The findings are important, they wrote, because dyslexia accounts for 80% of all learning disabilities in the U.S. and U.K. and affects between 5% and 17% of the population.
"The majority of the dyslexic population are adults, many of whom suffer significant financial and emotional consequences," wrote the researchers. "Yet our knowledge about treatment outcomes for this population is relatively small, and the functional reorganization following treatment is unknown." The researchers pointed out that adaptive changes, or "plasticity," in the brains of adults, whose brains are mature, are likely to be different than in children with dyslexia, whose brains are rapidly changing with development.
To explore whether adult dyslexics can be helped, the researchers recruited for study 19 dyslexic adults and 19 adults who did not have dyslexia. They first compared brain function in the two groups using functional magnetic resonance imaging (fMRI). In this widely used technique, harmless magnetic fields and radio signals are used to scan blood flow in brain regions, which reflects brain activity.
The fMRI scans revealed that during a word processing task, the dyslexic subjects showed less activity in a region of the brain known to be involved in reading -- the left inferior parietal cortex.
In the task, both groups of subjects were asked to listen to words, then delete the initial phoneme -- for example, hear the word "cat" and repeat "at." As a control task, the subjects were asked only to repeat the words they heard, so the researchers could "subtract" any activity due to mental processing in general.
The researchers then gave half the dyslexic group intensive training in "phonological" tasks of recognizing and processing word sounds, while the other half received no such training.
When Eden and her colleagues retested both dyslexic groups, they found that the trained group showed significant improvement in visual and auditory word recognition and oral reading skills. Also, the researchers found that the trained dyslexic subjects showed increased activity in the left parietal cortex, as well as numerous regions in the right hemisphere of their brain.
"Together, these findings provide evidence that dyslexic adults are not, as may have been assumed, unable to profit from remedial practice," wrote the researchers. "In fact, the same strategies that are effective in teaching children phonological awareness skills are helpful in adults. Further, they are accompanied by neural changes known to underlie reading remediation of developmental dyslexia in childhood combined with those previously observed during the rehabilitation of adults with acquired dyslexia [due to brain damage].
"These findings provide important information for understanding adults with developmental dyslexia and for developing more specialized, effective interventions for this population," wrote the researchers.
Guinevere F. Eden, Karen Jones, Katherine Cappell, Lynn Gareau, Frank B. Wood, Thomas Zeffiro, Nicole Dietz, John Agnew, D. Lynn Flowers: "Neurophysiological Recovery and Compensation after Remediation in Adult Developmental Dyslexia"
Publishing in Neuron, Volume 44, Number 3, October 28, 2004, pages 411–422.
Journal
Neuron