Monday, August 9, 2010

Parkinson's Disease, Dopamine, and Stuttering

In the previous blog entry, we discussed the possibility of a nocebo-like effect having an influence on stuttering. Basically, the context in which an individual finds himself can have a negative effect on his fluency. This is a result of a conditioning mechanism whereby a specific context is associated with greater disfluency.

Victims of Parkinson's disease have a deficit of dopamine activity in the same area of the brain in which stutterers have an overabundance. And an interesting observation is that Parkinsonism patients receiving a placebo showed a substantial increase of dopamine activity in this part of the brain according to brain imaging results. So we can wonder if, similarly, the nocebo-like effect of context on stuttering might also increase the level of dopamine activity in the brains of stutterers, thus negatively affecting their fluency.
The diagram discussed in the blog entry entitled "Mind/Body Problem" is repeated here with the specific labels related to stuttering replacing the generalized labels of the previous diagram.  Note that the "Anxiety" label was replaced with the "Mind" label since anxiety can be viewed as a state of the mind.  So basically, stuttering affects the mind (i.e., causes anxiety) which in turn affects stuttering.  In addition, the context (e.g., speaking before an audience), through conditioning, further affects the mind and the subsequent lack of fluency.
However, given the possible dopamine connection discussed above, we can modify the diagram as follows:

 Note that the directed line now goes from "Mind" to "Excessive Dopamine Activity) instead of going to the "Stuttering" node, reflecting the possibility that context, acting as a nocebo, will directly affect dopamine activity which in turn affects fluency. This representation of the mechanism for stuttering has the advantage of following the law of parsimony in explaining stuttering.

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