Levodopa effect on spontaneous speech in Parkinson's disease

Parkinson's disease (PD) is associated with verb deficits detected with tasks including picture naming and verbal fluency. However, these deficits are not frequently reported by the patients themselves. Levodopa, the gold standard for motor symptoms in PD, has been previously implicated to improve these verb deficits. We evaluated the effect of levodopa by using a spontaneous speech task which is more naturalistic than the previously used tasks to detect verb deficits. Thirty PD patients, and 30 age-, gender-, years of education-matched healthy controls were included. Patients were tested while motor 'on' and 'off. Levodopa did not affect spontaneous speech, although it improved the motor symptoms. Compared to controls, PD patients produced shorter and a lower number of sentences. The verb deficit was independent of cognitive or motor performance. The pathophysiology of motor symptoms and verb deficits most likely differ, and levodopa does not improve verb deficits during spontaneous speech.