|Latest Research Lends Support to
"Reactive Inhibition" Theory of Stuttering
Research results published in the August 2000 issue of the Journal of Speech, Language, and Hearing Research indicate that the subcortical, limbic areas of the brains of people who stutter are more active during oral production of low-imagery words than during a silent reading task of the same words. They are also much more active than the same areas in the brains of fluent speakers during oral reading.
These results lend support to theories that emphasize the importance of reaction and inhibition in the development and maintenance of this chronic speech disorder. Here-to-fore, researchers have thought that the major differences between fluent and dysfluent speakers would be found in the right and left hemispheres of the cerebral cortex. While the right hemispheres of the brains of people who stuttered were also more active while they were reading aloud, this activity was not seen in the right hemisphere region that mirrors the left hemisphere motor planning and speech-motor areas. Such increased activity would be required to attribute stuttering to anomalous or disordered lateral dominance for speech-motor activity.
While the scientists responsible for the research, Luc de Nil and Robert Kroll, identified the areas of increased activity only as being "in the region of the thalamus," the brain imaging results provided in their paper indicate that the areas include those involved in inhibitory responses in the anterior cingulate cortex, a region associated with speech and emotions, and the limbic system, which mediates fear and threat responses. While the cingulate cortex regions of fluent speakers also showed higher activity during the speaking task, activity of the central subcortical area occupied by the thalamus and the so-called "Papez Circuit" implicated in emotional responses such as fear and anger was not shown to be increased when fluent speakers engaged in oral reading of the same low-imagery words.
De Nil and Kroll attributed the higher limbic activity to "anticipatory" and "rehearsal" behavior, in support of the motor speech task orientation of present stuttering research. This point of view focuses on mechanistic explanations of stuttering. By contrast, the reactive inhibition theory of stuttering attempts to account for the fear and threat responses that are known to be prevalent in stuttering behavior and which are said by most neurological researchers working in other areas to be key elements of the brain's automatic attention system.
De Nil, LF, Kroll, RM, Kapur S, Houle, S, (2000), A positron emission tomography study of silent and oral single word reading in stuttering and nonstuttering adults. Journal of Speech, Language, and Hearing Research, 43: 1038-1053.
© 1994 - 2003 Darrell M. Dodge
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Last Updated: Saturday, March 21, 2009