Tangently related... This article, found in an old discussion link on the forum, also describes a connection between brain development and behavior (what some might call "personality").
http://www.nytimes.com/2012/05/13/m...ld-a-psychopath.html?pagewanted=all&_r=0 Can You Call a 9-Year-Old a Psychopath?
By Jennifer Kahn on May 11, 2012
The New York Times
Researchers hope, for example, that the capacity for empathy, which is controlled by specific parts of the brain, might still exist weakly in callous-unemotional children, and could be strengthened.
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Researchers have linked coldblooded behaviors to low levels of cortisol and below-normal function in the amygdala, the portion of the brain that processes fear and other aversive social emotions, like shame. The desire to avoid those unpleasant feelings, Waschbusch notes, is part of what motivates young children to behave. “Normally, when a 2-year-old pushes his baby sister, and his sister cries, and his parents scold him, those reactions make the kid feel uncomfortable,” Waschbusch continued. “And that discomfort keeps him from doing it again. The difference with the callous-unemotional kids is that they don’t feel uncomfortable. So they don’t develop the same aversion to punishment or to the experience of hurting someone.”
Waschbusch cited one study that compared the criminal records of 23-year-olds with their sensitivity to unpleasant stimuli at age 3. In that study, the 3-year-olds were played a simple tone, then exposed to a brief blast of unpleasant white noise. Though all the children developed the ability to anticipate the burst of noise, most of the toddlers who went on to become criminals as adults didn’t show the same signs of aversion — tensing or sweating — when the advance tone was played.
Fortunately the article contained hope in the sentence "Physiology isn’t destiny.”