IQ scores can increase or fall significantly during a person’s teenage years, and these changes are associated with changes in the brain's structure, according to a study published in the Oct. 20 issue of the journal Nature.
Intellectual ability, measured by IQ scores, had been considered to be stable across a person’s lifetime, with scores taken at one point used to predict educational achievement and employment prospects later in life. The findings of this latest study, which show for the first time that IQ is not constant, may have implications for testing and streaming of children during their school years.
Lead researcher, Professor Cathy Price, of the Wellcome Trust Centre for Neuroimaging, University College London, and colleagues tested 33 healthy adolescents between the ages of 12 and 16 years old in 2004. Tests were repeated when subjects were between 15 and 20 years old and on both occasions, researchers took structural brain scans using MRI.
Price and colleagues 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. The researchers analyzed the MRI scans to see if there was a correlation with changes in the structure of the subjects' brains.
“A combination of structural and functional imaging showed that verbal IQ changed with gray matter in a region that was activated by speech, whereas non-verbal IQ changed with gray matter in a region that was activated by finger movements,” wrote the authors.
The researchers measured each subject’s verbal IQ, which includes measurements of language, arithmetic, general knowledge and memory, and their non-verbal IQ, such as identifying the missing elements of a picture or solving visual puzzles. “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," Sue Ramsden, research assistant at Wellcome Trust Centre for Neuroimaging, said in a statement.
An increase in verbal IQ did not necessarily go hand-in-hand with an increase in non-verbal IQ, according to the researchers.
Price said it is not clear why IQ changed so much and why some people's performance improved while others declined. It is possible that the differences are due to some 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.”
Other studies from the Wellcome Trust Centre for Neuroimaging and other research groups have provided strong evidence that the structure of the brain remains 'plastic' even throughout adult life. For example, Price showed recently that guerrillas in Columbia who had learned to read as adults had a higher density of gray matter in several areas of the left hemisphere of the brain than those who had not learned to read. Professor Eleanor Maguire, also from the Wellcome Trust Centre, showed that the hippocampus, which plays an important role in memory and navigation, has greater volume in licensed London taxi drivers.
“This would be encouraging to those whose intellectual potential may improve, and would be a warning that early achievers may not maintain their potential,” wrote the authors.