This is a follow up to my previous post on the (reduced) effect of delayed auditory feedback (DAF) in conduction aphasia. Here we consider the possible relation between anatomical abnormalities in the planum temporale and DAF in stutterers.
Paradoxically, DAF can improve fluency in people who stutter (it decreases fluency in control subjects). Some stutterers also have an anatomically atypical planum temporale. A study published in Neurology by Foundas et al. (2004) sought to determine whether there was a relation between the paradoxical DAF effect and planum temporale anatomy. There was: stutterers with atypical planum temporale asymmetries (R>L) showed the paradoxical DAF effect, whereas stutterers with typical planum asymmetries did not show the paradoxical DAF effect.
This line of investigation provides a further bit of evidence linking an auditory-motor integration system to the planum temporale. Our functionally defined area Spt (e.g., Hickok et al., 2003), which we believe supports auditory-motor integration, is located in the posterior portion of the left planum temporale. I suspect that it is this region that is somehow implicated in stuttering. Why the symptoms of conduction aphasia and developmental stuttering are different is an important question (assuming that some aspect of the same system is involved)...
Other disorders have been linked to planum temporale (dys)function including dyslexia, schizophrenia, and autism. I seriously doubt that dysfunction of the auditory-motor integration system involving the planum is going to explain the speech/auditory symptoms of all these disorders as there are probably lots of ways to disrupt speech/auditory functions. Following the example in the Foundas et al. study, I wonder if planum temporale atypicalities plus DAF effects might be used in combination to better characterize what might be going on in these disorders.
A. L. Foundas, MD, A. M. Bollich, PhD, J. Feldman, MD, D. M. Corey, PhD, M. Hurley, PhD, L. C. Lemen, PhD and K. M. Heilman, MD (2004). Aberrant auditory processing and atypical planum temporale in developmental stuttering Neurology, 63, 1640-1646
Gregory Hickok, Bradley Buchsbaum, Colin Humphries, Tugan Muftuler (2003). Auditory–Motor Interaction Revealed by fMRI: Speech, Music, and Working Memory in Area Spt Journal of Cognitive Neuroscience, 15 (5), 673-682 DOI: 10.1162/089892903322307393
M LINCOLN, A PACKMAN, M ONSLOW (2006). Altered auditory feedback and the treatment of stuttering: A review Journal of Fluency Disorders, 31 (2), 71-89 DOI: 10.1016/j.jfludis.2006.04.001
This is a timely post as I am in the midst of preparing a submission on the topic. Auditory integration in people who stutter is the focus of my doctoral thesis research. The submission will present MEG results comparing auditory M100 amplitudes during passive listening to vowel and word stimuli to overtly speaking those same stimuli aloud in adults who stutter and adults who are fluent speakers. The study builds on the work of John Houde and others who have attempted to understand the suppression of M100 response during speaking as well as the work of Max et al. who have proposed theories of the role of auditory feedback in developmental stuttering. Anyone who is interested in discussing my results further pre-publication is welcome to email me at:
d (dot) beal (at) utoronto.ca
I am in the process of collecting a similar dataset in school-age boys who stutter. As the onset of stuttering is in the preschool years I am cautiously optimistic that the results of the study will allow us to provide novel insight into the disorder.
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