In the Child Psychiatry Branch cohort noted above, total cerebral volume follows an inverted U shaped trajectory peaking at age 10.5 in girls and 14.5 in boys (Lenroot et al., 2007). In both males and females, the brain is already at 95% of its peak size by age 6 (Figure 1A). Across these ages, the group average brain size for males is ~10% larger than for females. This 10% differences is consistent with a vast adult neuroimaging and postmortem study literature but is often explained as being related to the larger body size of males. However, in our pediatric subjects the boys’ bodies are not larger than girls’ until after puberty. Further evidence that brain size is not tightly linked to body size is the fundamental decoupling of brain and body size maturational trajectories, with body size increasing through approximately age 17.
