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Researcher explores the causes of stuttering

August 4, 2001

Heather Heilman

Stuttering is a debilitating problem that affects about five percent of children and one percent of the adult population. There are treatments, but none are completely effective. Stuttering is not caused by nervousness or lack of intelligence. But its actual causes are still something of a mystery.

Anne Foundas, associate professor of neurology, has discovered evidence of anatomical differences in the brains of adults with persistent developmental stuttering. Foundas and her research group studied 16 adults who stuttered and 16 fluent adults matched for age, gender, left or right handedness and education level.

MRI images revealed that the planum temporale, a part of the brain involved in higher-order auditory processing, was often larger in persistent stutterers. At the same time, there was less difference in size between the planum temporale on the left and right sides of the brain. In most fluent, right-handed adults, it's larger on the left side. Many of the stutterers also had more gyri, or bumps, in a particular part of the brain.

"This is the first evidence to suggest that brains of people who stutter are different and that atypical anatomy within these speech and language areas may be a risk factor," Foundas said. "We didn't find one feature that was uniformly distinct in these individuals. For example, in right-handed men who stutter, a large number of them had extra gyri as well as atypical anatomy of the planum temporale. In contrast, the right-handed women had more typical planum temporale, but they all had extra gyri. So we need to pursue this in a larger sample."

Interestingly, Foundas was not able to find any left-handed women who stutter. Stuttering is a problem that is more prevalent in males. In children, boys who stutter outnumber girls by about 5-to-1. In adults, there are twice as many male stutterers as female. Gender differences in brain anatomy are the likely explanation.

In women, for example, there is often less of a size difference between the left and right sides of the brain than there is in men. Researchers still don't know if different brain anatomy causes stuttering, and if so how. A better understanding of the neural mechanics involved would allow for the development of better treatment.

"Right now, treatments are limited and their effects may be transient," Foundas said. "But stuttering can be a real handicap."

She has received a grant from the Dana Foundation for a treatment study using functional MRI imaging. She will compare stutterers who receive behavioral treatment to those who are treated with a dopamine-blocking drug. Functional MRI will allow researchers to look at how the different treatments affect brain activation, in order to see if the brain actually works differently when fluency is induced.

Foundas said this should provide a better understanding of the differences in brain anatomy and function between those who stutter and those who don't, which would be useful information in the development of better treatments. It could also lead to early detection of children who are at risk of stuttering, perhaps allowing for intervention before the problem becomes manifest. In the meantime, the results of the original study will be published in July in the journal Neurology.

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