Stress induced analgesia plays an adaptive role in the organization of behavioral responding.

The data on ability of stressful or noxious stimuli to suppress the perception of pain was reviewed. The focus of this review has been the attempt to demonstrate that the emergent "Stress Induced Analgesia" (SIA) plays an adaptive role in the modulation of behavioral responding by organisms during periods of threat or danger to the organism. We have reviewed the experimental paradigms that normally used in these studies which point to the fact that the variables inducing SIA need not be actually aversive or even stressful. We also reviewed the data on the mechanisms of SIA and suggested that both opioid and nonopioid mechanisms are involved in the mediation of SIA and that these mechanisms are at least semiindependent and subject to differential conditioning. Finally, we have described a series of experiments carried out in our laboratory where the induction of SIA interacted with behavioral performance in an inverted U shape function, low levels of stress facilitated responding and learning while high levels disrupted responding. We argued that taken together, the effects of SIA seem to be highly adaptive in that it allowed animals to deal with a dangerous and threatening situation in a manner which increased the organism's chance of survival.