Imaging techniques, in particular MRI and fMRI have allowed for large quantitative cross sectional and longitudinal studies of the trajectory of brain development over adolescence to be mapped (see [69-70] for review). These studies have added temporal detail to the histochemical studies and have demonstrated that cortical volume decreases across adolescence while white matter volume increases, particularly in the prefrontal cortex [71]. A different approach has been accomplished by studies utilizing Graph Theory analyses to evaluate patterns of low frequency temporal correlations in fMRI signal to determine how network characteristics of brain-wide patterns may change from childhood to adulthood. These studies suggest that in childhood brain networks are more localized with the functional connectivity being more short range, whereas in adults the networks are spread out over larger areas with more long-range connections [72-75]. While these structural studies provide important information on the trajectory of brain development they shed less light on how changes in cognitive functions are related to brain activity in specific neuronal networks, in real time, and how those functions might change over the lifespan [76].
