Impaired goal-directed planning in transdiagnostic compulsivity is explained by uncertainty about learned task structure

Diminished use of goal-directed (“model-based”) decision-making is a hallmark of transdiagnostic compulsivity, promoting an over-reliance on inflexible and habitual behaviours. However, the origin of this impairment remains unclear. Here, we test the hypothesis that these impairments arise due to uncertainty within the internal world model that subserves goal-directed decision-making. We adapted a validated gamified decision-making task to characterise how individuals build an internal model of an environment, pairing this data with computational modelling to uncover the exact mechanisms underpinning behaviour and quantify individual differences. Two samples of participants (a discovery and pre-registered replication sample) performed the task, and we also acquired longitudinal data over 2 week and 3 month periods to assess task reliability and stability of behaviour over time. Across discovery (n=551) and replication (n=1322) samples, we found that individuals higher in compulsivity and intrusive thought learned more slowly and formed a less certain representation of the task’s structure. This uncertainty mediated the link between compulsive symptoms and use of goal-directed behaviour. Behaviour in the task was relatively stable over a 3 month (n=385) and 1 year (n=326) period and did not predict changes in symptoms. Our results suggest that reliance on habitual behaviours seen in those with high levels of compulsive symptoms result from a tendency to form less certain internal models of the external world. Given the stability of this behaviour and its links to symptoms, this may represent a trait-level vulnerability for this symptom dimension.