Developmental stuttering affects about 5% of children. Most of these children recover during childhood resulting in only 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 increases if anxiety is high, the upcoming speech is particularly long, or grammatically complex. Fluency can be increased in some people who stutter by altering the feedback that people 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 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.
BRAIN STRUCTURE AND FUNCTION IN STUTTERING
We have used brain imaging to examine the brains of children and adults who stutter. Typically, there is no obvious brain abnormality associated with a developmental disorders such as stuttering. By using brain imaging, we hope to detect more subtle abnormalities relating to brain structure and function. 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 fluent-speaking controls. In the people who stutter, one area that was functionally abnormal - the ventral premotor cortex - was also found to have an underlying structural abnormality 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.
We also found that during speech production with normal feedback, activity in the motor and auditory areas of the brains of people who stutter is not well synchronized. When feedback is delayed, however, the activity of these areas becomes better synchronized. This finding provides clues to the mechanism that underlies the fluency enhancing effects of altered auditory feedback in people who stutter.
Currently, we are examining the motor performance and learning abilities of people who stutter, using behavioural tests and brain stimulation.
Connally EL, Ward, D, Howell, P, & Watkins, KE (in press) Disrupted white matter in language and motor tracts in developmental stuttering. Brain and Language.
Watkins KE, Klein D (2011) Brain structure and function in developmental stuttering and bilingualism. In: Stuttering and Language Diversity.ed. by Howell P & van Borsel J, chap. 4, Multilingual Matters, Bristol, England. Communication Disorders across Languages. (Müller & Ball, series Eds.)
Watkins KE (2011) Developmental disorders of speech and language From genes to brain structure and function. Prog Brain Res, 189:225-38.
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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