Stuttering starts in the brain

U. ILLINOIS (US) — New research is suggesting that atypical brain function is a fundamental aspect of speech production tasks for adults who stutter.

Previous researchers have suspected that anatomical differences in areas of the brain involved in speech production play a critical role in stuttering.

Anatomical differences in the hemispheres of the brain between adults who stutter (AWS) and normally fluent adults (NFA) have long been thought to play a role in their different speech outcomes.

The new research shows atypical brain function and right predominant lateralization in AWS even while they are performing simple speech production tasks.

Torrey Loucks, a researcher with the Stuttering Research Project at the University of Illinois, and colleagues focused on differences between AWS and NFA in the corpus callosum of the brain. The study included 11 male AWS and 12 male NFA between 20- and 35-years-old.

The corpus callosum—responsible for most interhemispheric transfer of information between the left and right cerebral hemispheres—the rostrum and anterior midbody sections—were larger in AWS than NFA, and that this structural difference, “may be associated with the atypical functional brain organization in AWS and may be a factor in the performance of AWS on (language-relevant) tasks.”

Past research has also shown that adults who stutter exhibit atypical brain symmetry and distributions of gray and white matter tissue across the cerebral hemispheres.

Published in the Journal of Communications Disorders, the study that focuses on the corpus callosum suggests that AWS “may have not established the dominance of one hemisphere for certain language tasks.

“Now because many speech areas are interconnected across the two hemispheres through the corpus callosum, it might suggest that hemispheric dominance for speech and language has not been established to the same degree as it has been for normally fluent adults.”

Loucks then used functional magnetic resonance imaging of brain activity to study participants who stutter and found that even brief, simple speech tasks—such as producing a single word to name a picture—is associated with altered functional activity in the cortex and sub-cortical structures of AWS.

It was also clear that functional brain activity across several language relevant areas in AWS was predominantly lateralized to the right hemisphere of the brain.

“Altered hemispheric organization seems to be part of the basic organization of speech production in persons who stutter, and this differs fundamentally from the left lateralized activation that we see in normally fluent people,” Loucks says.

“This has been suspected and shown in studies by other investigators but typically with longer paradigms and more complicated speech tasks. The fact that you can even see this with single word picture naming suggests that it’s a fundamental aspect of their speech production network in the brain.

“There’s a lot of research going on with imaging and stuttering, but our work is making an important contribution because it shows that these differences are likely associated with automatic mechanisms that have some structural basis,” Loucks  says.

“It’s not just where the brain is activating, but that these changes in activation are associated with changes in the wiring of the brain as well.”

The next challenge is to translate these findings into interventions for stuttering. A series of ongoing studies by Loucks and his collaborators have shown that modifying how AWS hear their voice changes their coordination pattern of speech articulation that is associated with a reduction of stuttering occurrences.

“We’ve found that persons who stutter are remarkably dependent on hearing their own voice,” Loucks says.

“By changing their auditory feedback, or more specifically by introducing a slight delay in the time which persons who stutter hear their own voice, we saw an improvement in their speech coordination.

“Delayed feedback is known to have opposing effects on fluency but these effects on speech movement coordination that correlates with improved fluency is a new discovery. We think that enhancing speech coordination may open a window into more automatic ways to modulate speech fluency.”

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chat6 Comments


  1. Martin Schwartz

    Stutterers are invariably fluent when they talk to themselves out loud alone. They virtually all attest to this when queried. How does this square with the brain difference studies that are now so popular?

  2. Pam


    I’m stutterer and I am not fluent when I talk to myself out loud alone. Your generalization is wrong.

  3. Shrewsbury

    I often have difficulty speaking to myself. One does tend to be more fluent when speaking to oneself, but this is unsurprising when you consider that there is much less general information being processed than when one is speaking to others and interacting with them, and, what is more, the content tends to be far more basic, e.g. no narratives. (I liken it to how, in the early days of personal computing, a printer would stop (or stop and start and stop and start) if you tried to work on another program at the same time you were trying to print something out. I believer “stutterers” are simply processing more information than the speech-output centers of the brain can handle. This can be either because they are processing unusually large amounts of information, or because they have deficient speech areas.

  4. Diane

    I have struggled with stuttering at times and, for me, there seemed to be a strong correlation with how much of an anti-depressant I was taking (Wellbutrin). When the dosage was lowered, the stuttering subsided for the most part.

  5. Bijan Shafiei

    I am a speech and language pathologist and working in Iran. I think we can not generalized a rule for all stutterers. Every stutterers has an individual condition and may he/she treats individually and different from another stutter. But most of stutterers have a fluent speech when they are alone or signing or talk to themselves or a pet.
    It seems the brain of every stutterer works in a different way and it is related to the way that he/she learn to speak and overcome on his/her stuttering. During the long time, the braing learns a different way to processing and controling of their speech. So, there are a lot of treatment method and techniques for overcoming on stuttering which are useful for every stutterers.
    I am agree with Martin but not as a generalized rule. There are a lot of differences between stutterers.

  6. jacky

    I have started stuttering and stammering since I was 10. With time it got worse. Apart from this I used to see spots on my vision at times. Then at the age of 36 a huge brain tumor was discovered. It ruined part of my vision. After it was partially removed I still stutter sometimes, especially when I am in front of a crowd. So my idea is best to make an mri asap before the problem grows and does damge.

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