A microhistory of pain

The distinction between "mental pain" and "physical pain," our legacy from Descartes, has led to a punishing skepticism about "real" pain versus "invented" pain. The specificity theory describes pain as an event in the periphery of the body that is open to interpretation, and distortion, by the mind; pain that couldn't be connected to an injury or some sort of organic cause was "psychological" and therefore suspect. This theory doesn't account for why one person can be more sensitive to pain than another, and it led to the belief that the intensity of pain is always in direct proportion to the intensity of the stimulus. But the lightest breath of air on the skin can cause severe pain for someone suffering the neuropathic pain known as reflex sympathetic dystrophy (RSD). Long after recovery from an injury, people with RSD can suffer chronic pain, to the exasperation of their doctors. The specificity theory made it possible to blame people for their own pain. Descartes could be called the father of malingering.

We now know that even the pain of a minor accident can sensitize the central nervous system in some people, as if the "on" switch for pain works, but the "off" switch is broken. People with phantom limb pain can suffer vivid, detailed pain in a hand or leg that no longer exists. Descartes was right about the fact that nerves in the periphery of the body carry signals to the brain, but not in the one-way uphill street he imagined. What science has discovered since then is that the spinal cord and central nervous system play major roles in pain perception. Descending messages from the brain can block or modify the sensory information coming in. As pain researchers Ron Melzack and Patrick Wall would demonstrate, pain is the result of a complex feedback loop.

Above all, pain is in the brain-not Descartes's passive, traffic-cop model, but one in which pain lights up multiple areas at once, a fluid, dynamic event responding to information from the senses at the same time that it shapes that response. Pain really is all in the head. But the brain doesn't just react to the foot in the flame. The body and the mind create a neural narrative together.

As neuroscience maps the brain in more detail, the gap between mind and body begins to narrow and to show itself for what it is-a false construct. The body begins to look much smarter and more soulful (flesh as "spirit thickened" as surgeon and author Richard Selzer has written) at the same time that the mind incarnates itself, as a biochemical event. Descartes's "bell" now includes not just skin, nerves, and sensation, but also memory, thoughts, and feelings.

In the nineteenth century, Silas Weir Mitchell, the father of neurology, collected case studies of nerve injuries in soldiers with gunshot wounds. His description of the mysterious burning pain of "causalgia" was part of the gradual shift away from this equation of injury to pain. What Mitchell described was a very real agony that had no obvious connection to tissue damage at all. Mitchell (to whom I will return later) also had some curious notions about women, hysteria, and pain, but he was an outstanding example of a departed nineteenth-century figure-a doctor who published both fiction and poetry, who worked both in the Weld and in the lab. Mitchell understood the relationship between pain and personal history and environment fifty years before the rest of science.

In the middle of the nineteenth century, the invention of anesthesia brought a measure of control over pain and enabled surgeons to do more complicated, lifesaving operations. We began to live longer as a result. Before anesthesia, surgery was a horrific cut-and-grab procedure that was performed as fast as possible by barbers. Anesthesiologists have been in the forefront of pain studies ever since. (The International Association for the Study of Pain, an organization of professionals in the pain Weld, was founded in 1973 by an anesthetist, John Bonica.) But the arrival of anesthesia also put the focus on erasing pain rather than exploring its role in health and disease. Anesthesiology doesn't target pain; it puts the patient in a twilight state-a kind of mock death, actually, with machines taking over the patient's vital functions. This demonstrates one of the most obvious qualities of pain: It requires a consciousness to feel it. What the unconscious patient feels as the knife cuts into him is unknown, but it's not what we call pain.

The idea of being "put to sleep" was greeted with some suspicion at first. Despite the fact that Queen Victoria gave birth to two of her children under the painkilling influence of ether, there was a cadre of obstetricians who violently opposed its use in labor. Pain was considered a necessary and natural part of giving birth, not to mention part of Eve's punishment for disobeying God.

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Excerpted from Pain: The Fifth Vital Sign by Marni Jackson. Copyright 2002 by Marni Jackson. Excerpted by permission of Random House of Canada, a division of Random House, Inc. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.