A new study confirms what parents have long suspected: Adolescence can do a number on kids' brains. Researchers have found that IQ can rise or fall during the teen years and that the brain's structure reflects this uptick or decline. The result offers the first direct evidence that intelligence can change after early childhood and provides new hope for boosting the brain's abilities.
Although researchers debate what IQ tests actually measure , they agree that scores can predict our ability to learn and perform certain tasks, and to some degree forecast our later academic achievement and job performance. Scores have long been thought to stay relatively stable throughout our lives; the few studies that have shown some variation in IQ could not rule out measurement errors or differences in testing environment as the cause.
So neuroscientist Cathy Price of University College London and colleagues looked beyond the scores. They tested 33 teenagers—19 boys and 14 girls—in 2004, when they were 12 to 16 years old, and again in 2008, when they were 15 to 20 years old. Each time, the teens took IQ tests that measured their verbal and nonverbal abilities. Then, using magnetic resonance imaging, the researchers scanned the teenagers' brains while they performed verbal tasks, such as reading or naming objects, and nonverbal tasks, such as solving visual puzzles with their hands. The idea was to match their test scores with a picture of their brain's structure and activity at each time.
The test results revealed dramatic changes: between their first testing and their second, the teens' verbal and nonverbal IQ scores rose or fell by as many as 20 points  (on a scale for which the average is 100). Some teens improved or declined in just their verbal or nonverbal skills or improved in one area and declined in the other.
The brain scans mirrored the score differences. In teens whose verbal IQ scores had increased, for example, the scans showed increased gray matter density in a region of the brain activated by speech. Teens whose nonverbal skills had improved showed changes in a brain region associated with motor movements of the hand.
"These changes are real and they are reflected in the brain," says Price, whose team reports the finding online today in Nature. "People's attitude is to decide early on that this is a clever kid, and this is not a clever kid—but this suggests you can't make that assessment in the teenage years."
The results are "really exciting," says John Gabrieli, a neuroscientist at the Massachusetts Institute of Technology in Cambridge, who was not involved in the study. "People have thought IQ is fixed or that it becomes stable very early in life, but here is meaningful evidence that variation happens and continues well into adolescence."
The study offers no clues to why the fluctuations occur. But it does raise the possibility that training or other interventions could boost performance, says Frances Jensen, a neurologist and neuroscientist at Harvard Medical School and Children's Hospital Boston."This is a really nice mixed message for teens," she says. "It suggests there's still plasticity at this stage ... so you can still work on weaknesses and enhance strengths."
Jensen notes the study has another potentially powerful implication: Although teen angst and eye rolling may fade with time, the brain's ability to boost—or lose—its brainpower may not. "Is the end of the story in the teen years, or is there still this plasticity in the young adult brain and beyond?" she says. "I don't think we know that yet."