Psychophysics of pain

Abstract

The experience of pain serves two primary purposes, both critical for survival. Pain is foremost a warning signal, protecting the organism from harm or at least minimizing injury. Pain receptors, or nociceptors, are widespread. An extensive network of nociceptors can signal damage from anyplace on the skin, or in deeper tissues including muscles and viscera. Nociceptors are divided into systems with sensitivities to a number of modalities such as cold, heat, pressure, and chemical stimulation. The second major function of pain occurs after injury. Intrinsic mechanisms exacerbate pain intensity, location, and duration. Pain spreads from the injured area into noninjured regions, and persists during healing. While the presence of a pain exacerbation system seems paradoxical, it is now quite clear that this system serves a recuperative role. Augmented pain causes the injured organism to be immobile and to adapt postures that may protect the injured part, behaviors (or actually the absence of behaviors) that promote natural healing mechanisms. The multiple modalities and purposes of pain lead to a wide variety of pain experience, varying in intensity, duration, locus, quality, and feeling state. Most studies of pain do not attempt to evaluate this complexity of pain, instead simplifying the richness of the experience into a single dimension of pain intensity. A group of studies double the dimensions, assessing both the sensory intensity and the unpleasantness of pain sensations, principal dimensions found in other sensory systems such as heat, cold, taste, and smell. Finally, a group of studies focus on all of the relevant dimensions of pain experience, discovering the number and type of salient dimensions, and how these vary over different syndromes, individuals, and in response to treatments. This chapter will briefly consider all three approaches, presenting the issues associated with studies that measure just pain, pain intensity, and pain unpleasantness, or every possible dimension of pain experience. © 2008 Published by null.