Action naming in Parkinson's disease patients on/off dopamine

Growing evidence supports the notion that the same brain areas involved in planning and execution of movements are also involved in verb processing. Recent studies have pointed out the existence of verb impairment in patients with Parkinson's disease (PD), a neurodegenerative disorder typically characterized by motor disturbance related to dopamine deficiency in the nigrostriatal system. The aim of this study was to test the influence of dopaminergic treatment in a group of non-demented PD patients on the performance of action naming. The action pictures belonged to two categories: pictures with high and low degree of motor content. A group of 20 PD patients without dementia and 15 controls performed the task. PD patients were assessed twice, on and off medication, controls only once. A repeated measures ANOVA was carried out on the reaction times. The results showed a main effect of group and a significant interaction between group×motor content when comparing the three groups. When the comparison was made only on the PD groups (on vs. off medication) the interaction group×motor content was also significant, indicating that PD patients off medication had longer reaction times for pictures with a high degree of motor content compared to PD patients on medication. These results suggest a selective deficit in naming pictures associated with high motor content in PD patients without dopamine medication. This effect could be due to the relations between brain motor areas and verb processing associated with dopamine depletion.