Anhedonia and depression in youth: real-world and computational evidence of impaired reward processingSahni, A. (2025) Anhedonia and depression in youth: real-world and computational evidence of impaired reward processing. PhD thesis, University of Reading
It is advisable to refer to the publisher's version if you intend to cite from this work. See Guidance on citing. To link to this item DOI: 10.48683/1926.00124059 Abstract/SummaryBackground: Major Depressive Disorder (MDD) is the leading cause of disability in young people, and predicts increased risk of suicide and unemployment in adulthood. Anhedonia, the loss of interest and pleasure, is a core symptom of depression. Impairments in reward processing sub-components (anticipation, motivation, consummatory and learning) are thought to underlie anhedonia symptoms. Discovering novel reward-based treatment targets in young people could protect against poor outcomes in adulthood. Ecological momentary assessment (EMA) questionnaires examine reward processing in real-life, removing recall biases. Previous EMA studies have demonstrated deficits in anticipatory and consummatory pleasure in depression vs controls. Studies have also reported lower mood in depressed individuals, i.e. lower positive affect (PA) and elevated negative affect (NA). The Mood brightening (MB) effect has been observed, where positively-rated events lead to greater increases in PA and greater reductions in NA in depression vs controls. Lab-based experimental tasks demonstrate depressed individuals less frequently choose to exert effort for rewards, suggesting deficits in motivation. Probabilistic learning tasks show individuals failing to develop response biases to more rewarding choices, suggesting reduced exposure to rewarding experiences in depression. Leisure activities and social company are known to protect against depression, but inactivity and social isolation are more prevalent. Understanding how to increase compliance with rewarding activities would improve outcomes in depressed youth. However, how to increase enjoyment and engagement in pleasurable activities remains unclear, and the MB effect of such activities remains scarcely examined. Lastly, experimental tasks have rarely combined learning to maximize rewards with exerting effort to attain them, which closely capture the real-life dynamics of reward processing. Methods: Young people (16-25 yrs old) were recruited from local schools and the university. Depression symptoms were measured using the Mood and Feelings Questionnaire (MFQ) and the Beck Depression Inventory-II (BDI). Anhedonia symptoms were measured using the Temporal Experience of Pleasure Scale (TEPS), the Snaith-Hamilton Pleasure Scale (SHAPS), and the Anhedonia Scale for Adolescents (ASA). The EMA protocol adapted from Edwards et al. (2018), presenting seven daily assessments for 6 days on smartphones. Participants selected from multiple choices for physical activities and company, then rated anticipation (anticipatory pleasure, expectation) and motivation (preference, interest) for planned activities, enjoyment of current activity, and mood (PA, NA) on 7-point Likert scales. The physical activities were categorised as Leisure (relaxing, exercising, other leisure activities) or Functional (work/school, hygiene, etc.), and company as Social (friends, family, partner) or Non-Social (alone). In Paper 1, participants (N=80; 2,316 assessments) were classified by depression severity: high (HD, MFQ ≥ 27, n=42), moderate (MD, MFQ 16–27, n=16), and controls (C, MFQ ≤ 16, n=22). Multilevel models examined time-lagged relationships: how anticipation and motivation (t-1) predict the enjoyment and engagement in Leisure activities and Social company (t). Linear regressions examined how depression symptoms predict time spent in activities. Paper 2 used EMA mood data from participants (N=71; 2,177 assessments). Affective reactivity was measured as change from two baselines: mean affect and affect (t-1). Multilevel models examined how depression and anhedonia symptoms (MFQ, ASA) predicted reactivity, and how context (Leisure, Social) moderated this relationship. For Paper 3, an online reward and effort learning task was adapted from Frey et al. (2023). Participants (N=155) chose between two shapes, each requiring effort exertion (high/low button presses) to acquire rewards (puppy/dog image). Reward and effort learning blocks, 25 trials each, required participants to maximize reward or minimize effort, respectively. Outcome contingencies were 25/75%. Q-learning equations modelled choice data with parameters (learning rate, explore/exploit parameter) capturing aspects of learning. Correlations examined relationships of anhedonia (SHAPS, TEPS) with subjective ratings of rewards (liking, wanting, effort willingness), task performance, and parameter values. Corrected for multiple comparisons. Results: Paper 1 revealed young people with higher depression symptoms spent less time on work/school and hygiene. When planned (t-1) and actual activities (t) matched, higher anticipatory pleasure predicted greater engagement and more enjoyment from leisure activities and social company in HD group (Paper 1). Paper 2 revealed that engaging in leisure activities or social company predicted greater decreases in NA at higher depression symptoms, but not PA. As expected, Paper 3 revealed lower liking, wanting and effort willingness for puppy images with increasing anhedonia. Further, lower effort and reward learning accuracies correlated with increasing consummatory anhedonia. Computational modelling revealed that higher temperature values may underlie this, suggesting over-exploration of less rewarding options. Limitations: As the sample consisted mostly of highly-educated females, generalizability of these findings is limited. Seven questionnaires per day restrict the number of time-lagged relationships that can be captured. Preference for puppy and dog images may vary, which may influence results. Conclusions: Episodic future thinking (EFT) is shown to enhance anticipatory pleasure. Future studies should examine if EFT increases enjoyment and engagement in leisure activities and social company in depression. These activities are likely to elevate mood by reducing NA at higher depression symptoms, so managing negative emotions could be encouraged in depressed individuals. Exploring how social rewards are processed using the reward and effort learning task and EMA is encouraged, as these are more salient for young people. Studies are novel - a strength but few previous studies to evaluate findings against. Replication of all studies in larger samples is suggested.
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