IQ and Brain Growth

One of the most hyped stories of the past few days has been that of how high IQ children's brains grow differently that those of average children.

The brains of highly intelligent children develop in a different pattern from those with more average abilities, researchers have found after analyzing a series of imaging scans collected over 17 years.

I think this is interesting, but a high degree of skepticism is probably appropriate. Like the liberal vs. conservative preschooler story of a week or so ago, this one has a narrow base:

The finding is based on 307 children in Bethesda, Md., an affluent suburb of Washington. Starting in 1989, they were given regular brain scans using magnetic resonance imaging, a project initiated by Dr. Judith Rapoport of the National Institute of Mental Health.

So what did they find:

This set of scans has been analyzed by Philip Shaw, Dr. Jay Giedd and others at the institute and at McGill University in Montreal. They looked at changes in the thickness of the cerebral cortex, the thin sheet of neurons that clads the outer surface of the brain and is the seat of many higher mental processes.

The general pattern of maturation, they report in Nature today, is that the cortex grows thicker as the child ages and then thins out. The cause of the changes is unknown, because the imaging process cannot see down to the level of individual neurons.

But basically the brain seems to be rewiring itself as it matures, with the thinning of the cortex reflecting a pruning of redundant connections.

The analysis was started to check out a finding by Dr. Thompson: that parts of the frontal lobe of the cortex are larger in people with high I.Q.'s. Looking at highly intelligent 7-year-olds, the researchers said they were surprised to find that the cortex was thinner than in a comparison group of children of average intelligence.

It was only in following the scans as the children grew older that the dynamism of the developing brain became evident. The researchers found that average children (I.Q. scores 83 to 108) reached a peak of cortical thickness at age 7 or 8. Highly intelligent children (121 to 149 in I.Q.) reached a peak thickness much later, at 13, followed by a more dynamic pruning process.

One interpretation, Dr. Rapoport said, is that the brains of highly intelligent children are more plastic or changeable, swinging through a higher trajectory of cortical thickening and thinning than occurs in average children. The scans show the "sculpturing or fine tuning of parts of the cortex which support higher level thought, and maybe this is happening more efficiently in the most intelligent children," Dr. Shaw said.

Another red flag was raised for me by this detail:

The I.Q. was tested when the children entered the program. Further tests were not needed because I.Q.'s are so stable, Dr. Rapoport said.

I have tremendous respect for Dr. Rapoport, but does this make sense? You study brain plasticity based on IQ but never recheck your baseline condition? And IQ test results are not *that* stable. I personally have a whole raft of scores spanning 50 points or so (not counting Dr. M's estimates, which would add another 40 points to the range). Besides, wouldn't it be interesting to compare any changes in brain development with measure IQ?

It is somewhat amusing in that it seems to turn a conventional idea upside down. Instead of your brain configuration determining your smarts, it seems to be more the other way around. If genes are everything, of course, there isn't any difference.