From Wikipedia

Responsive Brain

A mirror neuron is a neuron that fires both when an animal acts and when the animal observes the same action performed by another. Thus, the neuron "mirrors" the behavior of the other, as though the observer were itself acting. Such neurons have been directly observed in primates, and are believed to occur in humans and other species including birds. In humans, brain activity consistent with that of mirror neurons has been found in the premotor cortex and the inferior parietal cortex.

Some scientists consider mirror neurons one of the most important recent discoveries in neuroscience. Among them is V.S. Ramachandran, who believes they might be very important in imitation and language acquisition. However, despite the popularity of this field, to date no widely accepted neural or computational models have been put forward to describe how mirror neuron activity supports cognitive functions such as imitation.

The function of the mirror system is a subject of much speculation. Many researchers in cognitive neuroscience and cognitive psychology consider that this system provides the physiological mechanism for the perception action coupling (see the common coding theory). These mirror neurons may be important for understanding the actions of other people, and for learning new skills by imitation. Some researchers also speculate that mirror systems may simulate observed actions, and thus contribute to theory of mind skills, while others relate mirror neurons to language abilities. It has also been proposed that problems with the mirror system may underlie cognitive disorders, particularly autism. However the connection between mirror neuron dysfunction and autism remains speculative and it is unlikely that mirror neurons are related to many of the important characteristics of autism.