Scientists have recently discovered that neurons in the premotor area that fire in preparation for upcoming movements also fire when we observe someone else carry out that action (Meltzoff and Prinz, 2002). Common brain regions thus process both the perception and production of a movement. The infant's observation of her parent's projecting tongue fires the premotor neurons that represent her tongue and this priming activates the related motor cortex neurons that project her tongue out in mimicry.

We experience this mimicking phenomenon most commonly when we see someone yawn, and then typically have to stifle our own yawn. Since infants must learn many movements, they don't inhibit the mimicking of movements they observe. For them it's monkey see, monkey do (and it's interesting that the initial mirror neuron research was done on monkeys).

Our mirror neurons won't fire at the mere observation of a hand or mouth – only when its carrying out a goal directed action. Further, they will respond to a hand but not a tool that's grasping or moving an object (since body parts and not tools are represented in our motor/premotor areas).

Mirror neurons may thus facilitate the preliminary motor neuron simulation, priming, programming, and rehearsing that occurs in children, and this process obviously enhances our eventual mastery of complex motor behaviors, and our ability to read the minds of others. For example, inferring the potential movements of others is an essential skill in many games in which players try to fake out opponents. Mirror neuron stimulation may also explain why so many people enjoy observing the movements of virtuoso athletes, dancers, and musicians. It allows us to mentally represent actions we can't physically mimic. Note the related active body language of former athletes as they observe a game they once played.