Müller, Erik Malte
0000-0002-8721-8963 Research Projects
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Müller
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Erik Malte
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Research Data Open Access Modeling Reward Learning Under Placebo Expectancies: A Q-Learning Approach(2022-05-10) Augustat, Nick; Müller, Erik Malte; Endres, Dominik; Chuang, Li-Ching; Panitz, Christian; Stolz, ChristopherResearch Data Open Access Uncertainty of treatment efficacy moderates placebo effects on reinforcement learning(Philipps-Universität Marburg) Augustat, Nick; Endres, Dominik; Müller, Erik MalteThis repository includes code and data necessary for running the online survey and task, and the analyses of the manuscript "Augustat, N., Endres, D., Müller, E. M.: Uncertainty of treatment efficacy moderates placebo effects on reinforcement learning". Abstract: The placebo-reward hypothesis postulates that positive effects of treatment expectations on health (i.e., placebo effects) and reward processing share common neural underpinnings. Moreover, experiments in humans and animals indicate that reward uncertainty increases striatal dopamine, which is presumably involved in placebo responses and reward learning. Therefore, treatment uncertainty, analogously to reward uncertainty, may affect reward learning after placebo treatment. Here, we address whether different degrees of uncertainty regarding the efficacy of a sham treatment affect reward learning. In an online between-subjects experiment with N=141 participants, we systematically varied the provided efficacy instructions before participants first received a sham treatment that consisted of listening to binaural beats and then performed a probabilistic reinforcement learning task. We fitted a Q-learning model including two different learning rates for positive (gain) and negative (loss) reward prediction errors and an inverse gain parameter to behavioral decision data in the reinforcement learning task. Our results yielded an inverted-U-relationship between provided treatment efficacy probability and learning rates for gain, such that higher levels of treatment uncertainty, rather than of expected net efficacy, affect presumably dopamine-related reward learning. These findings support the placebo-reward hypothesis and suggest harnessing uncertainty in placebo treatment for recovering reward learning capabilities.Research Data Open Access Dopamine D2 receptor antagonism modulates antidepressant placebo effects on reward sensitivity in healthy participants(Philipps-Universität Marburg) Augustat, Nick; Lee, Eunhwi; Ahn, Woo-Young; Chuang, Li-Ching; Endres, Dominik; Müller, Erik MalteContent: Open code and data for the manuscript "Augustat, N., Lee, E., Ahn, W. Y., Chuang, L. C., Endres, D., Mueller, E.: Dopamine D2 receptor antagonism modulates antidepressant placebo effects on reward sensitivity in healthy participants". Instructions can be found in the file "readme.txt", and a preprint in the file "RL_Manuscript.tar". Summary: The data set consists of 272 participants allocated in a 2x2 between-subjects design (expectation: high/low, substance: placebo/sulpiride 400mg) who performed a probabilistic selection task. We fit a total of 74 hierarchical Bayesian reinforcement learning models with different sets of parameters to participants' choice data and conducted a model comparison, including recovery checks, across all models. The winning model consisted of three parameters (learning rate, inverse temperature, forgetting rate) and yielded an increase in learning rates under high expectations in the placebo group but not in the sulpiride group. Higher learning rates may indicate an increase in reward sensitivity, suggesting an expectation-induced improvement in reward sensitivity. Sulpiride 400mg blocked this effect, supporting a modulatory role of dopamine.