There is no agreed upon definition of ELS; indeed, there is considerable controversy about the definition of stress more generally (Levine and Ursin, 1991). Our research network adopted a working definition of ELS based on the following arguments. Stressors are events or conditions that threaten, or are perceived to threaten, physiological equilibrium (Weinstock, 2005). Stress responses involve activity in the central nervous system to mobilize endocrine, autonomic, and behavior systems to support protection from and/or adaptation to threat. Recently the concept of allostasis has been introduced to describe the dynamic interaction of multiple systems of equilibrium maintenance (McEwen, 1998, 2003). ELS or early life allostasis refers to responses to stressors experienced during pre-pubertal development. While acknowledging that ELS can involve physical stressors, we chose to focus on adverse caregiving in order to ground our work in the early experience animal data. Furthermore, we focused on stressors experienced during the first years of life when the child is nearly wholly dependent on caregivers for its survival.
