The Hypothalamic–pituitary–adrenocortical System and Emotion: Current Wisdom and Future Directions

Measures of the hypothalamic–pituitary–adrenocortical (HPA) axis can help us understand emotional development. However, to use these measures effectively, we must remember that the HPA system evolved to serve multiple essential functions, including regulation of glucose and carbohydrate metabolism and modulation of the immune and cardiovascular systems (Sapolsky, Romero, & Munck, 2000; Schulkin, 1999). While emotions do influence the HPA axis, this system is also capable of responding when the individual is comatose. Emotions are, thus, neither necessary nor often sufficient to account for increases and decreases in HPA activity. Nonetheless, when approached with an understanding of the complexity of its regulation, HPA activity can provide insights into emotions and their role in neurobehavioral development. This chapter provides an overview of some of the critical issues and current advances in using measures of HPA activity, particularly cortisol, in developmental studies of emotion. Because the HPA axis forms one arm of the mammalian stress system, this chapter should be read in conjunction with the chapter by Obradović and Boyce in this volume, which includes discussion of the other major arm, the sympathetic-adrenomedullary system. The basic anatomy and physiology of the HPA axis and of the extrahypothalamic corticotrophin-releasing hormone (CRH) system are covered in detail in other reviews (Gunnar & Quevedo, 2007; Joëls & Baram, 2009; Korosi & Baram, 2008; Papadimitriou & Priftis, 2009; Ulrich-Lai & Herman, 2009) and will not be covered here. The remainder of the chapter is written as if the reader has a full grasp of this information. Indeed, we argue that without grounding in the biology of these systems, researchers will be unable to make much headway in using activity of the HPA axis to illuminate understanding of emotional development.