Dopamine supports sentence comprehension in Parkinson's Disease

Objective: To determine the role of dopamine in the executive resource component of sentence comprehension. Methods: We studied sentence-picture matching in 20 right-handed, non-demented, native English speakers with mild Parkinson's disease (PD) when 'on' and 'off' their levodopa, taking into account disease duration to control for endogenous dopamine metabolism. We also administered a verbal working memory measure that does not involve specific grammatical manipulations. Results: PD patients 'off' levodopa demonstrated a significant discrepancy in their comprehension of grammatically complex sentences compared to grammatically simpler sentences that was not evident when PD patients were 'on' levodopa. An error analysis demonstrated that impaired comprehension of grammatically complex sentences when 'off' levodopa was associated with poorer performance on foils requiring working memory resources. Performance on an independent measure of verbal working memory correlated only with comprehension of grammatically complex sentences during levodopa supplementation, but working memory according to this measure did not differ during 'on' and 'off' states. Conclusion: Dopamine supports the executive resources contributing to sentence comprehension in PD. (C) 2001 Elsevier Science B.V. All rights reserved.