Author:

Abstract:

Fear and anxiety serve adaptive functions. However, they become maladaptive when they are not fading away when the threat is over (impaired extinction), when they induce avoidance behaviors interfering with daily functioning (excessive avoidance), or when they spread to harmless situations (overgeneralization). While anxious individuals often show impaired fear extinction, excessive fear avoidance, and fear overgeneralization, these behavioral profiles are not always observed. Also, despite the high comorbidity rate with anxiety, how depression might affect the transition from adaptive to maladaptive anxiety remains surprisingly understudied. Depressed individuals often have negative expectations, feel a lack of control, cannot enjoy positive events, and hold onto negative expectations even when positive events do occur. These features may lead to impaired fear extinction and fear overgeneralization similar to those seen in anxiety. However, due to anhedonia, they may exhibit insufficient avoidance. This dissertation hypothesizes that controlling aversive events is inherently rewarding, but less so for people with anhedonia. As a result, they are less motivated to engage in behaviors aimed at controlling aversive events, resembling a learned helplessness state. Therefore, studying the role of anhedonia in active avoidance learning provides a potential pathway from anhedonia to learned helplessness and helps to understand the mechanism of active avoidance learning. The first aim of this dissertation (Chapter 2) was to examine not only the anxiety- but also depression-related individual differences in extinction, avoidance, and generalization of fear. Chapter 3 & 4 present two experimental studies investigating if anhedonia indeed impairs the pleasure of controlling aversive events and therefore reduces threat avoidance behaviors. Using different types of threats and various measures of anhedonia, both studies confirmed our hypothesis. Our hypothesis that anhedonia attenuates relief, a pleasant feeling triggered by successfully controlling aversive event, is based on the assumption that relief is rewarding in nature. However, this lacks direct empirical support so far. Chapter 5 & 6 report two studies that found the relief experience after successful threat avoidance to be comparable to receiving monetary rewards across the subjective, behavioral, psychophysiological, and neural levels. Finally, Chapter 7 discusses the anhedonia effects, the rewarding nature of relief observed in this dissertation, and their contribution to understanding avoidance learning mechanisms. Limitations of the current studies are also addressed and suggestions for future research into anhedonia and relief are provided.