteers signaled which combination they had heard by pressing buttons strapped to their thighs. A computer stored their responses.

During these trials, sensors placed over the scalp measured magnetic fluctuations generated by the electrical activity of large numbers of neurons. The UCSF team focused on activity in the brain's primary auditory cortex, which sorts out sounds that can serve as components of words.

Competent readers readily identified the sound sequences. Poor readers did report hearing each pair of sounds, and they could often tell when the two sounds differed. They usually erred, however, in selecting the correct sequence.

Moreover, individual tones evoked weak and disorganized responses in the primary auditory tissue of poor readers, in contrast to strong, clear responses in competent readers. Other recent studies have implicated brain disturbances affecting language comprehension and visual perception in dyslexia (SN: 3/7/98, p. 150).