Objective: To study EEG oscillatory activity associated to reward prediction error in Parkinson’s disease (PD) patients with impulse control disorders (ICD) and determine how dopaminergic therapy modulate this activity.

Background: PD patients display deficits in using information about potential incentives (and punishments) or by processing the consequences associated with own decision making. It has been suggested that aberrant computation of reward prediction errors (unexpected wins/loss) might underlie ICD in PD. The different spectral components of the EEG reflect dissociated cortical processes associated to the valence and predictability of the feedback.

Methods: Eight patients with ICD (EP + ICD), 13 without ICD (EP-TCI) and 10 healthy controls participated in this study. Patients were assessed under dopaminergic agents (“on” state) and after dopaminergic agent withdrawal (“off”). Participants performed a risk decision-making task whose probabilities of reward gain and loss were predefined; the congruence between the decision made and the valence of the outcome was manipulated (degree of consistency with the decision in 70% of the cases). During the performance of the task the EEG was recorded and the spectral components were determined in the time-frequency domain using multitaper methods.

Results: Analysis all-conditions all-groups time-frequency maps revealed an increase in theta (4-7 Hz) power between 250-450ms after the feedback presentation. A significant attenuation in low-beta power (13-18 Hz), appeared later (400-600 ms). Separated by conditions, group-level comparisons showed higher theta power associated to unexpected losses in EP+ICD patients, as compared with EP-ICD and controls. This component was modulated by dopaminergic agents only in the EP+ICD group; higher theta associated with ON state only in the +ICD whereas, no change of theta associated with the OFF state. Significant positive correlation between this post-feedback theta activity and trait impulsivity was detected.

Conclusions: Our results suggest an impairment in the processing of reward expectation and prediction error in PD patients with ICD. Increased theta-band activity time-locked to unexpected outcomes seems to be modulated by dopaminergic agents in PD patients with ICD, showing a dissociate effect depending upon feedback valence. This modulation appears higher in subjects with high impulsivity.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/dissociate-effect-of-dopaminergic-therapy-in-reward-expectation-and-prediction-error-in-pd-patients-with-comorbid-impulse-control-disorder/