Emotional factors and individual differences in placebo analgesia. Psychophysiological experiments.

The relationship between the pain stimulus (wounds, lesions, external stimuli) and experienced pain can be modified by the context in which pain occurs: Some patients can have intolerable pain but without any physiological sign of damage. On the other han d, severe wounds may not cause pain under certain conditions, e.g. under high stress. Pain seems to be modulated by the context in which it is experienced. One especially intriguing form of pain modulation is placebo analgesia, the reduction of pain after information that a painkiller has been administrated, even if placebo is administrated. This is thought to be due to expectations that pain will be reduced. It is unclear, however, how a cognitive process like expectancy can mediate reduced pain. We prop ose that expectancies mediate reduced pain via affective mechanisms: Expectancies of reduced pain should reduce stress, which is associated with reduced pain. Four experiments that test this hypothesis is presented: Participants are chronic pain patients and healthy volunteers. Pain is either clinical or experimentally induced by thermal stimulation. Emotions are induced experimentally by use of emotional pictures and video. Pain and subjective stress are registered by visual analogue scales and questionn aires. Physiological indices of stress and emotions are startle reflex modification, skin conductance, cortisol, catecholamines, and beta-endorphin levels.