Human ability to imitate movements is instantiated in parietal, premotor and opercular structures, often referred to as the human homologue of the macaque mirror neuron system. As most studies employed imitation of specular models (participants imitated the seen movement as their mirror reflection), it is unclear whether the structures implicated code for the anatomical compatibility between the performer and the model or the spatial compatibility between the location at which both movements occur. We used fMRI to disentangle the neural mechanisms underlying anatomical and spatial components of imitation. Participants moved one finger which was either spatially or anatomically compatible with the finger moved in a video-display. In keeping with the existent behavioral literature, we found that during the spatial task, participants' responses were faster when the seen movement was also anatomically compatible, whereas in the anatomical task, responses were faster when the seen movement was also spatially compatible. Critically, the activity of the parietal opercula bilaterally was associated with the anatomical compatibility effect. Furthermore, increased activity of the left middle frontal gyrus and right superior temporal sulcus (extending to the temporo-parietal junction) was found in those trials in which the spatial mapping between the seen and executed movements was detrimental for the anatomical task. Our findings extend current understanding of the role played by spatial and anatomical components in imitation and provide new insights about the parietal opercula.
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