Others, meanwhile, are delving into the root causes of stuttering, which also may point to novel treatments. In past decades, therapists mistakenly attributed stuttering to defects of the tongue and voice box, or to anxiety, trauma, or even poor parenting—and some still do. Yet others have long suspected that neurological problems might underlie stuttering, says J. Scott Yaruss, a speech-language pathologist at Michigan State University. The first data to back up that hunch came in 1991, Yaruss says, when researchers reported altered blood flow in the brains of people who stuttered. Over the past three decades, continuing research has made it more apparent that stuttering is all in the brain.
“We are in the middle of an absolute explosion of knowledge being developed about stuttering,” Yaruss says.
There’s still a lot to figure out, though. Neuroscientists have observed subtle differences in the brains of people who stutter, but they can’t be certain if those differences are the cause or a result of the stutter. Geneticists are identifying variations in certain genes that predispose a person to stutter, but the genes themselves are puzzling; only recently have their links to brain anatomy become apparent.
Maguire, meanwhile, is pursuing treatments based on dopamine, a chemical messenger in the brain that helps regulate emotions and movement. (Precise muscle movements, of course, are needed for intelligible speech.) Scientists are just beginning to braid these disparate threads together, even as they forge ahead with early testing for treatments based on their discoveries.
Looking at a standard brain scan of someone who stutters, a radiologist won’t notice anything amiss. It’s only when experts look with specialized technology that shows the brain’s in-depth structure and activity during speech that subtle differences between groups who do and don’t stutter become apparent.
The problem isn’t confined to one part of the brain. Rather, it’s all about connections between different parts, says speech-language pathologist and neuroscientist Soo-Eun Chang of the University of Michigan. For example, in the brain’s left hemisphere, people who stutter often appear to have slightly weaker connections between the areas responsible for hearing and for the movements that generate speech. Chang has also observed structural differences in the corpus callosum, the big bundle of nerve fibers that links the brain’s left and right hemispheres.
These findings hint that stuttering might result from slight delays in communication between parts of the brain. Speech, Chang suggests, would be particularly susceptible to such delays because it must be coordinated at lightning speed.
Chang has been trying to understand why about 80 percent of kids who stutter grow up to have normal speech patterns, while the other 20 percent continue to stutter into adulthood. Stuttering typically begins when children first start stringing words together into simple sentences, around age 2. Chang studies children for up to four years, starting as early as possible, looking for changing patterns in brain scans.