‘Teenagers’ IQ can rise and fall as they grow older’

Across our lifetime, our intellectual ability is considered to be stable, with IQ scores taken at one point in time used to predict educational achievement and employment prospects later in life.

However, in a study carried out by funded by the Wellcome Trust, researchers at the Wellcome Trust Centre for Neuroimaging at UCL (University College London) and the Centre for Educational Neuroscience, show for the first time that in fact our IQ is not constant.

The researchers 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).

IQ depends very much on the time that these tests are administered – Prof Cathy Price

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.

Comparing the 2008 and 2004 scores, some subjects had improved their performance relative to people of a similar age by as much as 20 points on the standardised IQ scale; in other cases, however, performance had fallen by a similar amount. In order to test whether these changes were meaningful, the researchers analysed the MRI scans to see if there was a correlation with changes in the structure of the subjects’ brains.

Prof Cathy Price, a cognitive neuroscientist from University College London (UCL) who lead the research, explained significance of the findings to Channel 4 News.

“What we’ve found is that some teenagers developed past what was expected of them and others fell back relative to their peers and this is expected in most school subjects. The IQ tests that we’re using are supposed to be a marker of intelligence, in fact what our results are showing is that it depends very much on the time that these tests are administered.”

She added: “Many people assume that intelligence at one age is going to be the same at another age in the same individual, and in fact, if you have a look at the whole group, their intelligence didn’t change from age 13-17: what you see is that individuals within the group are moving in different directions.”

Prof Price admitted that it is not clear why IQ should have changed so much and why some people’s performance improved whilst others’ decline.

“We don’t know what caused these changes. Either the changes in the brain caused the changes in the ability to learn or it could have been the act of learning changed the brain.”

But the findings may have implications for testing and streaming of children during their school years.

“It will be interesting to see whether structural changes as we grow and develop extend beyond IQ to other cognitive functions,” said Dr John Williams, Head of Neuroscience and Mental Health at the Wellcome Trust.

“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.”