From Neural Circuits to Behavior: Examining the Central Role of Anhedonia in Major Depression.

Major depressive disorder (MDD) is ranked as one of the most debilitating conditions worldwide (Malhi GS, Mann JJ. Lancet 392:2299-2312, 2018). Anhedonia, a core symptom of MDD, is described as an inability to experience pleasure and a lack of motivation. Emerging evidence highlights anhedonia's contribution to MDD trajectory, including treatment response and remission. Over the years, the conceptualization of anhedonia has evolved from a simple "loss of pleasure" to encompassing a wide range of reward-processing deficits. Shifting focus from the consummatory aspect of pleasure unveiled the multifaceted nature of anhedonia that involves other forms of reward experiences, including interest, anticipation, motivation, effort, and expectation. The aim of this chapter is to summarize current evidence in the literature of anhedonia in the context of its definitions, neurobiological features, and treatment strategies.