Computationally Informed Insights Into Anhedonia and Treatment by Kappa Opioid Receptor Antagonism.

BACKGROUND

Anhedonia, the loss of pleasure, is prevalent and impairing. Parsing its computational basis promises to explain its transdiagnostic character. One manifestation of anhedonia, reward insensitivity, may be linked to limited memory. Furthermore, the need to economize on limited memory engenders a perseverative bias toward frequently chosen actions. Anhedonia may also be linked with deviations from optimal perseveration for a given memory capacity, a pattern that causes inefficiency because it results in less reward for the same memory cost.

METHODS

To test these hypotheses, we applied a theory of optimal decision making under memory constraints that decomposes behavior into a memory component and an efficiency component. We applied this theory to behavior on the Probabilistic Reward Task, a reward learning paradigm that has been validated in anhedonia, and performed secondary analysis of a randomized controlled trial testing kappa opioid receptor (KOR) antagonism for anhedonia (n = 24 KOR; n = 31 placebo), as well as analyses of 3 other datasets (n = 100, 66, 24, respectively). We fit a resource-bounded reinforcement learning model to behavior.

RESULTS

Across clinical and nonclinical populations, anhedonia was associated with deficits in efficiency but not memory. The reinforcement learning models demonstrated that deficits in efficiency arise from the inability to perseverate optimally. KOR antagonism, which likely elevates tonic dopamine, increases both memory and efficiency, and the model demonstrated that this arises from increased reward sensitivity and perseveration.

CONCLUSIONS

Therefore, KOR antagonism has distinct cognitive effects, only one related to anhedonia. These findings have potential implications for the applications of KOR antagonists.