Parents, you may be onto something: a small new study suggests that teens' intelligence, as measured by the IQ test, may fluctuate throughout adolescence.
The changes - in both verbal and nonverbal IQ - ranged as much as 20 points and were correlated with specific brain areas.
IQ has long been thought to remain stable over a person's lifetime.
The new findings might have implications for kids' educations, the researchers said, because they suggest that children, especially those with lower IQs, should not be pigeonholed into specific educational and career trajectories based on their IQ alone.
"Approximately one-fifth of our sample had very substantial changes, such that they moved from above average to below average or vice versa," said Cathy Price, senior study author and professor at the Wellcome Trust Centre for Neuroimaging, University College London, UK. The findings are published in the journal Nature.
According to the study authors, prior studies have shown changes in IQ in individuals over time, but those studies hadn't been able to rule out the possibility of chance.
In their research, Price and her colleagues measured the IQs of 33 individuals aged 12 to 16 in 2004. They performed MRI brain imaging of the adolescents' brains at the same time.
Four years later, the same group of individuals, now between 15 and 20 years old, were tested and underwent additional MRI scans.
The team report that changes in IQ did seem to occur, with some participants improving their scores by as much as 20 points over time, relative to people of similar age, while other kids saw declines in IQ levels.
"A change in 20 points is a huge difference," Price said in a statement to the media. For example, she said, "if an individual moved from an IQ of 110 to an IQ of 130 they move from being 'average' to 'gifted'." And if they moved from 104 to 84 they move from being high average to below average.
According to Price, that could have implications for adolescents' education, since it suggests that intellectual ability changes over time.
The fluctuations seemed correlated to changes in certain brain areas, with verbal IQ (such as might be used in language and maths) corresponding to a different part of the brain than non-verbal changes (involving visual questions).
Intelligence not 'fixed'
In the media statement, Price explained that "the degree to which verbal IQ changed correlated with the degree to which brain structure changed in an area of the brain that we are referring to as a 'motor speech area." She added that this region, the brain's left motor cortex, "is very active when we (including the participants in our study) articulate speech."
Nonverbal performance correlated to changes in the anterior cerebellum, which is also activated when making hand movements, Price noted.
The authors don't know yet what is driving these variations in IQ over time.
"It could either be an active environmental effect (such as education/learning ) or it could relate to developmental differences (late developers/early developers) or it could be both," Price said in an interview. "This is the classic nature/nurture debate. I am pretty sure that there is a strong environmental effect because we know that the adult brain changes with learning. In this case, intensive training causes brain changes."
The take-home message, according to one expert, is that intelligence may not be as "fixed" in adolescence as once thought.
Brain amenable to change
"The brain is clearly, at least in the teenage years, more plastic and amenable to change," said Paul Sanberg, distinguished professor of neurosurgery and director of the University of South Florida Center for Aging and Brain Repair in Tampa. "The real question is, does this continue into adulthood? Is this reflective of changes we now see in plasticity in the brain in adulthood? The data is suggesting that things can get better."
Price hasn't yet measured whether or not IQ changes in adults, "but my guess would be yes, because intensive skill training in adults causes brain changes."
However, another expert cautioned that the study did have some limitations. Michael Carey is an assistant professor of psychiatry and behavioral science at Texas A&M Health Science Center College of Medicine.
He believes that some of the IQ tests used in the study were outdated, nor did they take into account other factors, such as age, gender or whether a person is right-handed or left-handed when identifying brain structures related to the change.
"It's a relatively small sample and pretty selective. The average IQs are above average, even though there's a lot of variation," said Carey, who is also a psychologist with Scott & White, in Temple. "The question is, how representative is this of natural day-to-day adolescence?"
Find out more on the developing brain at the US National Institute of Mental Health.
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