A new study debunks traditional psychological theory by finding that Intelligence Quotient (IQ), the standard measure of intelligence, can increase or fall significantly during teenage years.

According to UK researchers, the shifts are associated with changes in brain structure. Researchers believe the findings may have implications for testing and streaming of children during their school years.

Traditional theory has assumed intellectual ability to be stable throughout the lifespan and that IQ scores taken at one point in time can be used to predict educational achievement and occupational matches in adulthood. The new study, published in the journal Nature, shows for the first time that IQ is not constant.

A research team lead by Cathy Price, Ph.D., Wellcome Trust’s Senior Research Fellow, tested 33 healthy adolescents in 2004 when they were between the ages of 12 and 16 years.

They then repeated the tests four years later when the same subjects were between 15 and 20 years old. On both occasions, the researchers took structural brains scans of the subjects using magnetic resonance imaging (MRI).

The investigators found significant changes in the IQ scores measured in 2008 compared to the 2004 scores.

Some subjects had improved their performance relative to people of a similar age by as much as 20 points on the standardized IQ scale; in other cases, however, performance had fallen by a similar amount.

In an effort to determine if the changes were meaningful, researchers analyzed the MRI scans to see if there was a correlation with changes in the structure of the subjects’ brains.

“We found a considerable amount of change in how our subjects performed on the IQ tests in 2008 compared to four years earlier,” said Sue Ramsden, Ph.D., first author of the study.

“Some subjects performed markedly better but some performed considerably worse. We found a clear correlation between this change in performance and changes in the structure of their brains and so can say with some certainty that these changes in IQ are real.”

The researchers measured each subject’s verbal IQ, which includes measurements of language, arithmetic, general knowledge and memory, and their nonverbal IQ, such as identifying the missing elements of a picture or solving visual puzzles.

The results clearly demonstrate that the changes in verbal IQ were associated with particular regions of the brain.

That is, an increase in verbal IQ score were related to an increase in the density of grey matter – the nerve cells where the processing takes place – in an area of the left motor cortex of the brain that is activated when articulating speech.

Similarly, an increase in nonverbal IQ score correlated with an increase in the density of grey matter in the anterior cerebellum, which is associated with movements of the hand. However, an increase in verbal IQ did not necessarily go hand-in-hand with an increase in nonverbal IQ.

According to Price, it is not clear why IQ should have changed so much and why some people’s performance improved while others’ declined. It is possible that the differences are due to some of the subjects being early or late developers, but it is equally possible that education played a role in changing IQ, and this has implications for how schoolchildren are assessed.

“We have a tendency to assess children and determine their course of education relatively early in life, but here we have shown that their intelligence is likely to be still developing,” said Price.

“We have to be careful not to write off poorer performers at an early stage when in fact their IQ may improve significantly given a few more years.

“It’s analogous to fitness. A teenager who is athletically fit at 14 could be less fit at 18 if they stopped exercising. Conversely, an unfit teenager can become much fitter with exercise.”

Other recent research supports the notion that brain structure remains “plastic” and malleable even throughout adult life. In an animal study, Price showed that guerrillas in Colombia who had learned to read as adults had a higher density of grey matter in several areas of the left hemisphere of the brain than those who had not learned to read.

In another study, Eleanor Maguire, Ph.D., showed that part of a brain structure called the hippocampus, which plays an important role in memory and navigation, has greater volume in licensed London taxi drivers.

“The question is, if our brain structure can change throughout our adult lives, can our IQ also change?” added Price. “My guess is yes. There is plenty of evidence to suggest that our brains can adapt and their structure changes, even in adulthood.”

The evolution of brain imaging has fueled an interest in learning how the brain may adapt or change over time.

“This interesting study highlights how plastic the human brain is,” said John Williams, Ph.D., head of neuroscience and mental health at the Wellcome Trust.

“It will be interesting to see whether structural changes as we grow and develop extend beyond IQ to other cognitive functions. This study challenges us to think about these observations and how they may be applied to gain insight into what might happen when individuals succumb to mental health disorders.”

Source: Wellcome Trust