Contrary to expectations, some teenagers’ IQ scores changed significantly over a four-year period.
IQ volatility. I’m Bob Hirshon and this is Science Update.
It’s long been thought that your IQ doesn’t change much over time. But maybe not, according to cognitive neuroscientist Cathy Price of the Wellcome Trust Centre for Neuroimaging at University College London. She and her colleagues tested 33 healthy teenagers at age 14 and again at 18. Many of their IQ scores went significantly up or down—on the verbal or non-verbal subtest, or both.
And we were able to show that the degree to which their scores had changed over the four-year period matched the degree to which parts of their brain had changed.
Kids with better scores had somehow increased the density of nerve cells called grey matter—in brain areas that were relevant to the subtests they improved on. The next question is whether these changes were biologically pre-determined, or the result of the teenagers’ activities during the four-year gap. I’m Bob Hirshon for AAAS, the Science Society.
Making Sense of the Research
It's widely believed that I.Q. (a score on a test that measures certain basic intellectual skills) is more like your eye color than your ability to do math—in other words, that it reflects your inborn, natural intelligence rather than anything you've learned. That's partly because the IQ test is designed to test basic intellectual ability, not knowledge that you could have picked up from school or books. But more importantly, it's because the average IQ of a general population tends to remain close to the same over time.
However, this study looked at IQ on an individual level, over a very specific time period (the teenage years) during which the brain undergoes a lot of growth and development. They found that some of the volunteers' IQ scores rose or fell over a four-year period, by as much as 20 points—a significant change, given that 100 represents an average IQ score, and that 95% of people score in between 70 and 130.
Furthermore, the changes were often different in the two IQ sub-tests. One section, verbal IQ, evaluates language, basic math, and memory. The non-verbal section includes more abstract challenges, like visual puzzles. Volunteers who developed denser gray matter in their brains' left motor cortex, which is involved in producing speech, showed improvements on the verbal section. Improvement on the non-verbal section was associated with increased gray matter density in the anterior cerebellum, which controls the sense of our bodies in space.
The fact that IQ changes were linked to real changes in the structure of the brain suggests that the change in scores over time wasn't just a fluke—for example, a “good test day” versus a bad one. That's also supported by the fact that some volunteers showed improvement or decline in one subtest but not in others. One might expect that day-to-day variations in test-taking ability, like alertness or confidence levels, would affect the entire test, not just one section.
What isn't clear is whether these changes in IQ came from the volunteers' behavior during the four-year period, or whether these changes were biologically pre-determined. It's possible, for example, that some people's brains happen to develop faster in adolescence, even in particular regions, which might cause their IQ scores to go up over time. However, it's also possible that the volunteers' activities in their teenage years, including education, hobbies, nutrition, alcohol and drug consumption, and countless other factors, might have influenced their IQ for better or worse.
Now try and answer these questions:
- What has generally been believed about IQ scores over time?
- How did this study challenge that belief?
- Why is it significant that people's scores changed in different ways on different parts of the test?
- How did the IQ changes reflect brain changes? Why is this important?
- What does this research say about the common practice of “tracking” students by ability early in their school years?
You may want to check out the November 4, 2011, Science Update Podcast to hear further information about this Science Update and the other programs for that week. This podcast's topics include: A pacemaker that restarts the heart with light, and a secret code made from fluorescent bacteria. And, could a lack of outdoor activity be making kids more nearsighted? Also, new research suggests that IQ might not be as stable as once thought.
The Science Update Big Heads delves into the relationship between intelligence and brain size.
The Science Update lesson Big Heads delves into the relationship between intelligence and brain size.
To learn how behavior during the teen years can impact intelligence, try the Science NetLinks lesson Alcohol's Effect on the Mind and Body.