Intelligence Quotient, or IQ tests have long been both a critical tool and a hot-button issue in the education field. Educators find the measures useful, in part because of their general stability: IQ scores tend to remain the same over the course of people's lives. Yet a new brain-imaging study published this afternoon in the journal Nature finds that during adolescence, a fifth of children can gain or lose as many as 20 points in IQ, suggesting that the score may be less reliable at the same time it is likely being used to make educational decisions about a student.
Researchers at the Center for Educational Neuroscience and the Wellcome Trust Center of Neuroimaging at the University College London, both in the United Kingdom, tested 33 normal children, first between the ages of 12 and 16, and then again four years later, using both IQ tests and functional magnetic resonance imaging, or fMRI, which measures blood flow in the brain.
The IQ score range is typically set by the average of scores within an age group on a series of standardized tests of various facets of intelligence, with the mean score set to 100 points and standard deviations set at 15-point increments. The researchers, led by Cathy J. Price, a Wellcome Trust senior research fellow, tested both the students' verbal IQ, measured by language, arithmetic, general knowledge and memory tests, and nonverbal IQ, measured by solving visual puzzles. They found that more than one in five students showed dramatic fluctuations in IQ over the course of their adolescence: Scores fluctuated from a decrease of 20 points to an increase of 23 points in verbal IQ and from a decrease of 18 points to an increase of 17 points in nonverbal IQ—in both cases more than a full standard deviation.
"Our results show that 'intelligence,' as measured by IQ tests, is still emerging in the teenage years," said Sue Ramsden, study co-author, in an email. "A change in 20 points is a huge difference. 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.
"If we had just observed changes in IQ scores over time, this might have been explained by the fact that there was just random variation in performance on tests, perhaps due to mood or concentration on the day or other factors," Ramsden said, "but the fact that those changes in measured IQ correlated with changes in brain structure in areas of the brain that are plausibly linked to the skills being tested indicates that the performance changes are genuine."
Researchers found children who had an increase in verbal IQ during adolescence also had an increase in the density and volume of gray matter in the brain's left motor cortex, an area associated with articulating speech. Those who had an increase in nonverbal IQ showed an increase in gray matter in the brain's anterior cerebellum, which is associated with finger movements. What's more, changes were independent of one another; generally, someone who had an increase in verbal IQ had a stable or decreased nonverbal IQ, and vice versa.
The study doesn't resolve the question of how much of intelligence is inherited versus gained through experience—a debate that flared in education circles after the 1994 publication of The Bell Curve which posited that IQ was fixed and genetic. "Generally, it's not clear what [the brain changes] are caused by. It could be caused by developmental delays in how the brain is growing and developing these skills ... or, alternatively, it could be related to the education," Price told me.
She likened the brain changes to changes in a child's physical fitness over the teenage years; a couch-potato kid may join a sports team and be athletic several years later, while a fit child who doesn't exercise may find herself unable to manage a strenuous hike several years later. "We know people who are fit at age 13 may also still be fit at age 18, but that's not necessarily the case. What you do with your body affects the body itself, and how the body is, affects your opportunities to do things in physical ways."
Yet Ramsden said the results should make educators think twice about how much stock to put in a student's potential deficits or strengths during the teenage years. "The teenage years are (or should be) a time of intense learning," she said. "The results indicate that an early developer doesn't necessarily continue to excel; and a late developer can catch up.
"Educators already know this," Ramsden said. "The more relevant point is that, if IQ changes are real (as we claim), they are not measuring a capacity to do well. They are measuring how well the individual is doing at a fixed time. If a teenager has poor nonverbal skills, this doesn't mean that they don't have the potential to improve these skills. Likewise, if a teenager has good nonverbal skills this does not mean that they will maintain these skills without practice."