The human brain can be conceptualized as a complex, hierarchical network, in which billions of neurons are precisely organized into circuits, columns, and functional areas. Information processing arises from specific patterns of spatio-temporal activity over these neurons, intimately linking brain structure and function. The physical structure of brain networks necessarily constrains network dynamics (consider the effects of synaptic pruning, myelination, or lesions (He et al., 2007; Huttenlocher, 2002; Sur and Rubenstein, 2005)), and network dynamics can reshape the physical structure of the network (e.g., through Hebbian plasticity (Katz and Shatz, 1996; Majewska and Sur, 2006)). Thus, this network has a structural/functional trajectory from conception through development into adulthood, and possibly into senescence, which is governed by programmed biological events and the experiential history of the person. Describing this network and its trajectory across the human lifespan should be a fundamental goal of neuroscience, the importance of which was recently underscored by the establishment of the NIH Human Connectome Project (N.I.H.; Sporns et al., 2005).
