Fibers in the brain that bridge a region governing speech and another controlling the tongue may be less robust in stutterers than nonstutterers, new research finds. The study is among the few that have analyzed the brains of stutterers and is the first to focus on the white matter that connects brain structures.
Stuttering afflicts 1% of adults and has been around since the dawn of history: It's referred to in the Bible and on Egyptian hieroglyphs, says David Rosenfield of Baylor College of Medicine in Houston, Texas. A year ago, neurologist Anne Foundas at Tulane University Health Sciences Center in New Orleans, Louisiana, and her colleagues found subtle differences between stutterers and nonstutterers in two language regions, called Wernicke's area and Broca's area.
Neurologist Christian Büchel and his colleagues at the University of Hamburg, Germany, recruited 15 confirmed stutterers and 15 nonstutterers to dig deeper into the neuroanatomy of stuttering. The researchers performed a type of brain imaging called diffusion tensor imaging (DTI), which highlights the brain's white matter--the long nerve fibers made up of axons that send messages between neurons. Fibers running between two regions in the left side of the brain--one a speech center near Wernicke's and Broca's, the other a motor control region for the tongue and larynx--were about 30% less tightly packed among those who stuttered, the team reports in the 3 August issue of The Lancet. That suggests either that stutterers have fewer axons in this tract or that the axons meander, says Büchel.
In stutterers, "the whole system seems to be disrupted at multiple sites," says Foundas. She wonders whether the differences in brain anatomy that her lab found might induce these nearby changes in white matter.