Stages in human brain development.

In a 1974 survey of data on human brain and head growth statistically significant peaks in growth rates of human brains were found around ages 11 years and 15 years. In addition, correlations were found in that almost all studies had non-significant peaks around ages 3, 7, 11-12 and 15 years; troughs were found at the intermediate ages (5, 9, and 13 years). More recent data include a very extensive collection of head circumference data from a dozen countries which showed statistically significant peaks around ages 7, 12, and 15 years. Confirmation of those results have been found in data on cortical thickness, photographs of neuronal arbors, and the percent of EEG energy found in the alpha-frequencies (8-13 cps). The proposed peak around age 3 years cannot be decided from existing brain weight and head circumference data bases, but the EEG data and the cortical thickness data supply significant support. Overall, there are statistically significant peaks in brain growth rates at age 7, 11-12, and 15 years, though the latter holds only for males at present. The significance of the stages for development of brain functions is being explored.