Scientific Method / Science & Exploration

Teens’ IQs can rise (or fall), thanks to changes in the brain

During adolescence, changes in two regions of the brain have been linked to …

Here’s some good news for the parents of adolescents: if your teenager seems like a bit of a dud in the intelligence department, it’s possible that he or she isn’t doomed to a life of intellectual failure. On the flip side, however, kids who show early signs of high intelligence may not fare as well as you think they will. This information comes from a new study in Nature that shows that IQ is surprisingly variable during the teenage years, and that these changes are associated with specific changes in brain structure.

Over the course of the study, a group of 33 teenagers were given 2 IQ tests: one during early adolescence, and other in late adolescence. Both relied on the commonly used Weschsler intelligence tests. At the time of each IQ test, each teenager had a structural brain scan with an MRI machine. None of the participants knew they would be called back for a second test a few years later.

In each test, the subjects' IQ scores varied greatly, ranging from 77 to 135 during the first test, and 87 to 143 during the second. IQs are split into two types of scores: verbal IQ, which relates to verbal tasks, and performance IQ, which measures abilities such as logic and reasoning.

When called back for their second test, many of the subjects scored very differently on the IQ tests than they had the first time. Nearly 40 percent had different verbal IQ scores, and 21 percent had different performance IQ scores. Some teens scored lower and some scored higher than they had the first time; there was no correlation between the changes in verbal and performance IQ scores.

The researchers then compared these changes to differences between the two MRI scans for each subject. They found that the teens that had large changes in IQ scores between the two tests also had definite changes in their brain structure. Even more intriguingly, each type of score was related to changes in a different region.

Changes in verbal IQ were associated with changes in grey matter density in the left motor cortex, an area associated with speech. This area is activated by tasks such as reading and reciting numbers. Changes in performance IQ, on the other hand, were correlated with changes in grey matter density in the anterior cerebellum, which is responsible for hand movements. In the study, tasks that involve pressing a button activated this region of the brain.

From these results, it appears that very different types of IQ scores are closely linked to different sensorimotor skills. These abilities seem particularly apt to change over adolescence, as various structures in the brain develop. Densities of these brain regions could explain between 13 and 20 percent of the differences in the subsequent test scores, so clearly there must be other things going on.

Of course, IQ is just a number, and an individual's performance on a test can’t fully reflect their ability and potential. However, scientists still regard IQ scores as the best proxy we have for general intelligence. More research needs to be done to determine whether changes in these IQ scores are evident in other measures of performance, and whether they affect individuals’ education or employment history. Even more importantly, we don’t yet know why some teenagers' scores improved and others fell, so you can’t yet be sure what will happen to your children’s IQs as they pass through adolescence.

Nature, 2011. DOI: 10.1038/nature10514  (About DOIs).

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