Does Parkinson's disease affect verb production in picture descriptions?

Research on Parkinson's disease (PD) has documented significant deficits in verb production, with more robust results in single word retrieval tasks than in connected speech, yet the underlying causes of these deficits are disputable, especially concerning connected speech production. We analyzed picture descriptions provided by 48 individuals with PD and 48 age-matched healthy controls, and examined the percent of nouns and verbs of all words, the number of described events, verbs denoting activity, verbs in active morpho-syntactic patterns, and transitive verbs. Individuals with PD produced a lower percent of verbs than did control participants, but the groups differed in no other variable. Scores on a cognitive screening task associated with the percent of verbs and the number of events. We suggest that verb retrieval in connected speech in PD reflects no specific difficulty with action semantics, but rather the spread of PD pathology into more diffuse verb-specific neural networks.