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A first glimpse at healthy cognitive development

Yes, there are gender differences in cognitive function, but they're more limited than previously thought. And yes, income affects cognitive performance, but less than expected. And while cognitive skills steadily improve in middle childhood, they then seem to level off, calling into question the idea of a burst of brain development in adolescence.

These are the earliest findings of the large National Institutes of Health MRI Study of Normal Brain Development, a population-based study begun in 1999. The analysis, led by Deborah Waber, PhD, in Children's Hospital Boston's Department of Psychiatry, focused on cognition and behavior in 385 demographically diverse 6- to 18-year-olds at Children's and five other centers. Children with medical or psychiatric disorders (or risk factors for them) were excluded.

In this sample, boys performed better on tests of perceptual analysis, and girls on tests of processing speed, motor dexterity and, initially, verbal learning. Low-income children scored lower on reading comprehension and calculation tests, and had lower overall IQ scores. However, they matched their peers on basic cognitive tasks like word reading and memory, and their overall performance surpassed previously reported population averages.

Cognitive performance rose steadily in middle childhood, but leveled off at ages 10 to 12 on most tests, improving more slowly or not at all in adolescence. However, since these findings average a whole age group's performance at a single time point, Dr. Waber cautions that longitudinal data is needed. "We don't know whether everyone improves more slowly in adolescence, or whether some continue to improve while others don't," she notes. Dr. Waber's analysis was published May 18 by the Journal of the International Neuropsychological Society. Future studies will seek to correlate neuropsychiatric performance with findings on brain imaging.

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