Environmental and neurodevelopmental contributors to youth mental illness

Abstract

While a myriad of factors likely contribute to the development of mental illness in young people, the social environment (including early adverse experiences) in concert with neurodevelopmental alterations is undeniably important. A number of influential theories make predictions about how and why neurodevelopmental alterations may mediate or moderate the effects of the social environment on the emergence of mental illness. Here, we discuss current evidence supporting each of these theories. Although this area of research is rapidly growing, the body of evidence is still relatively limited. However, there exist some consistent findings, including increased striatal reactivity during positive affective processing and larger hippocampal volumes being associated with increased vulnerability or susceptibility to the effects of social environments on internalizing symptoms. Limited longitudinal work has investigated neurodevelopmental mechanisms linking the social environment with mental health. Drawing from human research and insights from animal studies, we propose an integrated mediation-moderation model and outline future research directions to advance the field.

Fig. 1. Integrated mediation-moderation model of the role of neurodevelopment in linking the social environment with mental health.

+’ve = positive environmental exposure, −’ve = negative or adverse environmental exposure. a During early life, both positive and adverse environments lead to accelerated hippocampal maturation, resulting in a nonlinear association between the social environment and hippocampal volume. b Adverse early environments lead to early maturation, followed by a stunting of hippocampal growth during childhood and adolescence, increasing risk for mental health problems. c Larger hippocampal volumes following early accelerated hippocampal maturation engender increased sensitivity to later positive and adverse environments.