Simulation theory of empathy is a theory that holds that humans anticipate and make sense of the behavior of others by activating mental processes that, if carried into action, would produce similar behavior. This includes intentional behavior as well as the expression of emotions. The theory states that children use their own emotions to predict what others will do. Therefore, we project our own mental states onto others.Simulation theory is not primarily a theory of empathy, but rather a theory of how people understand others—that they do so by way of a kind of empathetic response. This theory uses more biological evidence than other theories of mind, such as the theory-theory. Simulation theory of empathy is a theory that holds that humans anticipate and make sense of the behavior of others by activating mental processes that, if carried into action, would produce similar behavior. This includes intentional behavior as well as the expression of emotions. The theory states that children use their own emotions to predict what others will do. Therefore, we project our own mental states onto others.Simulation theory is not primarily a theory of empathy, but rather a theory of how people understand others—that they do so by way of a kind of empathetic response. This theory uses more biological evidence than other theories of mind, such as the theory-theory. Simulation theory is based in philosophy of mind, a branch of philosophy that studies the nature of the mind and its relationship to the brain, especially the work of Alvin Goldman and Robert Gordon. The discovery of mirror neurons in macaque monkeys has provided a physiological mechanism for the common coding between perception and action (see Wolfgang Prinz) and the hypothesis of a similar mirror neuron system in the human brain.Since the discovery of the mirror neuron system, many studies have been carried out to examine the role of this system in action understanding, emotion and other social functions. Mirror neurons are activated both when actions are executed and the actions are observed. This unique function of mirror neurons may explain how people recognize and understand the states of others; mirroring observed action in the brain as if they conducted the observed action. Two sets of evidence suggest that mirror neurons in the monkey have a role in action understanding. First, the activation of mirror neurons requires biological effectors such as hand or mouth. Mirror neurons do not respond to the action with tools like pliers. Mirror neurons respond to neither the sight of an object alone nor an action without an object (intransitive action). Umilta and colleagues demonstrated that a subset of mirror neurons fired when final critical part of the action was not visible to the observer. The experimenter showed his hand moving toward a cube and grasping it, and later showed the same action without showing later part grasping the cube (placing the cube behind the occluder). Mirror neurons fired on both visible and invisible conditions. On the other hand, mirror neurons did not discharge when the observer knew that there was not a cube behind the occluder. Second, responses of mirror neurons to same actions are different depending on context of the action. A single cell recording experiment with monkeys demonstrated the different level of activation of mouth mirror neurons when monkey observed mouth movement depending on context (ingestive actions such as sucking juice vs. communicative actions such as lip-smacking or tongue protrusions). An fMRI study also showed that mirror neurons respond to the action of grasping a cup differently depending on context (to drink a cup of coffee vs. to clean a table on which a cup was placed).