Giovanni Buccino,a,* Ferdinand Binkofski,b and Lucia Riggioa a Dipartimento di Neuroscienze, Sezione di Fisiologia, Universita di Parma, Via Volturno 39, 43100 Parma, Italy
Mirror neurons, first described in the rostral part of monkey ventral premotor cortex (area F5), discharge both when the animal performs a goal-directed hand action and when it observes another individual performing the same or a similar action. More recently, in the same area mirror neurons responding to the observation of mouth actions have been also found. In humans, through an fMRI study, it has been shown that the observation of actions performed with the hand, the mouth and the foot leads to the activation of different sectors of Brocas area and premotor cortex, according to the effector involved in the observed action, following a somatotopic pattern which resembles the classical motor cortex homunculus. These results strongly support the existence of an execution-observation matching system (mirror neuron system). It has been proposed that this system is involved in action recognition. Experimental evidence in favor of this hypothesis both in the monkey and humans are shortly reviewed.
Action recognition is a fundamental step on which social behavior depends. Although numerous hypotheses have been forwarded to explain action recognition (see Barresi & Moore, 1996), two main theories may explain this cognitive function (Rizzolatti, Fogassi, & Gallese, 2001). The first one, often referred as the ‘‘visual hypothesis’’, maintains that action recognition relies on a visual analysis of all constituents of a specific action, that is a visual analysis of the effector involved, of the object on which the action is acted upon, and finally,of the context in which the action is going on. Inference about the interactions between all these elements visually described would allow the observer to understand and recognize actions performed by others. If this hypothesis were true, the neural substrates involved in action recognition would be the visual extrastriate areas, the inferotemporal lobe and the superior temporal sulcus region. The second one, referred as the ‘‘direct-matching hypothesis’’, maintains that one can recognize actions performed by others by mapping the observed action on his/her own motor representation of the observed action. According to this hypothesis, action observation automatically activates in the observer the same neural structures involved in the actual execution of the observed action. Since the result of the activation of these neural substrates during action execution is known, the activation of the same substrates during action observation would allow the observer, through an observation–execution matching mechanism, to understand what the actor is doing. This latter hypothesis has recently found a strong neurophysiological support in the discovery of the mirror neuron system. This review will focus on the organization of the mirror neuron system both in the monkey and humans, and on the experimental evidence of its involvement in action observation and recognition.