Does the end justify the means? A PET exploration of the mechanisms involved in human imitation.

Imitation is a natural mechanism involving perception-action coupling which plays a foundational role in human development, in particular to extract the intention from the surface behavior exhibited by others. The aim of this H(15)(2)O PET activation experiment was to investigate the neural basis of imitation of object-oriented actions in normal adults. Experimental conditions were derived from a factorial design. The factors were: (a) is the stimulus event shown to subjects during observation of the model and (b) is the response manipulation performed by the subject. Two key components of human action, the goal and the means to achieve it, were systematically investigated. The results revealed partially overlapping clusters of increased regional cerebral blood flow in the right dorsolateral prefrontal area and in cerebellum when subjects imitated either of the two components. Moreover, specific activity was detected in the medial prefrontal cortex during the imitation of the means, whereas imitating the goal was associated with increased activity in the left premotor cortex. Our results suggest that for normally functioning adults, imitating a gesture activates neural processing of the intention (or goal) underlying the observed action.