Data taken from the Child Psychiatry Branch (CPB) cohort has shown several striking findings. One is the degree of variability of brain structures across individuals. For example, as seen in Fig. 1 two healthy 10 year old boys can have a nearly two-fold differences in total brain size. This high variability extends to measures of brain substructures as well and has important implications for the interpretation and utility of brain imaging results. Second, the development of total cerebral volume and many subcortical regions follows an inverted U shaped trajectory. These trajectories were estimated using statistical methods which derive an overall developmental curve for a population, including an approximate age of peak volume for the population as a whole (see Fig. 2) (Lenroot et al. 2007). A third key finding is the difference in developmental trajectories for males and females. Throughout childhood and adolescence in this sample the group average brain size for males is approximately 10% larger than for females. This 10% differences has also been found in hundreds of adult neuroimaging and postmortem studies, frequently attributed to the larger
