The sickness response

Abstract

If one thinks about how it felt the last time one came down with the flu or had a serious cold, negative emotions and bodily experiences are likely to come to mind. Feeling somewhat depressed, a bit worried or anxious, fatigued, and sore would be typical, as well as wanting to limit the number of social interactions. This chapter explains why these kinds of reactions are triggered when danger arises, especially when your body is threatened from within at the micro level, such as when bacteria or viruses are detected. These behavioral responses are collectively called sickness behavior or sickness response, and are displayed—as far as we can observe them—in very similar ways in animals and humans, to save energy and to improve survival. Even though the behavioral changes are adaptive in the short run, they are maladaptive if unabated. The chapter describes how healthy people, or even the researchers themselves, can be made purposely sick by injection of a small and non-dangerous fragment of a bacterium, resulting in a few hours of malaise during which the brain, behaviors, and the subjective health experience can be studied.