Hemisphere asymmetries for imitation of novel gestures

Background: Disorders of imitation are traditionally considered as a symptom of apraxia, but defective imitation of gestures can contrast with intact performance of gestures to verbal command and vice versa. It thus seems worthwhile to explore the neural basis of imitation of gestures independently of other manifestations of apraxia. Objective: To assess body part specificity of disturbances of imitation for meaningless gestures of fingers, hand, and foot. Method: Imitation of meaningless gestures involving fingers (internal hand configuration), hand (external hand position), or foot was examined in 30 patients with left brain damage (LBD), 20 patients with right brain damage (RBD), and 20 normal control subjects. Results: LBD affected imitation of hand and foot gestures more than imitation of finger gestures, whereas RBD had the strongest effect on finger gestures and affected foot gestures more than hand gestures. Conclusion: These results can be accounted for by the assumption that body part coding of gestures depends on left hemisphere function and that additional right hemisphere contributions are afforded when demands on perceptual discrimination rise.