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).
