Intelligence, as measured by Intelligence Quotient (IQ), can rise or fall significantly during our teenage years, and these changes are accompanied by changes in brain structure, according to new research published in the journal Nature that suggests the findings may have implications for the way children are tested and streamed at school.
The news will come as a great surprise to many scientists, because for years there has been a belief that IQ remains stable throughout life: and indeed many have used early IQ to predict subsequent educational achievement and employment prospects.
But this new study, funded by the Wellcome Trust and conducted at the Wellcome Trust Centre for Neuroimaging at UCL (University College London), has evidence that challenges this view.
Led by Wellcome Trust Senior Research Fellow Professor Cathy Price, the UCL researchers tested 33 healthy adolescents in 2004 when they were aged between 12 and 16, and then repeated the tests 4 years later, when they were between 15 and 20.
At both times, the youngsters completed IQ tests and underwent structural brain scans using magnetic resonance imaging (MRI).
When they compared the results from 2008 to 2004, the researchers found significant differences in IQ scores. For some it had gone up, for others it had gone down, compared to others of a similar age. And the changes were significant, varying by as much as 20 points on the IQ scale.
The researchers also found that these changes correlated to changes in brain structure as shown in the MRI scans.
“A combination of structural and functional imaging showed that verbal IQ changed with grey matter in a region that was activated by speech, whereas non-verbal IQ changed with grey matter in a region that was activated by finger movements,” write Price and colleagues adding that:
“By using longitudinal assessments of the same individuals, we obviated the many sources of variation in brain structure that confound cross-sectional studies.”
First author Sue Ramsden told the press:
“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.”
Verbal IQ measures language, arithmetic, general knowledge and memory ability, while non-verbal IQ assesses abilities like being able to spot what is missing in a picture or solve visual puzzles.
When they compared the two measures, the researchers found that an increase in verbal IQ was not necessarily accompanied by an increase in non-verbal IQ.
They write that these findings allow them to “dissociate neural markers for the two types of IQ and to show that general verbal and non-verbal abilities are closely linked to the sensorimotor skills involved in learning”.
These findings show that a young person’s intellectual capacity can go up or down, relative to his or her peers, conclude the researchers, pointing out, however, that while they offer encouragement to those whose potential may yet improve, they serve as a warning in that early achievers may not maintain their potential.
Price said it was not clear why IQ should have changed so much: why did some of the participants’ performance go up while others went down?
Perhaps it is because some of them were early and others were late developers, but another explanation could be the education they received, and this would have implications for the way we assess children in schools, she added.
“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,” explained 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.”
Price said it is like fitness. Teenagers who are as fit as athletes at 14 may be less fit at 18 if they don’t keep up their training, and conversely, unfit teenagers can become fitter with training.
Price and others with the Wellcome Trust have found evidence in other studies that show our brains can remain “plastic”, that is where the structure can change, throughout adulthood too, with changes coinciding with periods of intense learning, such as when adults learn to read, or when taxi drivers absorb a lot of navigational knowledge.
“There is plenty of evidence to suggest that our brains can adapt and their structure changes, even in adulthood,” said Price, who also believes the same applies to IQ.
Dr John Williams, Head of Neuroscience and Mental Health at the Wellcome Trust said the study shows just how “plastic” the human brain is, and that it will be “interesting to see whether structural changes as we grow and develop extend beyond IQ to other cognitive functions”.
The study also helps us think differently about what might be happening when people have mental health disorders, he added.
Written by Catharine Paddock PhD