By ROBIN MARANTZ HENIG
New York Times
August 18, 2010
...Neuroscientists once thought the brain stops growing shortly after puberty, but now they know it keeps maturing well into the 20s. This new understanding comes largely from a longitudinal study of brain development sponsored by the National Institute of Mental Health, which started following nearly 5,000 children at ages 3 to 16 (the average age at enrollment was about 10). The scientists found the children’s brains were not fully mature until at least 25. “In retrospect I wouldn’t call it shocking, but it was at the time,” Jay Giedd, the director of the study, told me. “The only people who got this right were the car-rental companies.” When the N.I.M.H. study began in 1991, Giedd said he and his colleagues expected to stop when the subjects turned 16. “We figured that by 16 their bodies were pretty big physically,” he said. But every time the children returned, their brains were found still to be changing. The scientists extended the end date of the study to age 18, then 20, then 22. The subjects’ brains were still changing even then. Tellingly, the most significant changes took place in the prefrontal cortex and cerebellum, the regions involved in emotional control and higher-order cognitive function.
As the brain matures, one thing that happens is the pruning of the synapses. Synaptic pruning does not occur willy-nilly; it depends largely on how any one brain pathway is used. By cutting off unused pathways, the brain eventually settles into a structure that’s most efficient for the owner of that brain, creating well-worn grooves for the pathways that person uses most. Synaptic pruning intensifies after rapid brain-cell proliferation during childhood and again in the period that encompasses adolescence and the 20s. It is the mechanism of “use it or lose it”: the brains we have are shaped largely in response to the demands made of them. ...
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