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Context-dependent reinforcement learning impairment in depression

Backgrounds:Value-based decision-making impairment in depression is a complex phenomenon: while some studies did find evidence of blunted reward learning and reward-related signals in the brain, others indicate no effect. Here we test whether such reward sensitivity deficits are dependent on the overall value of the decision problem.Methods:We used a two-armed bandit task that includes two different contexts: one ‘rich’ context where both options were associated with an overall positive expected value and a ‘poor’ context where options were associated with overall negative expected value. We tested patients (N=30) undergoing a major depressive episode and age, gender and socio-economically matched controls (N=26). To assess whether differences in learning performance were due to a decision or a value-update process, we also analysed performance in a transfer phase, performed immediately after the learning phase. ResultsHealthy subjects showed similar learning performance in the ‘rich’ and the ‘poor’ contexts, while patients showed reduced learning in the ‘poor’ context. Analysis of the transfer phase showed that the context-dependent deficit in patients generalized when options were extrapolated from their original learning context, thus suggesting that the effect of depression has to be traced to the outcome encoding, rather than the decision phase.ConclusionsOur results illustrate that reinforcement learning deficits in depression are complex and depend on the value of the context. We show that depressive patients have a specific trouble in contexts with an overall negative state value, supporting the relevance of setting up patients in a spiral of positive reinforcement.