Emotion—cortisol Transactions Occur over Multiple Time Scales in Development: Implications for Research on Emotion and the Development of Emotional Disorders

In understanding the associations between emotional experience and physiological processes, time is a central variable.Most physiological processes are moving targets—they change from moment to moment and over the course of days, months, and years. Stress-sensitive physiological systems, such as the hypothalamic-pituitary-adrenal (HPA) axis and the sympathetic nervous system, are in fact designed to change over time in relation to changing internal and external conditions. This notion of adaptive flexibility in physiological functioning has been termed “allostasis,” in contrast to models emphasizing the importance of physiological stability or “homeostasis” (McEwen, 1998; Sterling, 2003). Adaptive changes in physiology occur both in response to, and in anticipation of, experience, with the goal of helping the body prepare for, cope with, and recover from social, emotional, and physical challenges (McEwen, 1998; Sterling, 2003). In this chapter, I focus on the HPA axis as an allostatic system and introduce a chronometric model (see Figure 2) suggesting that HPA-axis changes (as indexed by changing salivary cortisol levels) occur in response to social and emotional experience over multiple time courses in development. I provide examples of research on children and adolescents showing the relevance of various time courses of cortisol change (ranging from moment-to-moment changes to changes occurring over the course of days, months, and years) for understanding individual differences in state and trait emotion and the development of emotional disorders. Using illustrations from my own research on adolescents at risk for the development of major depressive disorder (MDD), I show how a consideration of multiple time scales of cortisol change, combined with careful design, measurement, and use of multilevel analyses, can