Adversity across time: Do sensitive periods across the life span determine adversity-induced epigenetic changes?

Adversity exposure is linked to poor cognitive, physical, and psychiatric outcomes, yet there is great variability in outcomes following adversity. Sensitive periods are developmental periods characterized by increased susceptibility to certain types of stimuli or sensory information, which then shape future behavior and capabilities. Emerging evidence suggests that sensitive periods may play a role in the variability in health outcomes following adversity exposure via epigenetic mechanisms. Insight into the mechanisms in relation to sensitive periods could also help to determine biomarkers of risk, mechanism-informed interventions and, importantly, pinpoint the optimal times to intervene to minimize the effects of adversity. In this chapter, we highlight prominent human studies on the time-dependent effects of adversity on DNA methylation, the most studied epigenetic mechanism. The studies are grouped by developmental stage, i.e., prenatal period, childhood, adolescence, adulthood, in which the adversity exposure occurred. We feature studies using a candidate gene approach and, whenever possible, genome-wide level analyses. Lastly, we provide an overview of some of the limitations of the current literature and considerations for future inquiry within this exciting, and rapidly evolving, line of research.