Impulse control disorder in Parkinson's disease is associated with abnormal frontal value signalling.

This article investigates how dopaminergic medication affects reinforcement learning (RL) in early-stage Parkinson's disease (PD) patients, focusing on individual variability related to comorbid impulse control disorders (ICDs) and depression. Using functional MRI and a probabilistic instrumental learning task in 199 PD patients (138 ON medication, 61 OFF medication) and 59 healthy controls, the study found that medication-induced shifts favoring gain over loss learning occurred primarily in patients with ICDs, accompanied by increased expected value (EV) signaling in the ventromedial prefrontal cortex (vmPFC), without changes in striatal reward prediction error (RPE) signaling. These results suggest that dopaminergic medication effects on RL in PD are modulated by ICD presence and reflect altered value computation in medial frontal cortex rather than striatal learning signals. No significant medication-related effects were observed in relation to depression, highlighting ICD as a key factor in the heterogeneity of dopaminergic medication responses in PD.