Science Interviews

When Size Doesn't Matter

Dr Philip Shaw, US National Institute of Mental Health

Chris - Now people often seem to be undecided when it comes to whether size is important. But in the case of the developing human brain, it looks like brighter children, with higher IQs, are that way inclined because their brains are better at re-organising themselves. Philip Shaw, from the US National Institute of Mental Health in Washington DC, has brain scanned large numbers of children over the course of their development and also measured their IQs. Intriguingly, the most intelligent children often started with the least grey matter but also showed the greatest rate of structural changes in different parts of the brain.

Philip - Basically in this study we asked 'do children's brains develop differently according to how clever they are'? I think the key finding was that the smartest kids differed in how fast the thinking part of their brain changes as they grow up. So in the cleverer children, the cortex or the outer crust of the brain thickens more rapidly and for a longer period of time and then thins faster as well. So I think the main message was that brainy children aren't cleverer because they have more grey matter or more brain at any one age. Instead it's that intelligence is related to the way in which the cortex matures. So children who have very flexible or agile minds also seem to have a very flexible and agile cortex.

Chris - You did this using brain scans didn't you?

Philip - Yes. We worked with people from the Montreal Neurological Institute and we imaged 300 healthy children from about the age of six to the age of twenty. We imaged the majority of them more than once. The children were scanned roughly two or three times at two-yearly intervals and everyone also did an IQ test. This is a standard test which measures verbal and non-verbal knowledge and reasoning. We then split everyone into three groups on the basis of their IQ scores and then compared these three groups and saw how their cortex developed as they grew up.

Chris - Were there any regional differences in different parts of the brain in different individuals at different times?

Philip - Yes we found that the different patterns of growth most marked in the pre-frontal are the front bits of the cortex. That's the part of the brain that we think is the seat of reasoning, planning and other very complex thought functions. What think that the later peak thickness which we find in the pre-frontal cortex in children who are the most intelligent might reflect an extended period for the development of brain circuits, which can support very complex thinking.

Chris - What are the big unanswered questions that this has opened up?

Philip - I think one question is what's the role played by genetic factors. The parts of the brain that differed most according to intelligence overlapped to some degree with brain regions that are thought to be under the tightest genetic control. However I think that what exactly is inherited is unclear. Some researchers suggest that it's the way the child interacts with the environment that's inherited. So a clever child might have genes which incline him or her to evoke a very stimulating environment. The rich and varied experience the child has may then mould and sculpt the brain particularly efficiently.

Chris - So it would be quite interesting actually to follow these on and then subject their own children to the same analysis and see if they develop the same way.

Philip - Yes it would. I think other possibilities would be environmental enrichment in terms of education or working with families. Does this have an impact on how the cortex develops?

April 2006