Maturational themes relevant to both health and illness include the importance of considering developmental trajectories and the high variability of measures across individuals. Despite high individual variation, several statistically robust patterns of average maturational changes are evident. Specifically, WM volumes increase and GM volumes follow an inverted U developmental trajectory with peaks latest in high association areas such as dorsolateral prefrontal cortex. These anatomic changes are consistent with electroencephalographic, functional MRI, postmortem, and neuropsychological studies indicating an increasing “connectivity” in the developing brain. “Connectivity” characterizes several neuroscience concepts. In anatomic studies, connectivity can mean a physical link between areas of the brain that share common developmental trajectories. In studies of brain function, connectivity describes the relationship between different parts of the brain that activate together during a task. In genetic studies, it refers to different regions that are influenced by the same genetic or environmental factors. All of these types of connectivity increase during adolescence. Characterizing developing neural circuitry and the changing relationships among disparate brain components is one of the most active areas of neuroimaging research as detailed by Power et al. (2010)
(this issue of Neuron
Although other higher association areas also mature relatively late, the developmental course of the dorsolateral prefrontal cortex has most prominently entered discourse affecting the social, legislative, judicial, parenting, and educational realms because of its involvement in judgment, decision making, and impulse control. It is also consistent with a growing body of literature indicating a changing balance between earlier-maturing limbic system networks (which are the seat of emotion, and later-maturing frontal lobe networks) and later-maturing frontal systems (Casey et al., 2010a
[this issue of Neuron
]). The frontal/limbic relationship is highly dynamic. Appreciating the interplay between limbic and cognitive systems is imperative for understanding decision making during adolescence.
Psychological tests are usually conducted under conditions of “cold cognition”—hypothetical, low-emotion situations. However, real-world decision making often occurs under conditions of “hot cognition”—high arousal, with peer pressure and real consequences. Neuroimaging investigations continue to discern the different biological circuitry involved in hot and cold cognition and are beginning to map how the parts of the brain involved in decision making mature. For instance, adolescents show exaggerated nucleus accumbens activation to reward compared to children but not a difference in orbital frontal activation (Galvan et al., 2006
). Prolonged maturation of the PFC has also been shown to be related to age-related improvement in memory for details of experiences (in contrast to earlier maturing medial temporal lobe structures subserving nonexperiential memories) (Ofen et al., 2007
The “journey as well as the destination” tenet highlights the fundamentally dynamic nature of brain and cognitive development in children. Adolescence is a particularly critical stage of neural development, and the relationship between typical maturational changes and the onset of psychopathology in this age group is an area of active investigation. The onset of several classes of psychiatric illness in the teen years (e.g., anxiety and mood disorders, psychosis, eating disorders, and substance abuse) (Kessler et al., 2005
) may be related to the many brain changes occurring during this time (Paus et al., 2008
). More broadly, understanding the mechanisms and influences on structural and functional brain development across childhood may help us to harness the brain’s developmental plasticity to help guide interventions for clinical disorders and for elucidating the path to promote optimal healthy development.