The role of the basal ganglia in action imitation: neuropsychological evidence from Parkinson's disease patients

Though previous studies have suggested that the basal ganglia are necessarily involved in action imitation, their precise role is unclear. An important source of evidence concerns patients with Parkinson's disease (PD) who suffer basal ganglia impairments. Some studies report poor execution of observed meaningful (MF) transitive (tool-related) actions but normal performance with intransitive (non-tool-related) MF and meaningless (ML) actions (Leiguarda et al. in Brain 120:75-90, 1997; Leiguarda 2001 in Neuroimage 14:137-141). In other cases, though, patients with lesions involving the basal ganglia appear impaired in imitating ML as compared to meaningful MF transitive pantomimes. Here, we tested a group of PD patients in a full 2 x 2 design with MF transitive and intransitive pantomimes and matched ML movements. PD patients generated higher scores when imitating MF transitive actions than ML-matched actions. On the other hand, ML than MF intransitive actions did not differ significantly. The performance of the patients on imitating ML transitive actions also correlated with their performance on the Corsi block test of visuospatial memory and their scores at the test of verbal fluency for phonemic categories (FAS) while MF intransitive actions correlated with FAS and the neurological evaluation (UPDRS) The results are discussed in terms of the factors that load on visual memory for action reproduction, as well as the possible role of the basal ganglia in communicative actions (for MF intransitive actions).