“Pain inhibits pain,” a phenomenon whereby we perceive less pain from a noxious stimulus when a separate painful stimulus is applied to another part of the body, may seem paradoxical at first. However, this observation is firmly supported by pain science and is grounded in the complex interactions within the body’s endogenous pain modulation system. Known as conditioned pain modulation in humans, or descending control of nociception in animals, this intrinsic ability to alter pain sensitivity gives us unique insights into how endogenous pain modulation shifts the balance between pain facilitation and pain inhibition in nociceptive processing. Dysfunction of this finely tuned system is a major contributing factor in several clinically significant chronic pain conditions, such as fibromyalgia, diabetic neuropathy, migraine headache, chronic postsurgical pain, and others. Some of the most widely used pain medications are thought to act through the endogenous pain modulation system. For instance, the...

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