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Stanford Report, March 1, 2000

Brain abnormality linked to dyslexia

BY KATHLEEN O'TOOLE

Researchers at Stanford have for the first time found clear evidence that some reading problems are tied to a specific defect in neuron function, according to a report published in the February issue of the journal Neuron.

"We found that adults with reading deficits have an abnormality in white matter of the brain, which is vital for transmitting information between the brain areas involved in language comprehension," said psychology Professor John Gabrieli, who was the senior researcher on the study team.

The white matter abnormality may indicate that the neuron's myelin is defective, he said. A neuron sends vital messages in the brain by transmitting electrical signals along an extended appendage called an axon. The axon often is covered with an insulating fatty sheath, known as myelin, that speeds up the transmission of the signals. Myelin is a major constituent of white matter.

In the study, the researchers examined the brains of six adults with a history of dyslexia and 11 adults who had no history of reading difficulties using a new technique involving magnetic resonance imaging. The scanner gauged the cellular structure of the white matter by measuring the microscopic movement of water molecules in the brain. Abnormal water movement indicated faulty white matter, Gabrieli said.

The researchers found that the dyslexic group had poor functioning white matter that may therefore slow message transmission in the regions that are thought to connect the language processing areas of the temporal and frontal lobes of the brain.

"We also found that the level of reading performance of the dyslexic group, as well as the healthy group, related to white matter function," Gabrieli said. In the dyslexic group the poorest readers had the poorest functioning white matter, and in the healthy group the poorest readers had the poorest functioning white matter.

The researchers hope that in the future physicians will be able to use the noninvasive imaging technique to identify children at risk for reading impairments so that they can benefit from early intervention.

The lead author of the Neuron article is Torkel Klingberg, a former Stanford postdoctoral researcher in Gabrieli's neuroscience lab who is now in the Department of Neuroscience at Karolinska Institute in Stockholm, Sweden. Other researchers were Maj Hedehus and Michael E. Moseley of the Stanford Department of Radiology and Elise Temple, Talya Salz and Russell A. Poldrack of the neuroscience program in the Psychology Department. Poldrack is now at Massachusetts General Hospital and Salz is at the Scientific Learning Corp. in Berkeley. SR