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Developmental stuttering affects about 5% of children. Most of these children stop stuttering during childhood resulting in 1% of adults with persistent developmental stuttering.  Speech dysfluencies that characterize stuttering are hesitations, prolongations and repetitions of speech sounds, typically occurring at the beginnings of words and sentences.  The amount of stuttering can increase if anxiety is high, the upcoming speech is particularly long, or grammatically complex.  Fluency can be temporarily enhanced in some people who stutter by altering the feedback that they hear of their own speech.  Small, barely noticeable delays or changes in the pitch of this feedback can be effective.  Other ways of enhancing fluency include speaking in unison with other people ("chorus" speech), with a rhythmic cue (metronome-timed speech) or speaking in a non-natural way, such as adopting a foreign accent.  Part of our research aims to understand how these fluency-enhancing techniques work and to find ways of prolonging their effects. 


We have used brain imaging to examine the brains of children and adults who stutter.  Typically, there is no obvious difference visible to the naked eye that could explain why someone stutters.  By using brain imaging, we can detect more subtle differences in brain structure and function in people who stutter.  We used diffusion tensor imaging (DTI) to examine white matter integrity and functional MRI to see the brain areas involved in speech production.  During sentence reading, we found a number of brain areas that were underactive and overactive in people who stutter compared to controls who do not stutter.  In the people who stutter, one area that was functionally underachieve - the ventral premotor cortex - was also found to have an underlying structural difference in the white matter pathways in the same region.  This pathway and the cortical areas it connects appear important therefore for the production of fluent speech. 

Recently, using MRI scans we found increased concentration of iron in the brains of people who stutter in the parts of the brain involved in movement initiation and control.  These new findings might relate to some of the genetic findings that are thought to cause stuttering in about 10% of people who stutter.  We don't yet know if stuttering causes the increased iron in the brain or whether stuttering is caused by increased iron.  More studies following people who stutter longitudinally from early in development are needed.  

Brain stimulation to enhance fluency

In a randomised controlled trial, we used transcranial direct current stimulation coupled with choral reading and metronome-timed speech to enhance fluency in people who stutter.  A very weak electrical current was applied over the scalp for 20 minutes a day while people used these fluency enhancers for five consecutive days.  This reduced speech disfluency measured a week later and was still reduced six weeks later.  A group who had the fluency enhancers but coupled with "sham" stimulation (the stimulator was turned on briefly and off again so people could not tell if they had real or sham stimulation) showed no change in their fluency.  We are currently analysing the data from a follow-up study. Listen to Jen Chesters talk about these results.

MRI Scans of the vocal tract during speaking

Recently we used vocal tract MRI to visualise movements during fluent and disfluent speech in people who stutter.  We found that speech movements are more variable in people who stutter even when speech is perceptibly fluent.  


Cler GJ, Krishnan S, Papp D, Wiltshire CEE, Chesters J, Watkins KE. Elevated iron concentration in putamen and cortical speech motor network in developmental stuttering. Brain. 2021 Nov 29;144(10):2979-2984. doi: 10.1093/brain/awab283.

Wiltshire CEE, Chiew M, Chesters J, Healy MP, Watkins KE. Speech Movement Variability in People Who Stutter: A Vocal Tract Magnetic Resonance Imaging Study. J Speech Lang Hear Res. 2021 Jul 16;64(7):2438-2452. doi: 10.1044/2021_JSLHR-20-00507.

Chesters J, Möttönen R, Watkins KE. Transcranial direct current stimulation over left inferior frontal cortex improves speech fluency in adults who stutter. Brain. 2018 Apr 1;141(4):1161-1171. doi: 10.1093/brain/awy011.

Watkins KE, Smith SM, Davis S & Howell P (2008) Structural and functional abnormalities of the motor system in developmental stuttering. Brain, 131(Pt 1):50-59.

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