Ontogeny of stress reactivity in the human child: Phenotypic flexibility, trade-offs, and pathology

Abstract

We humans are highly sensitive to our social environments. Our brains have special abilities such as empathy and social foresight that allow us to understand each other's feelings and communicate in ways that are unique among all living organisms. Our extraordinary social minds, however, come with some significant strings attached. Our emotional states can be strongly influenced by what others say and do. Our hearts can soar, but they also can be broken. Our bodies use internal chemical messengers-hormones and neurotransmitters-to help guide responses to our social worlds. From romantic daydreams to jealous rage, from orgasm to lactation and parent-child bonding, the powerful molecules produced and released by tiny and otherwise seemingly insignificant cells and glands help orchestrate our thoughts and actions. Understanding this chemical language is important for many research questions in human health. Here we focus on the question of why social relationships can affect health-why it is that words can hurt children. Stress hormones appear to play important roles in this puzzle. The hypothalamic-pituitary-adrenal axis (HPAA) is highly responsive to traumatic experiences including social challenges. For the past 23 years we have conducted a field study of child stress and family environment in a rural community in Dominica. The primary objective is to document hormonal responses of children to everyday interactions with their parents and other care providers, concomitant with longitudinal assessment of developmental and health outcomes. Results indicate that difficult family environments and traumatic social events are associated with temporal elevations of cortisol and elevated morbidity. The long-term effects of traumatic early experiences on cortisol profiles are complex and indicate domain- specific effects, with normal recovery from physical stressors, but some heightened response to negative-affect social challenges. These results are consistent with the hypothesis that developmental programming of the HPAA and other neuroendocrine systems associated with stress responses may facilitate cognitive targeting to salient social challenges in specific environmental contexts.