Altered Neural Reward Representations in Pathological Gamblers Revealed by Delay and Probability Discounting

CONTEXT: The neural basis of excessive delay discounting and reduced risk sensitivity of pathological gamblers with a particular focus on subjective neural reward representations has not been previously examined. OBJECTIVE: To examine how pathological gamblers represent subjective reward value at a neural level and how this is affected by gambling severity. DESIGN: Model-based functional magnetic resonance imaging study with patients and control subjects. SETTING: Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf. PARTICIPANTS: Participants were recruited from the local community by advertisement and through self-help groups. A sample of 16 pathological gamblers (according to the DSM-IV definition) was matched by age, sex, smoking status, income, educational level, and handedness to 16 healthy controls. RESULTS: Pathological gamblers showed increased discounting of delayed rewards and a trend toward decreased discounting of probabilistic rewards compared with matched controls. At the neural level, a significant group × condition interaction indicated that reward representations in the gamblers were modulated in a condition-specific manner, such that they exhibited increased (delay discounting) and decreased (probability discounting) neural value correlations in the reward system. In addition, throughout the reward system, neuronal value signals for delayed rewards were negatively correlated with gambling severity. CONCLUSIONS: The results extend previous reports of a generally hypoactive reward system in pathological gamblers by showing that, even when subjective reward valuation is accounted for, gamblers still show altered reward representations. Furthermore, results point toward a gradual degradation of mesolimbic reward representations for delayed rewards during the course of pathological gambling.