Mirror Neuron

A mirror neuron (e.g. Gallese et al., 1996) is a neuron in motor cortex that responds when an agent performs a certain action, but also responds when the agent observes some other agent perform the same action. They were accidentally discovered when researchers were recording from motor neurons in a monkey's brain that were associated with hand and mouth movements. “Then we began to notice something strange:  when one of us grasped a piece of food, the monkeys’ neurons would fire in the same way as when the monkeys themselves grasped the food” (Rizzolatti, 2006, p. 56).

Mirror neurons are an important discovery in neuroscience. They are possibly an instantiation of the simulation theory of person perception. They have also been argued to be related to autism -- some researchers suggest that autism results when the human mirror neuron system is not working properly (e.g. Williams et al., 2001).

References:

1. Gallese, V., Fadiga, L., Fogassi, L., & Rizzolatti, G. (1996). Action recognition in the premotor cortex. Brain, 119, 593-609.
2. Rizzolatti, G., Fogassi, L., & Gallese, V. (2006). Mirrors in the mind. Scientific American, 295(5), 54-61.
3. Williams, J. H. G., Whiten, A., Suddendorf, T., & Perrett, D. I. (2001). Imitation, mirror neurons and autism. Neuroscience and Biobehavioral Reviews, 25(4), 287-295.

(Added November 2009)