Studies focusing on key developmental milestones show that puberty is a sensitive period associated with the onset and/or increase of emotional and behavioural problems, including substance-use. Early-maturing adolescents have been shown to initiate smoking and drinking earlier and to be more likely to experiment with other illegal substances than later-maturing adolescents.
Studies investigating key cognitive and neural changes occurring during this maturational period have contributed to the formulation of a “dual-systems” model of risk for addiction (Steinberg, 2008
), which posits that heightened risky behaviours in adolescence, including substance-use, are a product of the interaction between the level of development of two distinct neurobiological systems: a socio-emotional system, localized primarily in limbic and paralimbic areas of the brain, and a cognitive-control system, mainly associated with lateral prefrontal and parietal cortices. According to this model, risky behaviours increase due to a relatively more rapid development of the socio-emotional system, which is hypothesized to lead to increases in doparminergic activity and sensation-seeking. However, this happens before the cognitive control system, associated with self-regulation and impulse control, is fully developed, which is not until the end of adolescence or early adulthood. Vulnerability to risk-taking during adolescence would therefore be heightened when a fast-developing socio-emotional system combines with a slow-developing cognitive control system.
It is well established that, regardless of developmental period, chronic exposure to alcohol and drugs is associated with neural changes in the reward circuitry of the brain (Robison & Nestler, 2011
), However, developmental studies suggest that as the adolescent brain undergoes significant neuromaturation it is particularly susceptible to damage caused by acute and chronic effects of alcohol. This has been shown to be true in rodent models (Crews, He, & Hodge, 2007
) and humans (McQueeny et al., 2009
), where alcohol-neurodegeneration is more severe in adolescent than adult brains, particularly in the hippocampus and areas of the prefrontal cortex. In addition to this neurodegeneration, alcohol-related neuropsychological deficits have also been shown in adolescents, even in non-problematic, social drinking adolescents (Squeglia, Spadoni, Infante, Myers, & Tapert, 2009
). This is compounded by the fact that animal studies show that adolescents are not only more sensitive to the cognition-impairing effects of alcohol, but that they are less sensitive than adults to the motor-impairing and sedative effects of alcohol. The reduced sensitivity to these aversive effects, typically associated with moderate alcohol consumption, may contribute to the high rates of binge drinking in adolescence. These and human neuroimaging studies have inspired a new area of research in the field of addiction treatment which attempts to enhance neurocognitive factors that may be impaired in adolescent and adult substance users (Houben, Wiers, & Jansen, 2011
Studies focusing on social development have shown that in addition to the physical and biological changes described above, children’s social environments also change dramatically during adolescence. Not only are there changes in school environment brought about with the entry to high-school, where peer groups widen, and supervision becomes more diffused among multiple teachers, but other important changes happen within the family and peer groups. As children move into adolescence, they spend less time with the family, favoring time and activities with peers where quality adult supervision is reduced. This does not mean, however, that family factors do not play an important role in children’s development during this period. A positive relation with one’s parents (i.e., feeling accepted, good communication, parental monitoring) has been shown to reduce future alcohol consumption (Nash, McQueen, & Bray, 2005
). Conversely, parents of children who later go on to develop substance abuse problems tend to decrease family management in early- to mid-adolescence.
Although a number of positive outcomes have been identified as coming from greater autonomy and affiliation with peers, affiliation with deviant or substance-using peers is associated with a higher risk of engaging in substance-use, delinquency and risk-taking behaviours (Gardner & Steinberg 2005
). Youth’s perception of social norms around substance-use has been shown to impact on their behaviours, and many youth overestimate levels of substance-use among peers, and are consequently more likely to use substance themselves (Edwards et al., 2008
). A number of studies have demonstrated that the effect of peers on risk-taking behaviours is at its strongest in early- to mid-adolescence, and that peer acceptance activates the same brain regions as other non-social-based rewards (Guyer, Chaote, Pine, & Nelson, 2012
), and may therefore facilitate substance-use in peer contexts.