Deactivation in the sensorimotor area during observation of a human agent performing robotic actions.

It is well established that several motor areas, called the mirror-neuron system (MNS), are activated when an individual observes other's actions. However, whether the MNS responds similarly to robotic actions compared with human actions is still controversial. The present study investigated whether and how the motor area activity is influenced by appearance (human vs. robot) and/or kinematics (human vs. robot) of the observed action using near-infrared spectroscopy. The results showed that there was a strong interaction between these factors, revealing strong deactivations in sensorimotor areas when the subject saw a human agent performing robotic actions, which was significantly different from responses when observing the human agent acting in a human way and the robot agent performing robotic actions. These results indicate that MNS activity is sensitive to congruency between the appearance and kinematics of the agent, especially when the agent has a human appearance. We discuss the experience-dependent characteristics of MNS sensitivity to observed actions.