Dopaminergic medication counteracts conflict adaptation in patients with Parkinson's disease

OBJECTIVE: We tested the role of dopamine in conflict-induced behavioral adjustments by evaluating the effect of dopaminergic medication on conflict adaptation in Parkinson's disease (PD) patients.

METHOD: Nine PD patients performed a vocal Stroop task on two separate testing occasions: once on their regular medication and once after overnight withdrawal.

RESULTS: In line with previous studies (e.g., Bonnin, Houeto, Gil, & Bouquet, 2010), patients displayed no conflict adaptation when tested on medication. However, the same patients tested off of their medication did display a conflict adaptation effect in that the size of the interference effect was reduced after incongruent trials compared with after congruent trials.

CONCLUSIONS: This difference is discussed in terms of an inverted U-shaped relation between dopamine and performance, according to which dopaminergic medication has detrimental effects on PD patients' performance by overdosing brain regions that are relatively spared in the initial stage of the disease, including the ventral striatum and prefrontal cortex.