Dopamine supports sentence comprehension in Parkinson's Disease

Objective: To determine the role of dopamine in the executive resource comp onent of sentence comprehension. Methods: We studied sentence-picture match ing in 20 right-handed, non-demented, native English speakers with mild Par kinson's disease (PD) when 'on' and 'off' their levodopa, taking into accou nt 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 demonstrate d 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 i mpaired comprehension of grammatically complex sentences when 'off' levodop a was associated with poorer performance on foils requiring working memory resources. Performance on an independent measure of verbal working memory c orrelated 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.