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From: Larry Molt
Date: 31 Oct 2005
Time: 21:59:23 -0600
Remote Name: 68.190.61.215
That's a very interesting question, Robert. The (lack of normal) hemispheric dominance theory has gone through a variety of permutations and has fallen in and out of favor since Orton and Travis presented it in the late 1920's. Travis himself abandoned the theory and moved to a psychoanalytical framework in the the 1950's, then later recanted that model and moved back to supporting a neurological model in his last publications. It saw resurgence several times as new assessment tools appeared. (For example, Robert Jones' work with the WADA test in the early 1960's, Curry and Gregory in the late 60's and Toscher and Rupp in the late 70's with central auditory processing tests, Skip Moore with EEG alpha suppression asymmetries in the 1980's,and again in the 1990's as SPECT and PET studies investigating regional cerebral blood flow asymmetries appeared, and more recently with fMRI. Since 2000 there have been MRI studies demonstrating left and right hemisphere morphological asymmetry, and most recently, hemispheric differences appearing with magnetoencephalography imaging). Unfortunately, even with the most recent brain imaging research, it is unclear where asymmetries may actually exist, with left/right differences noted across studies in a wide variety of CNS sites, including both anterior and infero-postero frontal lobe regions, the supplementary motor area, and various temporal and parietal lobe sites cortically; anterior (and possibly posterior) cingulate gyrus and other corpus striatum/basilar gangliar regions subcortically; and in the cerebellum. Asymmetries have been noted in a very diverse variety of both speech and non-speech conditions, and what is seen appears to vary with the task that is required. Additionally, to futher confuse the issues, the left/right differences are typically not evidenced in all stuttering participants in any particular study, and may vary across severity groupings. In short, while we have lots of tantilizing evidence of differences in neurologic activity in people who stutter, we have no clear knowledge of what to work on, or even the role of the differences that have been observed in producing disfluent or fluent speech. Consequently, it seems to be far too early to think about assistive devices that may mediate changes in hemispheric activity. They certainly are not out of the question, and may eventually be an important adjunct to therapy for stuttering, but my crystal ball is looking just too foggy to speculate any further!