Multiple neural representations of object-directed action in an imitative context.

Object-directed action consists of aspects that range from low-level kinematic patterns to high-level action goals. Although previous studies have suggested that the human mirror neuron system (MNS) is involved in understanding or imitating an observed action, it is unclear precisely which levels of action representation are reflected in MNS activity. In this study, we used an imitation-matching task, which is previously used in behavioral experiments for infants, and fMRI to reveal the neural basis for imitation of multiple representations of observed actions. In our experiment, two video footages showing a pen being grasped and placed into one of two cups were sequentially presented. The participants judged whether an actor's action in the first movie was correctly imitated by an imitator in the second movie, regarding the following four aspects: action goal, a means of manipulation, an effector used, and movement trajectory. Although identical sets of stimuli were presented, different brain regions were activated, depending on the matching judgments made by subjects between the two actions. The current study indicates that distinct brain regions are involved in recognition of multiple aspects of transitive actions, which is largely consistent with a visuomotor circuit of action production by the observer.