A prominent tenet now established in the neuroimaging literature is that the shape of the age by size trajectories may be related to functional characteristics even more so than the absolute size. For instance, in a longitudinal study comprising 692 scans from 307 typically developing subjects, age by cortical thickness developmental curves were more predictive of IQ than differences in cortical thickness at age 20 years (Shaw et al., 2006a). Age by size trajectories are also more discriminating than static measures for sexual dimorphism where lobar peak GM volumes occur 1–3 years earlier in females (Lenroot et al., 2007). Trajectories are increasingly being employed as a discerning phenotype in studies of psychopathology as well (Giedd et al., 2008).
