The Neural Basis of Imitation is Body Part Specific

Imitation is an important constituent of the behavioral repertoire of human beings. We use imitation for learning motor skills, for facilitating comprehension of other persons' actions and mental states, and as a communicative reference to actions or people. Although some non-human species display imitative behaviors, none of them equals the versatility and perfection of human imitation. The versatility and apparent ease of human imitation is, however, not at all self-evident when one considers the neural and cognitive transformations that must be accomplished for successful imitation. Imitation of meaningless gestures poses a particular challenge for our brain, because similarity between the body of the model and one's own body must bridge fundamental differences between the perspective and modalities of perceiving and controlling one's own and other bodies. We analyzed the locations of left-hemisphere lesions disturbing imitation of meaningless gestures and found a clear-cut body part specificity. Disturbed imitation of finger postures was associated with anterior lesions including the opercular portion of the inferior frontal gyrus, whereas disturbed imitation of hand postures was associated with posterior lesions affecting the inferior parietal lobule and temporo-parieto-occipital junction. These locations do not correspond with known somatotopic maps of motor representations. Rather, they argue for an intermediate step of processing interpolated between perception and execution of gestures as has been suggested by the mirror neuron and the body part coding hypotheses.