The study tested both the verbal (language, mathematics, memory and general knowledge) and non-verbal (puzzles and patterns) IQ of 33 children in 2004, then conducted the same testing in 2007 and 2008.

They found that in this period, the IQs of some children had risen or fallen by up to twenty points.

In order to find out why this happened, the researchers used an MRI to scan the brains of the different children. They found direct correlation between the changing densities of different parts of the brain and different types of intelligence.

They linked an increase in verbal intelligence with increased density of grey matter in the left motor cortex, involved in speech and vocabulary, and an increase in non-verbal intelligence with more grey matter in the anterior cerebellum, which helps us keep aware of our own bodies and their physical space.

Researcher from the study, Sue Ramsden, said the correlation between brain changes and IQ changes was clear in an ABC article.

"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," Ms Ramsden said.

[ABC]