In 1996 neuroscientist Giacomo Rizzolatti and his co-workers at the University of Parma in Italy published some remarkable findings. They had run an experiment to record electrical activity from neurons specialized for hand movement in two pigtail macaques. As anticipated, these neurons fired when the animals reached for peanuts placed in front of them. What was entirely unexpected, however, was that these same neurons fired when a scientist in the lab reached for the nuts instead. The monkey remained stationary. Nevertheless, watching the scientist move had activated motor areas in the macaques brain, just as if the animal had carried out the action itself.
Using functional magnetic resonance imaging (fMRI), Rizzolatti and his colleagues soon documented the same phenomenon in humans and dubbed the responsible nerve cells "mirror neurons" [see "A Revealing Reflection," by David Dobbs; Scientific American Mind, April/May 2006]. These cells look like any other neuron but boast a surprising double function: they become active during any type of directed behavior--chewing food, throwing a ball, performing a dance--whether we do it ourselves or simply watch someone else do it. Indeed, our conscious brain generates an inner simulation of sorts when we follow the actions of another person. Mirror neurons are presumed to be abundant in brain regions responsible for planning and initiating actions, including the primary motor cortex, the premotor cortex and supplementary motor areas.