Model-based planning is unaffected by ketamine, antidepressant and internet delivered cognitive behavioural therapy treatments in depression.

Cognitive impairments have been observed in patients with depression. These include deficits in inhibition, shifting, and updating; cognitive processes that are critical for goal-directed control over behavior ('model-based planning'). Nevertheless, results of model-based planning in depression have been mixed. We aimed to address this by taking a within-person approach, examining model-based planning before and after a range of effective treatments for depression. Across two parallel studies, participants completed a two-step reinforcement learning paradigm before and after antidepressant medication, internet-based cognitive behavioral therapy (iCBT) or intravenous (IV) ketamine infusion. In experiment 1, 93 patients with treatment-resistant depression were randomized to a single dose of IV ketamine (0.5 mg/kg) or IV saline (50 mL 0.9% NaCl). In Experiment 2, 781 participants were followed for four weeks of antidepressant (N = 83), or iCBT (N = 611) treatment. N = 87 participants without any psychiatric diagnosis were followed as a control group. In both experiments, depressive symptoms significantly improved in treatment groups compared to their corresponding control groups, but we did not find evidence of changes in model-based planning. Moreover, we failed to find associations between individual differences in model-based planning and differential response to ketamine, iCBT or antidepressant treatments. Individual differences in model-based planning at baseline were associated with compulsivity, but not with depression symptoms. These findings suggest that model-based planning is not necessarily compromised in depression and does not improve following treatments. This result provides evidence for the trait-like nature of model-based planning and underscores the specificity of its relation to disorders of compulsivity.