Common psychiatric treatments alter affective dynamics

Affective states are dynamic, fluctuating in response to recent events: an unexpected pleasure, a disappointing loss. Affective biases, which cause disruptions in these dynamics, are core components of mental ill-health, but the specific effects of treatments on these biases are poorly understood. Here, we investigate the impact of common psychiatric treatments on subjective assessments of happiness, confidence, and engagement during a reinforcement learning task (N=935; 130 taking antidepressant medications). Half (N=459) of the participants were randomised to practice a common psychotherapeutic technique—cognitive distancing—throughout the task. From a joint computational model of learning and affect, we find evidence for distinct and overlapping impacts of psychiatric treatments on affective dynamics. Cognitive distancing attenuates downward drift in happiness and engagement and increases recency bias in the affective impact of recent choices. Conversely, antidepressant use increases baseline happiness and confidence in individuals with similar levels of current symptoms, and decreases recency bias such that more past events influence affective states. Crucially, both cognitive distancing and antidepressant use converge to dampen negative biases in happiness and confidence specifically in participants experiencing higher levels of anxiety and depression symptoms. Together, our results indicate that common treatments for mental ill-health may alter symptoms through their impact on affective dynamics, but via distinct mechanisms.