Exploring individual differences in anhedonia using psychometric, behavioural and electrophysiological methods.

Abstract

Depression affects over 300 million people and is a leading burden of illness worldwide. Despite its prevalence, highly effective treatments for depression are lacking. The absence of efficacious treatment may be due to poor understanding of the symptoms underpinning depression. One important indicator of poor response to treatment is the symptom, anhedonia. Anhedonia presents as impaired reward processing, particularly approach motivation, and is a transdiagnostic symptom common to depression, schizophrenia, Parkinson’s Disease and addiction. Individual differences in anhedonia reveal a trait-like stability for this construct, suggesting clinical utility as a marker of treatment response and psychopathology. However, the putative utility of anhedonia is undermined by inconsistencies and inaccuracies in the measurement of this construct. This thesis aimed to investigate the measurement of motivational processes in anhedonia and sought to develop a new self-report measure, sensitive to the multifaceted nature of individual differences in anhedonia. Two initial studies sought to examine the convergent validity of neural (EEG cerebral asymmetry), behavioural and psychometric measures of approach and withdrawal motivation. These studies suggested that, contrary to much of the literature, these measures are assessing discrete sub-components of approach and withdrawal motivation. Two subsequent studies sought to develop and validate a self-report measure of multidimensional anhedonia. The Goldsmiths Anhedonia Measure (GAME) yields a four-factor structure, sensitive to individual differences in interpersonal, emotional, sensory and novelty-seeking aspects of reward processing. Finally, the putative causal relationship between perceived stress and anhedonia was examined. Reflecting the multi-dimensional nature of anhedonia suggested by prior studies, perceived stress predicted anhedonia only in interpersonal, emotional and anticipatory domains (but not sensory, novelty-seeking or consummatory areas). These findings highlight the need to refine measurement of motivational processes in anhedonia to better characterise individual differences in treatment response and contribute to the theoretical understanding of a multifaceted reward “wanting” process.