A model of fear and pain is presented in which the two are assumed to activate totally different classes of behavior. Fear, produced by stimuli that are associated with painful events, results in defensive behavior and the inhibition of pain and pain-related behaviors. On the other hand, pain, produced by injurious stimulation, motivates recuperative behaviors that promote healing. In this model injurious stimulation, on the one hand, and the expectation of injurious stimulation, on the other hand, activate entirely different motivational systems which serve entirely different functions. The fear motivation system activates defensive behavior, such as freezing and flight from a frightening situation, and its function is to defend the animal against natural dangers, such as predation. A further effect of fear motivation is to organize the perception of environmental events so as to facilitate the perception of danger and safety. The pain motivation system activates recuperative behaviors, including resting and body-care responses, and its function is to promote the animal's recovery from injury. Pain motivation also selectively facilitates the perception of nociceptive stimulation. Since the two kinds of motivation serve different and competitive functions, it might be expected that they would interact through some kind of mutual inhibition. Recent research is described which indicates that this is the case. The most important connection is the inhibition of pain by fear; fear has the top priority. This inhibition appears to be mediated by an endogenous analgesic mechanism involving the endorphins. The model assumes that fear triggers the endorphin mechanism, thereby inhibiting pain motivation and recuperative behaviors that might compete with effective defensive behavior.
