These three changes – the change in the ratio of grey to white matter in prefrontal areas, the increase in connectivity between prefrontal and other regions, and the increase in dopaminergic activity in prefrontal-striatal-limbic pathways – provide the basis for a theory that links brain maturation in adolescence to increased vulnerability to risky behavior. The basic framework, articulated in slightly different versions by many writers, including Casey (Casey et al., 2008), Dahl (2004), Ernst (Ernst et al., 2006), Spear (2009), and myself (Steinberg, in press), posits that middle adolescence is a time of heightened vulnerability to risky and reckless behavior because of the temporal disjunction between the rapid rise in dopaminergic activity around the time of puberty, which leads to an increase in reward-seeking, and the slower and more gradual maturation of the prefrontal cortex and its connections to other brain regions, which leads to improvements in cognitive control and in the coordination of affect and cognition. As dopaminergic activity declines from its early adolescent peak, and as self-regulatory systems become increasingly mature, risk-taking begins to decline.
