Neural systems underlying motivated behavior in adolescence: implications for preventive medicine

Abstract

Objective: Although a time of increased independence and autonomy, adolescence is also a time of vulnerabilities, through increased risk-taking and the emergence of psychopathology. Neurodevelopmental changes during this period may provide a neurobiological basis for this normative rise in deleterious behaviors. Thus, the objective of this review was to identify neurodevelopmental processes underlying the emergence of risk-taking and psychopathology in adolescence, and discuss implications of these findings for prevention.

Method: This article reviews literature examining developmental and contextual factors influencing neural functioning in systems mediating threat, reward, and cognitive control. This literature is discussed from the perspective of the Triadic Neural Systems Model of motivated behavior.

Results: Neuroimaging research suggests that neurodevelopmental and contextual factors both contribute to a shift in the functional equilibrium among the Triadic nodes. This equilibrium shift may contribute to negative outcomes of adolescent risk behavior. Most importantly, the balance of this equilibrium and its sensitivity to social and appetitive contexts may be exploited to facilitate prevention of deleterious outcomes.

Conclusion: Understanding developmental and contextual factors that influence functioning in motivational neural circuits can inform research on adolescent risk-taking, and may provide targets for novel preventions, for example through the use of incentives to reduce deleterious outcomes.

Figure 1

The Triadic Neural Systems Model of motivated behavior emphasizes the contributions of three neural systems in the unique cognitive and affective architecture of adolescent development; namely, a threat system, a reward system, and a cognitive control system. Within the Triadic Model, the striatum represents the reward system, and is associated with approach; the amygdala represents the threat system, and plays a significant role in avoiding aversive (e.g., fearful) stimuli; and the prefrontal cortex is the center of the cognitive control system, which serves to regulate threat and reward functions. Of the developmental changes typically observed in adolescence, hyperactivity in the striatum is chiefly responsible for increased risk-seeking, while hyperactivity in the amygdala is implicated in affective lability. Social reorientation involves interactions among all three systems.

Figure 2

In the context of threat (e.g., fearful social cues), adolescents display enhanced recruitment of the threat system (localized in the amygdala) and reduced recruitment of the cognitive control system (localized in the prefrontal cortex) relative to adults. This shift in the functional equilibrium among the triadic nodes may contribute to the emergence of affective intensity and lability during this developmental period.

Figure 3

In the context of reward, adolescents display preferential recruitment of the reward system over the cognitive control system when processing appetitive stimuli. This shift in the functional equilibrium among the triadic nodes may drive typical increases in risk-taking that are commonly seen among adolescents.

Figure 4

When adolescents are provided with incentives to engage cognitive control functions, such as inhibitory control and sustained attention, the deficient recruitment of the cognitive control system is ameliorated, and adolescents show marked improvements in the ability to sustain attention and inhibit prepotent responding. Thus, adolescents appear to be uniquely sensitive to the effects of incentives on cognitive control functions.