The influence of proximal risk on the early development of the autonomic nervous system

•We review literature on the early development of the autonomic nervous system.•We focus on the way in which proximal risk influences parasympathetic and sympathetic function.•We review examples that span from the prenatal period to very early childhood.•We focus on the effects of maternal stress, substance use, parenting, and disruptions to parenting.

In this paper we review the evidence linking the early development of the autonomic nervous system in early childhood to four proximal risk factors: maternal stress during pregnancy, maternal substance use during pregnancy, poor-quality parent–child interactions, and specific disruptions in parenting behavior. A clear pattern of altered autonomic function emerges in children exposed to proximal risk, marked by reduced parasympathetic tone under conditions of both homeostasis and challenge, accompanied by increased sympathetic tone in some cases. This pattern of autonomic activity would support increased vigilance and active defense responses, which, in an environment of high proximal risk, may be adaptive in the short-term. However, in the long-term maintaining such a state may impose a high allostatic load. The current paper reviews and interprets the current literature and discusses future directions.