Unsolved Mysteries: Stuttering Edition

March 7, 2024

Written by: Stephany Daniel, Soo-Eun Chang

What We Know About Stuttering

Genetics play a role

While more research is needed to fully understand the genetic component of stuttering, there are several major clues that stuttering can be passed down in families. The first signs of this were discovered by studying twins. These studies found that if one twin stuttered, it was far more likely that the other twin would also stutter if the two were identical. Because identical twins share the exact same DNA, this was an early sign that genes could contribute to stuttering. More studies have found that about half of all people who stutter report having at least one family member who also stutters. Further genetic testing has identified a few gene variations that are common in families where many members of the family stutter. We also know that females are more likely to recover from stuttering than males, showing sex-related differences in recovery. In time, researchers may be able to identify how these genetic factors are connected to the brain changes associated with stuttering. Speaking of which, our lab’s previous publications were some of the first to attempt connecting the dots between gene mutations associated with stuttering and brain structure and functional differences observed in children who stutter.

Stuttering is associated with changes in the brain

While finding stuttering in the brain isn’t as easy as finding a broken bone with an x-ray, over two decades of research studies have found strong evidence that the brains of people who stutter are subtly different from the brains of those who recover from stuttering or have never stuttered at all. Human speech is a complex process that relies on many parts of the brain working together harmoniously and at rapid timescales. In the brains of people who stutter, some of these parts of the brain are less active or their connections to one another appear to be interrupted. Researchers, like those in our lab, continue to look closely at brain images from their studies to better understand these differences.

Some people recover from stuttering as they get older

At least 80% of children who stutter will “grow out” of stuttering by the time they reach adolescence or adulthood. The same studies that show differences in the brains of children who stutter also show that these differences begin to fade as children recover from their stuttering. The parts of their brain that were less active become more active as they recover and the connections between them form stronger links. Looking more closely at these recovery patterns, as we do through our lab’s longitudinal study, will help researchers sort out why some brains undergo this recovery process and some don’t.

Stuttering treatments are limited, but speech therapy can help some adults

While there is no complete cure for stuttering, research into the effectiveness of stuttering therapy shows that it can make a difference for some adults and improve their quality of life. Research has found that the brain is responsive to stuttering therapy, increasing activity in parts of the brain crucial to fluent speech. These studies point to the concept of neuroplasticity—the idea that our brains are not in a “fixed” state and are capable of growing and changing with the right training. 

The Biggest Mysteries of Stuttering

People don't stutter when they sing

Even people with severely-pronounced stuttering can achieve fluent speech when singing. To understand why this is the case, researchers are looking into which parts of the brain control speech and which parts control singing to identify any key differences in those areas. As with speaking, singing requires many parts of our body—from our brain to our voice box— to work closely together. Breaking down why singing connections are stronger than speaking connections can offer a big clue into this mystery!

Stuttering is social

Another common phenomenon among people who stutter is that many report that their stuttering is absent when they speak only to themselves. It’s not until they speak in a social context, that is, to other people, that their stuttering returns. This may be where the common myth that stuttering is caused by nervousness came from. In reality, the situation is far more complex. For example, researchers have identified changes in parts of the brain that are associated with “reward-centers” in people who stutter. These reward centers are why eating a piece of delicious chocolate feels so satisfying. The brain also considers speech an enjoyable activity that builds stronger social bonds. In the brains of people who stutter, that connection isn't as strong. The biggest question? Do these changes in the reward centers of the brain point to a cause of stuttering? Or are changes in that area of the brain the result of experiencing a lifetime of stuttering and the challenges that come with it?

Boys are more likely to stutter than girls

In childhood, the male-to-female ratio of stuttering is about 1:2. In adults, only one out of five chronic stutterers is a woman. Stuttering in adulthood is significantly more common in men, leading researchers to wonder about sex-related differences. Researchers believe it is possible that the higher incidence in men is related to a combination of genetic and hormonal factors. It is possible that estrogen plays an important role in stuttering recovery, but more research is needed to understand how.