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The size of your brain doesn't necessarily determine how smart you are. Brain researchers say how your brain thickens and thins when you're a kid has a bigger influence on your IQ. This ScienCentral News video has more.
Peaking Intelligence
A big brain doesn't necessarily mean you'll be the smartest in the class.
"Brainy kids aren't brainy just because they have more grey matter," says brain researcher Philip Shaw, of the National Institute of Mental Health (NIMH), referring to the kinds of cells that make up part of the brain. "I think that's part of the story, but not all of it. Rather, intelligence is related to the dynamics of how the brain grows."
Shaw and his research team found that children who scored highest on IQ tests had a distinctive pattern of brain growth. They used MRI brain scans to follow the development of the brains of 307 children from age seven to their late teens. While they found no difference in the kids' brain size by late adolescence, those with the highest IQ scores actually started out with a thinner than average cortex -- the outer layer of the brain that helps us reason and make decisions.
"The really highly intelligent children, they started off with a very thin cortex, it got thicker very quickly, peaked, and then also got thinner very quickly," Shaw explains. "Average intelligence children showed the same sort of pattern, but all the changes happen much more slowly. There was a very slow increase and a very slow decrease, and they also reached their peak cortical thickness a couple of years before the very intelligent children."
Shaw says that the thickening and thinning the researchers saw is only a matter of about half a centimeter in thickness, nevertheless, "In terms of what's happening in the brain that's really quite huge," he says. But by late adolescence they found no significant difference in the kids' cortex thickness.
The cortex is thought to control things like complex reasoning, memory and emotion. And although the thickening happens to some extent throughout the cortex, it is most pronounced in the front of the brain. "The frontal cortex is the bit of the brain that is thought to be the seat of abstract reasoning, planning and other complex thought activities," he explains.
The NIMH researchers, in collaboration with researchers at the Montreal Neurological Institute at McGill University in Canada, used standard intelligence tests known as the Wechsler Intelligence Scale for Children, appropriate to each age group. They test verbal knowledge, the meaning of words and the ability to detect patterns between certain words, among other things. "Although things like this sound very simple, they're actually the fundamental, basic building blocks of a lot our very complex brain activities," explains Shaw. "So the tests we use, I think, they relate well to how a child does in school and to some extent to how well a child will go on to do in terms of their occupation."
But he stresses that although IQ tests are reliable at measuring a child's intelligence, it's only one part of what makes a child who he or she is. It doesn't capture lots of other things about children, like their emotional wellbeing or their social wellbeing.
image: National Institute of Mental Health
And they don't yet know what's happening in the brain during this thickening and thinning, or why it happens differently from child to child. Shaw says that genes have a big influence, but that our interactions with the world around us also play a critical role. He notes that animal and human studies have shown that brain development involves not just the growth of brain cells and connections, but also the pruning of unneeded ones. "I think that its possible that in the most intelligent children the process of pruning or killing of brain cells that aren't being used is particularly efficient, and that's why they get thinner quicker," he says. "But that's only a possibility and we don't really know yet."
Shaw says learning how the brain develops in happy, healthy kids may help them to understand the brain patterns in kids with emotional and psychological difficulties. "All the children in this study were very happy, healthy children, so we get a good idea of the variation there is in brain development in a very healthy population," he explains.
He adds that a brain scan can't predict a child's intelligence, but attentive parents and teachers may help shape it.
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