The brain's cortex matures faster in intelligent kids
Years ago, many educated people attributed differences in intelligence to brain size differences (such that if you were smarter, your brain would be bigger, and if you were dumber, your brain would be smaller). This sort of thinking led to amusing speculations of what future human beings might look like (I recall a childhood atlas showing an image of a bald future person with a huge head, but cannot find an image to point to), but was ultimately debunked when it became clear that actual skull volume had little relationship with intelligence. Scientific advances, both in terms of technologies like MRI scanning, and in our understanding of how the brain works, have helped to further refine our understanding. This latest study, which will appear in the March 30, 2006 issue of Nature, achieved using repeated MRI scans on children at different times during their growth, suggests that what separates more intelligent people from others is not the brain's total size or even the total size of the "thinking/verbal" part of the brain (the brain's outer cortex), but is instead the rate at which the cortex grows during childhood. According to the press release:
"Magnetic resonance imaging (MRI) scans showed that (more intelligent childrens') brain’s outer mantle, or cortex, thickens more rapidly during childhood, reaching its peak later than in their peers — perhaps reflecting a longer developmental window for high-level thinking circuitry. It also thins faster during the late teens, likely due to the withering of unused neural connections as the brain streamlines its operations."
The brain is NOT fully formed at birth. Instead, it is one of the last organs in the body to mature. It takes all the years of childhood and a portion of adolescence before it has completed its growing. Though science knows quite a bit about how individual things like genetics, nurturing environments, toxic exposures and viruses and the like can affect the growing brain, it is still not very clear how these various elements combine to influence each other and the growing brain. Which is to say - it isn't clear how locked into a particular rate of growth the brain is at birth. There are certainly opportunities to maximize the growth that is possible, and there may even be opportunities to push at the limits otherwise imposed by genetics.