Verbal fluency in Parkinson's disease patients on/off dopamine medication.

INTRODUCTION: Parkinson's disease (PD) is associated with dopamine depletion in the fronto-striatal network which affects some language aspects such as verb processing. Some experiments have demonstrated that dopamine deficiency plays a role in the normal functioning of the lexico-semantic system. As a result, the verbal fluency task could be a useful tool to assess the function of the semantic system, by examining both the number of words generated and the frequency of use of those words.
OBJECTIVE: The aim of this study was to find out how dopamine affects the performance of PD patients using a verbal fluency task, focussing on action-word fluency.
METHOD: A group of 20 PD patients and 20 controls participated in the study. Participants were assessed with four different verbal fluency tasks: phonological, semantic (animal and supermarket words) and action fluency. PD patients were tested twice (on/off medication) and controls only once.
RESULTS: For the number of words, there were significant differences between PD patients on and off medication in the phonological and action fluency tasks. Compared to controls, PD off medication produced significantly fewer words in phonological, and actions. Regarding frequency, differences were found between PD patients off medication and controls for the action-word category. DISCUSSION: Our data showed a specific deficit in PD patients off medication in categories mainly depending on frontal lobe function (phonological and actions) while these differences were restored with dopamine treatment. Moreover, PD patients off medication produced higher frequency verbs than controls, suggesting that dopamine affects the normal functioning within the lexico-semantic network of verbs.