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Brains, reading & stuttering

Pete Wilton

 January sees the release of The King's Speech, a movie in which Colin Firth stars as George VI, portraying the King's struggle to overcome his stutter.

But how much do we understand about the processes that cause stuttering?

Yesterday, Kate Watkins of Oxford University's Department of Experimental Psychology presented new research at the Neuroscience 2010 conference into the brain activity of people who stutter and how it differs from the brain activity of other people during reading and listening.

I asked Kate about her latest work and how close we are to understanding what causes this condition...

OxSciBlog: What had previous research found out about the brain activity of people who stutter?
Kate Watkins: Previous studies have scanned the brains of people who stutter while they speak out loud in the scanner. Several abnormal patterns of activation are seen under these conditions: people who stutter activate right hemisphere regions that are homologous with regions active during speech production in the left hemisphere; brain regions responding to the speech sounds produced (auditory cortex) tend to be underactive in people who stutter compared to fluent speakers; subcortical brain regions involved in movement planning, sequencing, timing and execution (eg the basal ganglia and cerebellum) are typically overactive during speech production in people who stutter.

The majority of studies done previously have used overt speech production. This may or may not have included stuttered speech in the people who stutter (one curious effect of scanning that we observed was a reduction in stuttering when speaking inside the scanner). Using overt speech production raises some problems for data acquisition but, more importantly, it is not possible to tell if the abnormal patterns of speech production are a cause or a consequence of stuttered speech. 

OSB: How did you study brain activity in this new research?
KW: We used functional MRI to scan the brains of people who stutter and fluent speaking control participants during three conditions: (i) while they listened to sentences; (ii) while reading sentences silently; (iii) while reading sentences and listening to the same sentence being read by someone else. We wanted to know if the same patterns of abnormal brain activity would be seen in people who stutter even when they are not producing speech.  

OSB: What differences did you find in brain activity between people who stutter and non-stutterers?
KW: We found abnormal patterns of activation in people who stutter in auditory and motor brain areas but these patterns were different to those seen previously and during speech production. In contrast with previous findings, the auditory areas of the brain that responded to listening to other people speaking showed more activity in the people who stutter than the controls; when listening to self-produced speech this region typically had less activity in stutterers than in controls.

Together these findings suggest the reactivity of the auditory system is abnormal in stutterers. When reading, people who stutter showed abnormally reduced activity in a motor circuit that included the left inferior frontal gyrus, putamen and supplementary motor area. The activity in this motor circuit was reduced even further when listening to speech. This circuit is involved in initiating and sequencing of movement.

Even though the people in our study didn't produce any movements related to speech, this circuit is still involved in internal speech and its activity is abnormal in people who stutter. Our findings can therefore be considered to be characteristic of the stuttering brain rather than simply reflecting differences related to stuttered speech production. 

OSB: What is the next stage in your research?
KW: Next we want to look at the circuitry between the abnormal brain regions in more detail. The integration of auditory information in the motor system seems to be important for highlighting the functional abnormalities that we saw. We want to look further also at how the known fluency enhancers work in people who stutter - that is we need to figure out their mechanism of action in the brain and possibly implement methods for improving the therapeutic efficacy of this enhancement. 

OSB: What other research needs to be done if we are to understand what causes stuttering?
KW: Longitudinal studies starting early in childhood when stuttering starts are required. Ideally, we would like to study children soon after they start to stutter and follow up those who spontaneously recover and those that persist in stuttering. Genetic studies also have potential to shed light on the causes of this disorder. Mutations in three genes have been identified already that occur in about 10% of people who stutter but how they cause stuttering is unclear.