Arbitration between model-free and model-based control is not affected by transient changes in tonic serotonin levels

Sage Publications 2024-02-01

Background: Serotonin has been suggested to modulate decision-making by influencing the arbitration between model-based and model-free control. Disruptions in these control mechanisms are involved in mental disorders such as drug dependence or obsessive-compulsive disorder. While previous reports indicate that lower brain serotonin levels reduce model-based control, it remains unknown whether increases in serotonergic availability might thus increase model-based control. Moreover, the mediating neural mechanisms have not been studied yet. Aim: The first aim of this study was to investigate whether increased/decreased tonic serotonin levels affect the arbitration between model-free and model-based control. Second, we aimed to identify the underlying neural processes. Methods: We employed a sequential two-stage Markov decision-task and measured brain responses during functional magnetic resonance imaging in 98 participants in a randomized, double-blind cross-over within-subject design. To investigate the influence of serotonin on the balance between model-free and model-based control, we used a tryptophan intervention with three intervention levels (loading, balanced, depletion). We hypothesized that model-based behaviour would increase with higher serotonin levels. Results: We found evidence that neither model-free nor model-based control were affected by changes in tonic serotonin levels. Furthermore, our tryptophan intervention did not elicit relevant changes in Blood-Oxygenation-Level Dependent activity.

Department of Economics; 330 Economics; Pharmacology (medical), psychiatry and mental health, pharmacology, tryptophan loading, tryptophan depletion, habitual system, goal-directed system, two-stage Markov decision task; Journal Article; PeerReviewed; info:eu-repo/semantics/article; info:eu-repo/semantics/publishedVersion

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info:doi/10.5167/uzh-254730
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https://www.zora.uzh.ch/id/eprint/254730/1/2312_Gilger_etal_JPsychopharmacology.pdf
info:doi/10.5167/uzh-254730
info:doi/10.1177/02698811231216325
urn:issn:0269-8811
1443057356

HAUPTBIBLIOTHEK UNIV OF ZURICH
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