Mirror neurons are a special class of neuron whose key role in language acquisition and learning social behavior has recently been established. Mirror neurons have been observed, in monkeys and humans, to fire both during the performance of a particular behavior, and when the subject is only thinking about the behavior. They also fire when observing someone else perform the action in question, providing evidence that they are instrumental in the brain's ability to learn through observation, a characteristic of social behavior that has long been known to exist.
Presumably, mirror neurons, by firing both during the observation of an action and the process of thinking about an action, set up circuits in the brain that can then be replayed in acting out the behavior in question.
Mirror neurons could go a long way toward explaining the amazing phenomenon pro-basketball players and other athletes call being "in the zone." Many players have said that when they are "in the zone," they can see the whole court, know exactly where the ball is at all times, and can't miss when they shoot.
A recent study by UCLA neuroscientist Daniel Glaser found that skilled dancer's mirror neuron systems lit up far more than those of non-dancers while watching a dance performance, suggesting that their brains were simulating their learned-ability solely through the act of observation.
The brain's ability to replay learned skills even while the body is immobile may be a key factor in the ability of surfers, musicians, and other athletes besides basketball players, to get "in the zone."