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Inhibition, Serotonin and Depression

Peter Dayan

Gatsby Computational Neuroscience Unit, UCL , UK

Serotonin is a neuromodulator that appears to be critically involved in a wealth of normal behaviors and also psychiatric conditions, including depression, anxiety, panic, and obsessive compulsions. However, many questions remain about its normal functional roles, and how they are compromised in disease. I will talk about the consequences of two related suggestions, that serotonin is involved in predictions of aversive outcomes, and that, associated with this predictive capacity, it is involved in behavioral inhibition to avoid those outcomes. In the context of a highly simplified model of chains of affectively-charged thought, we show how inhibition skews evaluations in favor of unwarranted optimism and how depleting serotonin might therefore lead to more normative, and more pessimistic, evaluations.