An EEG marker of reward processing is diminished in Parkinson’s disease

•Dopamine neuron cell death leads to a host of deficits in Parkinson’s disease.•The reward positivity is theorized to be dependent on dopaminergic function.•The reward positivity was blunted in people with Parkinson’s disease. The electroencephalographic signal known as the Reward Positivity (RewP) scales with the reward prediction error following reward receipt. This signal is computationally identical to the dopamine-driven learning process relating to the discrepancy between reward expectation and reward acquisition. The current study aimed to investigate if the RewP is diminished in Parkinson’s disease (PD). In this study, 28 people with PD and 28 age- and sex-matched healthy controls completed a reinforcement-learning task. In line with expectations, the RewP was smaller in persons with PD than in controls. Yet contrary to expectations, RewP amplitude did not differ in on vs. off medication conditions, and it was positively correlated with the number of years diagnosed with PD. We propose that this symptom-specific alteration in RewP may be a consequence of a common methodological procedure in PD research (e.g. restricted recruitment) or it might truly be a marker of early-stage disease (e.g. prior to network re-adaptation). These surprising findings motivate separate testable hypotheses for assessing aspects of PD with this novel neural marker of reward.