Everyone has had the experience of watching a film such as Indiana Jones surrounded by snakes or of Dr. No where a spider crawls up James Bond arm or of someone cutting themselves and of putting oneself in the other's shoes and experiencing their feelings. We size up friends, acquaintances, and learn from others by using this social skill. How is this accomplished?
In 1992 Giacomo Rizzolatti and colleagues were studying macaque monkeys by implanting electrodes in their ventral premotor cortex used to control hand and mouth movements. Serendipitously as a member of the team reached for his own lunch he noticed that the monkey's neurons began to fire in the premotor cortex,i.e., the same firing pattern when the monkey made the same hand movement. Yet, the monkey was just sitting there. This was the initial discovery of mirror neurons - neurons that fire when a certain action is performed and also when that action is observed.
This is an extraordinarily important discovery. More recent studies have broadened the findings that neurons mirror movement to neural activity mirrors intentions, sensations, and emotions. Abnormalities of the mirror system are found in autistic individuals who are impaired in the social fields - understanding and empathizing with others. Might this also yield insight into other disorders with social impairment or even provide a new theory of the development of language?
The human frontal region is homologous to the F5 region Rizzolatti et.al. studied in the macaque monkeys. He has postulated that mirror neurons in this area could improve the imitation of hand and mouth movements used in communication. This is important in an infants acquisition of language. Iacoboni and colleagues at UCLA have shown that listening to speech activates those neurons used to produce speech. Additional work by both groups has shown a different pattern of mirror response depending on the intention of the action such as grasping food to eat versus grasping food to place in a container. It was also shown that this pattern was identical when the monkeys observed the actions. This suggests that mirror neurons take into account the context in predicting the next action.
Iacoboni and colleagues have also demonstrated that certain areas of the frontal cortex are activated when looking at or making emotional facial expressions. Other investigators, Keysers and colleagues, put masked subjects into a fMRI scanner and exposed them to noxious odors and they found that the insula was activated. This same area was activated when subjects were shown pictures of people displaying the emotion of disgust.
All of these observations are central to developing more complete ideas about empathy, imitation, language development, and the actions and emotions of others.