A theme of our ADHD studies is that clinical improvement is often mirrored by a convergence of developmental trajectories toward typical development and that persistence of ADHD is accompanied by a progressive divergence away from typical development. We have demonstrated this for the cortex, where right parietal cortical normalization accompanied clinical improvement (Shaw et al., 2006b)—and for the cerebellum, where progressive volume loss of the inferior posterior lobes mirrors persistence of ADHD (Mackie et al., 2007). A similar principle may hold for the hippocampus: children with ADHD who remit show a trajectory that is similar to that of typical development, whereas persistent ADHD is accompanied by a progressive loss of hippocampal volume (Shaw et al., 2007b). These highly significant findings occur independently, and thus one cannot simply see ADHD as “delayed frontal development.” It also should be stressed that, to date, these measures alone or combined are not clinically useful for either diagnosis or clinical outcome.
