Brain researchers have found a significant correlation between early brain growth and intelligence.
Several studies in children have shown that those with larger brains, measured with imaging studies or as head circumference, tend to score higher on tests of cognitive function. Similar associations have been found in adults.
But this is predictive only in children and head size at birth is not as important as head growth during infancy
By the age of one, mean head circumference increased from 34.9cm at birth to 46.6cm.
Head growth after infancy was slower. Mean head circumference increased to 50.9cm by four years and to 53.4cm by eight years.
Average full-scale IQ was 106.3 at four years and 105.6 at eight years. The investigators report that only prenatal growth and growth during infancy were associated with later IQ.
At four years, after adjusting for parental factors, there was an average increase in full-scale IQ of 2.41 points for each one standard deviation increase in head circumference at birth and 1.97 points for each 1-SD increase in head growth during infancy.
This was conditional on head size at birth.
Head circumference at birth was no longer associated with IQ at eight years.
However, head growth during infancy remained significantly predictive, with full-scale IQ increasing an average of 1.56 points for each 1-SD increase in head growth.
Studies on adults to determine what factors influence intelligence are also ongoing at the MIND (Mental Illness and Neurodiscovery) Institute in Albuquerque. But it turns out, that just by looking at brains, you can tell nothing special.
When looking for creativity inside a human brain, the first thing you notice is -- nothing unusual.
Most scientists say that current brain imaging technology doesn't tell you much more.
"If I showed you two brains side by side, one with an IQ of 150, one with an IQ of 75, I can't tell the difference," says Jay Giedd of the National Institute of Mental Health, one of the most experienced researchers in the field.
How ever, scientists developing techniques that qualitatively analyze brain images are making more progress.
"We can make quantitative assessments of how much gray matter they have in every single area, and we can use that to predict what their IQ might be," Haier says. "This is in the very early stage, and I think this is going to be very interesting."
Dr. Rex Jung of the MIND Institute and Dr. Richard Haier of the University of California, Irvine, are using MRIs to measure various parts of the brain and what they find is pretty interesting.
So far, says Haier, he has found a strong correlation between intelligence and the size and shape of certain brain structures -- including parts of the superior parietal lobe (involved in sensory perception) and parts of the prefrontal cortex (associated with complex thinking, personality, planning, coordination).
Intelligence research is full of surprises. For example, the brains of smarter people, as measured by IQ, tend to be less active but more efficient, Haier says.
And, it seems, smart women are fundamentally different from smart men
...based on structural MRI scans that men and women think differently. For men in Haier's study, having more gray matter in certain areas corresponds to a higher IQ, while in women, it made no difference.
But with women, the amount of white matter in completely different areas is what corresponds to intelligence. (In both sexes, gray matter is made up of neurons that process information, while white matter is made of the neurons that connect different parts of the brain)....
"If a man and a woman both have a brain injury or a stroke at the same brain area, it could well be they have completely different effects," Haier says.
These conclusions, as you might guess, are controversial and have yet to be confirmed.
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