Central Pain Mechanisms

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Abstract
Melzack who, with Wall,1introduced the "gate control" concept of pain some dozen years ago now has added important new insights toward a better understanding of chronic pain mechanisms. Together with Loeser,2he develops a hypothesis that explains puzzling observations about phantom body pain below the level of transection in paraplegic persons. Clearly, when all neural traffic between a body area and the brain is interrupted mechanically, impulse conduction along classic spinal pain tracts is halted. Yet, from 5% to 10% of paraplegics suffer severe discomfort from phantom body pain. Even more baffling, phantom body pain is experienced following cordectomy—the complete removal of one or more spinal cord segments. These are observations for which the segmental dorsal horn gate-control system theory provides less than satisfactory answers.3 The severity of pain in paraplegic patients often leads to several attempts at deafferentation of the phantom body site with methods