Social Cognitive and Affective Neuroscience Advance Access originally published online on September 18, 2006
Social Cognitive and Affective Neuroscience 2007 2(1):20-30; doi:10.1093/scan/nsl021
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Individual differences and the neural representations of reward expectation and reward prediction error
Department of Epilepsy, University of Bonn, Sigmund-Freud-Str. 25, Bonn 53105, Germany and Department of Psychology and Center for Neuroscience, University of California, Davis, CA 95616, USA
Reward expectation and reward prediction errors are thought to be critical for dynamic adjustments in decision-making and reward-seeking behavior, but little is known about their representation in the brain during uncertainty and risk-taking. Furthermore, little is known about what role individual differences might play in such reinforcement processes. In this study, it is shown behavioral and neural responses during a decision-making task can be characterized by a computational reinforcement learning model and that individual differences in learning parameters in the model are critical for elucidating these processes. In the fMRI experiment, subjects chose between high- and low-risk rewards. A computational reinforcement learning model computed expected values and prediction errors that each subject might experience on each trial. These outputs predicted subjects’ trial-to-trial choice strategies and neural activity in several limbic and prefrontal regions during the task. Individual differences in estimated reinforcement learning parameters proved critical for characterizing these processes, because models that incorporated individual learning parameters explained significantly more variance in the fMRI data than did a model using fixed learning parameters. These findings suggest that the brain engages a reinforcement learning process during risk-taking and that individual differences play a crucial role in modeling this process.
Keywords: reward prediction error; reward expectation; fMRI; decision-making; reinforcement learning; risk-taking
Correspondence should be addressed to: Michael X Cohen, Department of Epilepsy, University of Bonn, Sigmund-Freud-Str. 25, Bonn 53105, Germany. E-mail: mcohen{at}ucdavis.edu
Received May 11, 2006. Accepted August 8, 2006.