Pain Signal as Threat and Reward

It has long been recognized, albeit not always broadly appreciated, that pain constitutes a complex physiological experience with variable significance and meaning across individuals and contexts. When describing the bodily expressions to emotional and physical pain, Charles Darwin, in his Expression of the Emotions (1872), noted, ‘‘After the mind has suffered from an acute paroxysm of grief, and the cause still continues, we may fall into a state of low spirits [.]. Prolonged bodily pain, if not amounting to an agony, generally leads to the same state of mind. If we expect to suffer, we are anxious; if we have no hope of relief, we despair.’’ The study of the neural mechanisms involved in the perception, transmission, representation, and regulation of pain has indeed uncovered a complex neural system that integrates painful information to permit the adaptation of the organism to potential bodily injury or tissue damage (Rainville et al., 2001). Perhaps as anticipated by Darwin’s observations, this socalled ‘‘pain matrix’’ shares circuitry with the processing of information related to emotional responses, the assessment of the intensity, pleasantness and unpleasantness of various sensory stimuli, and their meaning, whether reward or punishment. Collectively, these neural systems are broadly being referred to as motivational circuitry, modulating decisionmaking processes and subsequent behavior (Craig, 2002; Heekeren et al., 2008; Wittmann et al., 2008). Baliki and coauthors (2010) (this issue of Neuron) utilized functional magnetic resonance imaging to examine the brain regional responses to the expectation and receipt of brief painful stimuli of various temperatures, each lasting from 12 to 30 s, randomly presented, while