An investigation into the link between intelligence and brain development, rare in its use of a longitudinal methodology and large sample size, has found superior intelligence is associated with particularly dynamic developmental changes to the cortex – rapid cortical thickening during childhood, followed by a period of marked pruning during adolescence.
“’Brainy children’ are not cleverer solely by virtue of having more or less grey matter at any one age,” the researchers said. “Rather, IQ is related to the dynamic properties of cortical maturation”.
Philip Shaw and colleagues at the National Institute of Mental Health in America divided 307 participants aged between 3 and 25 years into three groups – average, high and superior intelligence – based on their scores on age-appropriate IQ tests. Over half the sample had at least two brain scans, 30 per cent had three or more scans.
They found the frontal cortex of participants with ‘superior’ intelligence started off thinner than in ‘high’ and ‘average’ intelligence participants, but thickened rapidly until the age of 11 years, at which stage rapid thinning occurred. By contrast, the cortex of the high and average intelligence participants thickened more slowly until the age of about 7 or 8 years, followed by a period of less marked thinning than in the superior intelligence participants.
“The prolonged phase of prefrontal cortical gain in the most intelligent might afford an even more extended ‘critical’ period for the development of high-level cognitive cortical circuits”, the researchers said.
Shaw, P., Greenstein, D., Lerch, J., Clasen, L., Lenroot, R., Gogtay, N., Evans, A., Rapoport, J. & Giedd, J. (2006). Intellectual ability and cortical development in children and adolescents. Nature, 440, 676-679.