Our studies to date have demonstrated regionally specific changes in heritability. Previous studies have shown that the nonlinear characteristics of brain developmental trajectories only become prominent when longitudinal data and large samples are available (Giedd et al., 1999; Lenroot, Gogtay, et al., 2007), and that trajectories may be more informative regarding neurodevelopmental differences between groups than cross-sectional measures (Shaw et al., 2006). Longitudinal analyses will be necessary to determine whether these trajectories themselves are heritable, and our group and others have embarked on following pediatric twins over time to be able to address such questions. Another implication of the findings by ourselves and others that the brain continues to show dynamic changes over the life span is that heritability may also continue to change after early adolescence. Studies of age effects on heritability at the other end of the life span are also sparse. A longitudinal study in elderly male twins described ongoing strong genetic effects despite age-related changes in cortical features such as increased size of the lateral ventricles, supporting that age-related changes during senescence may also be genetically mediated (Pfefferbaum, Sullivan, & Carmelli, 2004).
