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How Teens Get That Way

June 06, 2004

Finally, a light at the end of childhood.

Researchers at the National Institute of Mental Health and UCLA have been exploring how human minds mature, when they do. It's tricky enough just to live this journey, let alone to track it medically for 17 years. The researchers found that parts of the brain's 100 billion neurons matured at different times.

This makes intuitive sense to parents, who've watched their babies progress from babbling infants to inquisitive toddlers to rambunctious kindergartners to chaotic grade-schoolers. Then come the high school years, which are hard to describe in a family newspaper. Parents witness their beloved's little mind expand, watching oral eloquence, visual acuity and coordination evolve for years. This makes a long series of challenges for adults raising future adults.

The researchers also found, however, that the mental neighborhood responsible for reasoning was the last to mature. Eureka! This explains age 15.

At that point, or slightly before, parents observe a vast void developing within the thickening skull of their new teenager, as if the brain were shrinking. The inner space seems to contain vast galactic clouds of behavioral gas swirling in unpredictable cyclones of emotion and hormones, producing pouts and worse. Communicating across this void of reason can involve lapses in time and patience requiring louder repeat transmissions. C'mere. Come here! Come here!

These scientists, all of whom presumably experienced teendom, periodically scanned 13 youngsters' brains from 4 to 21. Assembling composite time-lapse images of brain growth, they saw that front and back brain areas matured first; these process basic functions like smell, hearing and sight. Next came the brain's uptown, governing touch and movement. Then the parietal lobes, controlling language and spatial orientation. Finally came the most complex mental arena, the prefrontal cortex, which integrates the senses with sophistication and (tah dah!) reasoning.

Reasoning is last to develop. In late teens. This explains everything.

Researchers long knew that babies arrived with vastly more gray matter than necessary. As a result, billions of baby brain neurons die and fade away during early years; use it or lose it. What scientists just discovered was a second era of brain decay just before reasoning develops. Now we're getting warm. This explains that galactic void at 13; new teens can't yet use it, so they lose it. The brain doesn't seem to be shrinking. It is.

Such data help decode the mysteries of brain diseases like schizophrenia and autism. More immediately, as an explanation for inexplicable behavior, these findings may help parental brains mature, enhancing the patience lobe and shrinking the exasperation sector, causing adult eyes to roll less.

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