Uncertainty about mapping future actions into rewards may underlie performance on multiple measures of impulsivity in behavioral addiction: evidence from Parkinson's disease.

A subset of patients with Parkinson's disease (PD) develops behavioral addictions, which may be due to their dopamine replacement therapy. Recently, several groups have been comparing PD patients with and without behavioral addictions on tasks that are thought to measure aspects of impulsivity. Several of these experiments, including information sampling, a bias toward novel stimuli and temporal discounting, have shown differences between PD patients with and without behavioral addictions. We have developed a unifying theoretical framework that allows us to model behavior in all three of these tasks. By exploring the performance of the patient groups on the three tasks with a single framework, we can ask questions about common mechanisms that underlie all three. Our results suggest that the effects seen in all three tasks can be accounted for by uncertainty about the ability to map future actions into rewards. More specifically, the modeling is consistent with the hypothesis that the group with behavioral addictions behaves as if they cannot use information provided within the experimental context to improve future reward guided actions. Future studies will be necessary to more firmly establish (or refute) this hypothesis. We discuss this result in light of what is known about the pathology that underlies the behavioral addictions in the PD patients.