Map of the human brain sheds new light on dyslexia

Apr 20 2006

Mapping the human brain at The University of Auckland has revealed that abnormal brain activity appears to be the reason why some dyslexia sufferers find it difficult to learn to read.

The research team at the Department of Psychology in the Faculty of Science, headed by Dr Karen Waldie, is using functional magnetic resonance imaging (fMRI) to map the patterns of activity in the brains of normal readers and adults with dyslexia. The new study used the University's recently installed fMRI machine, the first of its type in New Zealand, to non-invasively monitor blood flow in the brain during specific reading tasks.

Dyslexia affects about seven percent of the New Zealand population and there is no known cure, although it is thought that greater understanding of the underlying neurological basis of the condition will assist in better diagnosis and management. Phonological dyslexia is the most prevalent, affecting about 70 per cent of children with reading difficulties caused by dyslexia. Children with phonological dyslexia are unable to decode written words phonetically - that is, associate sounds with letters - resulting in great difficulty reading unfamiliar and non-words.

The University of Auckland study showed mostly left hemisphere brain activity when normal readers were asked to perform three different reading tasks, including a phonics-based reading task where letter strings must be silently sounded-out to get the correct answer. In contrast, the dyslexic adults showed very limited left-brain activity during these tasks, with most activity being in the right brain.

"For over 80 years, scientists have been searching for the reason why otherwise intelligent and motivated children have difficulty learning to read," commented Dr Waldie. "With the use of these new imaging techniques, we have been able to show a striking difference in brain activity between normal reading adults and adults with phonological dyslexia."

"The only significant activity in the phonological dyslexic group was in the frontal lobes of the right hemisphere of the brain," she continued. "This might be the result of the dyslexic brain trying to compensate for an inefficient left-brain language system - a system that might have been compromised during brain development or is simply genetically hard-wired to be a bit different from the norm."

Additional research will focus on whether the brain patterns observed reflect a fundamental brain anomaly or are a long-term response to reading difficulties. Currently, Dr Waldie's team is looking for a further five adults aged 18-38 years, with a history of severe reading problems, to take part in the study, which involves performing various reading tasks while the brain is scanned using the fMRI machine.