IQ rises and falls during teenage years
Teenage years are all about changes in development, hormones and stress. But that is not all. New research from the United Kingdom shows how the intelligence quotient (IQ), a score generated from one of several different standardised tests designed to assess intelligence, can either significantly rise or fall during adolescence. These changes are linked with changes to the structure of the human brain. The findings, presented in the journal Nature, could impact the testing and streaming of children during their school years.
For the most part, people have always believed that our intellectual ability is a stable factor in our lives. IQ scores have long been used to predict children's educational achievement as well as their future employment prospects. But scientists at the Wellcome Trust Centre for Neuroimaging at University College London and the Development Neurocognition Laboratory at the University of London in the United Kingdom have observed how our IQ is not constant.
Led by Professor Cathy Price of the Wellcome Trust Centre for Neuroimaging, the researchers tested 33 subjects in 2004. These teenagers were all healthy and aged between 12 and 16 years. The subjects were re-tested in 2008, when they were 15 and 20 years old. For both test phases, the team used magnetic resonance imaging (MRI) to take structural brain scans of the teenagers.
Their findings show that IQ scores measured in the second test varied significantly from the test scores measured four years earlier. A number of participants had boosted their performance relative to similar-age peers by as much as 20 points on the standardised IQ scale. Other subjects reported a drop in performance by a similar amount.
The team also assessed the MRI scans to determine if there was a correlation with changes in the structure of the participants' brains. The result would help clarify if these changes were meaningful, according to the researchers.
'We found a considerable amount of change in how our subjects performed on the IQ tests in 2008 compared to four years earlier,' says lead author Sue Ramsden, also from the Wellcome Trust Centre for Neuroimaging. '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 verbal IQ of each participant was also measured; language, arithmetic, memory and general knowledge were included. For non-verbal IQ, the team asked the subjects to spot the missing elements of a picture or solve visual puzzles. The researchers identified a clear correlation with specific brain regions.
A higher verbal IQ score correlated with higher grey matter density in an area of the left motor cortex of the brain that is activated when articulating speech. A higher non-verbal IQ score correlated with higher grey matter in the anterior cerebellum that influences hand movements. But a higher verbal IQ does not correlate with a higher non-verbal IQ.
While there is no sure answer to why IQ changes and why the subjects' performance either improved or declined, the researchers suggest the differences are triggered by the participants' early or late development. Education could also impact a changing IQ, which in turn could affect how schoolchildren are assessed, according to the team.
'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,' Professor Prince says. '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.'
Commenting on the results of the study, Dr John Williams, head of Neuroscience and Mental Health at Wellcome Trust says: 'This interesting study highlights how 'plastic' the human brain is. 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.'
Data Source Provider: Nature; Wellcome Trust Centre for Neuroimaging
Document Reference: Ramsden, S., et al. (2011) 'Verbal and non-verbal intelligence changes in the teenage brain', Nature, published 19 October. DOI: 10.1038/nature10514.
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