Citation

Eikemo M, Biele G, Willoch F, Thomsen L, Leknes S. Neuropsychopharmacology 2017; 42(9): 1833-1840.

Affiliation

The Intervention Centre, Oslo University Hospital, Norway.

Copyright

(Copyright © 2017, Nature Publishing Group)

DOI

10.1038/npp.2017.58

PMID

28294136

Abstract

Modifying behavior to maximize reward is integral to adaptive decision making. In rodents, the μ-opioid receptor (MOR) system encodes motivation and preference for high-value rewards. Yet it remains unclear whether and how human MORs contribute to value-based decision making. We reasoned that if the human MOR system modulates value-based choice, this would be reflected by opposite effects of agonist and antagonist drugs. In a double-blind pharmacological cross-over study, 30 healthy men received morphine (10 mg), placebo and the opioid antagonist naltrexone (50 mg). They completed a two-alternative decision making task known to induce a considerable bias towards the most frequently rewarded response option. To quantify MOR involvement in this bias, we fitted accuracy and reaction time data with the Drift Diffusion Model (DDM) of decision making. The DDM analysis revealed the expected bidirectional drug effects for two decision subprocesses. MOR stimulation with morphine increased the preference for the stimulus with high-reward probability (shift in starting point). Compared to placebo, morphine also increased, and naltrexone reduced, the efficiency of evidence accumulation. Since neither drug affected motor-coordination, speed-accuracy trade-off or subjective state (indeed participants were still blinded after the third session), we interpret the MOR effects on evidence accumulation efficiency as a consequence of changes in effort exerted in the task. Together, these findings support a role for the human MOR system in value-based choice by tuning decision making towards high-value rewards across stimulus domains.Neuropsychopharmacology accepted article preview online, 15 March 2017. doi:10.1038/npp.2017.58.

Language: en