New Delhi, Oct. 19: Intelligence quotient (IQ) levels of teenagers may rise or fall with corresponding changes in their brain structures, says a new research study that appears to question the reliability of IQ tests in early teenage years.

Neuroscientists in the UK have shown that IQ changes in teenagers correspond with changes in grey matter density in brain regions involved in specific intellectual abilities. Their study challenges the long-standing, yet debated, idea that IQ levels are constant throughout the lifetime.

The researchers have said their findings may be encouraging to those in their early teens who may be struggling in school but may be a warning to young high achievers. The study's results will appear in the journal Nature on Thursday.

“IQ changes – therefore, it does not measure a capacity to do well, it measures how well an individual is doing at a fixed time,” said Cathy Price, a professor at the Wellcome Trust Centre for Neuroimaging, University College London, and principal investigator in the study.

An Indian scientist, who specialises in the biological roots of cognition and education and was not associated with the British study, said its findings provide fresh evidence for the adaptability of the cognitive system and the poor reliability of IQ in assessing individuals.

“It is not a good idea to rely on IQ reports for the choice of a career or future studies,” said G. Nagarajuna, a research scientist at the Homi Bhabha Centre for Science Education, Mumbai.

Price and her colleagues gave 33 teenage volunteers standardised IQ tests twice, the first test when they were between 12 and 16 years old, and the second test three or four years later when they were between 15 and 20 years old.

They found that one in five teenagers showed significant changes in IQ. The scientists then used magnetic resonance imaging (MRI) scans to determine whether the observed changes in IQ were reflected in the teenagers’ brains.

Among those whose overall IQ scores changed, the highest rise was 21 points and the greatest fall was 18 points. In verbal IQ tests of vocabulary, arithmetic and information comprehension, the IQ changes ranged from a 20-point loss to a 23-point gain.

In non-verbal IQ tests that assessed picture completion, digit symbol coding, and picture arrangement tasks, the fluctuations ranged from a loss of 18 points to a gain of 17 points.

“Such large fluctuations in IQ were surprising,” said Sue Ramsden, a researcher at the University College London, and the study’s first author. Such changes previously observed were dismissed as measurement errors. “Our study shows they have a real basis in brain structure,” Ramsden told The Telegraph.

The MRI scans revealed a strong positive correlation between verbal IQ and changes in grey matter density in a brain's left motor cortex region that is activated by the articulation of speech. Non-verbal IQ correlated with grey matter density in the anterior cerebellum involved in motor movements.

The rise and fall in IQ was seen in people with high as well as low initial IQ scores. The results imply that early high performers will not necessarily excel, while a late achiever can catch up. “Some high performers got even better, some low performers got even worse,” Price said.

The study was not designed to determine whether the observed changes in the brain led to the IQ changes or improved performance caused the brain changes. “This is the classic nature or nurture debate,” Price said in an email interview. “But we do know that in adults, intensive training can result in structural changes in the brain. It is, therefore, possible that education, or a passion for a subject may have contributed to the observed changes.”

While this study did not examine IQ in adults, Price said she believes that verbal and non-verbal skills could also change in adulthood with similar effects on the brain structure. “The differences are likely to be smaller as the brain is not learning or changing as much in adulthood,” she said. “The teenage years are, or should be, a time of intense learning.”