When mirroring is not enough: that is, when only a complementary action will do (the trick).

It is well known that perceiving another person's body movements activates corresponding motor representations in an observer's brain, a process which appears to be imitative in nature. However, it is also true that simply imitating another person's action/s in many situations is not an effective or appropriate response, as successful interaction often requires complementary rather than emulative behavior. This manuscript presents a review of the recent efforts to identify the mechanisms responsible--once observed actions have been mapped onto an observer's motor system--for the switch from the tendency to imitate actions to the inclination to carry out a nonidentical context-appropriate response. The putative human mirror neuron system seems to play a particularly important role in this process because of its prominent function in action observation and execution. Recent findings indicate, however, that acting in a complementary fashion might entail the recruitment of neural systems outside of the human mirror neuron system.