The aim of this project was to review and analyze the available studies on the bidirectional nature of sleep (sleep duration, sleep quality, sleep/wake problems, insomnia) and externalizing behavior (aggression, hyperactivity, delinquency, impulsivity, attentional problems). We aim to provide initial answers to the following research questions: Does externalizing behavior cause sleep problems? Do sleep problems cause externalizing behavior? Or is the relationship reciprocal, with sleep problems predisposing to externalizing behavior which then feeds into further sleep problems? Alternatively, is any bidirectional relationship confounded by other factors? Furthermore, do different sleep measures (objective vs subjective vs a combination of both) influence study outcomes? What are potential mechanisms governing this association? Finally, what are the limitations of existing studies, and how may these gaps be addressed in future research? 

Gaining more insights into reciprocal links between sleep and externalizing behavior is of potential importance to clinical practice in that both sleep and behavioral symptoms, rather than one but not the other, may be targeted in therapy to effectively tackle a self-perpetuating deleterious sleep-mental health cycle. We posit that this finding might be particularly beneficial for subclinical populations struggling with sleep and/or behavioral problems: breaking their cycle with such a two-pronged therapeutic approach at early stages of the impairment can prevent more severe clinical health problems from emerging.