Tuesday, May 10, 2005

What's cause and effect?

Last time I described that Brown, Ingham, Ingham, Laird and Fox proposed a theory based on the efference copy concept to explain the differences in brain activation for PDS. Here are a few quick&dirty comments:

1) The explanation of overactivation in the cerebellar vermis and the lack of activation in auditory regions using the concept of efference copy seems reasonable and makes sense to me. I am not really an expert, so I cannot say more about it.

2) They provide testable predictions, which is always good.

3) The theory only focusses on explaining the observed difference in brain activation. So it's not really a theory of PDS, and leaves many questions open like genetics, gender difference, why fluency-inducing work, and much more. So it's just the beginning...

3) They assume that the problem really starts in unsucessful initiation of speech motor plans. So paradoxically that could lead me to conclude that all the observed functional activation differences in the PDS brain in fMRI and PET is not really about PDS (as I have been preaching to everyone for years), but only effect or symptons of the disorder like disfluent speech.

4) In this respect, I found their explanation of motor region overactivation quite vague, and I am not sure that they are all consequences of unsucessful initiation or low skilled regions that need to activate more to achieve the same than normally functioning regions. Also the atypical right hemispheric regions with reference to the abnormalities found by Sommer et al. and Foundas et al. Maybe it's the cause of unsucessful initiation?? Thus, unlike the cerebellar vermis and auditory regions, I am less convinced that it's only effect.

To finish off, a provacative thought: Is this the end of functional brain research on PDS using fMRI or PET? If all they say is true, it's unsucessful initiation that needs to be studied. This can only be done either by looking at structural difference or with a high temporal resolution (like MEEG, see for example Samelin et al. and Walls et al. )

In my next blog, I'll leave brain research behind and talk about the Oxford Disfluency Conference coming up in July.


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