Thursday, September 10, 2009

Structural Abnormalities: the result or consequence

When diffusion tensor imaging data (see the latest fiber tracking imaging data) came out to show that stutterers show abnormalities in speech related areas of the left brain, the case for stuttering having a neurobiological basis has strengthened. However, many have put forward the argument that these abnormalities are the result of stuttering (like the apparent finding of an increased spatial memory area of London taxi drivers). Many unfortunately did not come up with argument by good scientific thinking but as an intellectual knee-jerk reaction in defense of their ideology "it is is all psychological". Here is their argument: we stutter due to psychological issues, the brain shows abnormalities, they cannot be due to a neurological issue, so they must be the result of stuttering.

Nevertheless the argument itself deserves attention. Here is my opinion:

1. It is not yes or no situation. A stuttering adult might well have abnormalities due to a neurological issues and due to long-term stuttering.

2. The taxi driver example is not really comparable, because their functional data shows NOT abnormally! They still activate their brain in exactly the same way as normal drivers, but their activated area of spatial memory is just bigger! Stuttering is very different in that we also activate different regions.

3. Many stutters show a significant genetic influences. So how do those genes act to create stuttering? They must be doing something. It is most likely that they are mutations that cause trouble in the development of a stable speech system, therefore showing up as structural abnormalities.

4. Kids also show abnormalities making it less likely to be only a consequence of stuttering.

5. Even recovered kids in adulthood show differences. As they recovered soon after onset, their brain show not have been shaped too much. It is more likely that they had and still have a structural abnormality and that just compensated for it.

1 comment:

Jo said...

Reading this post, and considering my own experiences recently; it makes me think that maybe the swathes of finger-pointing that stammering is a psychological issue and not neurological is due to the uncertainties many neurologists have in pinpointing the problem.

That it's simply easier to pass the buck and let it be someone else's problem. In this case sliding the problem over to psychologists.

Or am I just being cynical?!

Nowhere near as scientific, but valid in its own way - here's my evidence for this claim! (Neurology appointment – Take 2