Wednesday, November 14, 2007

cortex maturation: lag, span and thickness: ADHD, Schizophrenia, autism , IQ

There is an article making waves regarding the delayed maturation of the cortex of children with ADHD and so I thought I will throw in my two cents and try to simplify things.

First what is cortex maturation- the cortex of normal children first increases in size (as presumably new connections are made) , reaches a peak around 8 years of age and then the cortex thins (as spurious connections are pruned). We normally think of more connections being more beneficial, so it stands to reason why pruning should happen- but more connections do not translate into better connections- we only need to retain the right connections - the spurious connections need to be mercilessly pruned, if we are to function correctly. A theory based on this logic also asserts that we are born synaesthetes, but the spurious connections get pruned under normal development.

Now there are several things that can go wrong with this wiring and pruning process. Too much wiring can leave you with a thicker than normal cortex , too much pruning can leave you with lesser connections than required for normal functioning. Also the achievement of normal thickness, and subsequent thinnness can be developmentally shifted or lag from the normal developmental plan. Finally the thickening and thinnening may be squeezed in time and may happen at a faster rate for some individuals. Conversely, this may be spread over a broader time period and o9ccur at a relatively slower rate for other individuals. Considering the three factors of Size ( peak thichkness/ thinnness achieved), Lag (start and end of thickening and thinning process) and Rate (faster development over small time frame or longer span with slow rate of pruning/ initial connection formation) one gets 6 combinations (if we treat them as independent of each other) . Also considering that Thickening (initial connection formation) and Thinning (subsequent pruning) may also be independent one gets 12 combinations. these are sufficiently complex for me to abstain from making any sweeping generalizations. So I'll go to data:
1. In ADHD, new research (as also highlighted above) reveals, that the development (thickening and thinning ) of cortex is similar to normal individuals- only it is slightly shifted and starts later. this explains why ADHD disappears after teenage and is a problem only in childhood.

2. Children with higher IQ have faster rate of thickening and thinning of cortex as seen from graphic below.

3. Research from Paul Thomsaon's lab at UCLA has shown that in schizophrenia the normal pruning process does not stop in teenage as in normal adults, but continues beyond the early teenage resulting in more pruning than is normal.
4. I've read claims that in Autism the cortex is thicker and that it matures early. I'm tempted to posit Autism as a reverse trend of schizophrenic maturation, but need more accurate refernces and would be highly obliged if someone points me to appropriate resources.

All this seems very promising and I would be watching ne23s related to these developments more closely in future , considering that some of these are comorbid - like autism and IQ in high functioning ASDers and Creativity and Schizophrenia.

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