John Register turned out to be wrong: The amputation didn't get rid of the pain. It did allow him to return to track and field, though; he long-jumped nearly 18½ feet to win the silver medal at the 2000 Paralympics in Sydney. But after the surgery he continued to feel an ankle and foot beyond his stump—at times he would sense a knife being dragged across his nonexistent Achilles tendon. In time the sensations faded, but he still has nights when he feels an electric shock in his phantom foot, and he crawls out of bed so that his twitching doesn't wake his wife.
It is now well-known that there can be pain in the absence of injury, and horrendous injury in the absence of pain, with many shades in between. A kidney stone, for example, is biologically trivial and unthreatening and affects a part of the body with relatively few nerves, yet it causes excruciating pain. These are blows to the sanctity of Descartes's specificity theory.
In 1965, 301 years after Descartes's treatise, Melzack, the Canadian psychologist, and his colleague Patrick D. Wall, a British neuroscientist, proposed that the brain is not a passive recipient of pain information but rather an active gatherer of relevant data from the skin and organs that has ultimate say in dispensing pain as it sees fit. If the nerve fibers compose a web in the body, the brain is the spider at the center, using the web as a data-collecting extension of its body. Each vibration of the web reveals the location and size of the intruding sensation and sets other strands vibrating that the spider must collectively interpret to decide on a course of action. And just as experience in the wild teaches the spider to become an increasingly savvy decision maker, so does experience act upon the brain. Among Melzack's revelations was that part of the brain's hardware is what he called a pain "neuromatrix," essentially a blueprint of a full body that exists in the brain whether or not the full body exists in physical space. But to interpret the sensation of pain, he found, the brain has to install specific software.
In the 1950s, Melzack was working toward his Ph.D. at McGill under psychologist D.O. Hebb. At the time there was no such field as pain research—pain was considered a side effect of illness or injury. Hebb was interested in how an extreme dearth of life experience affects intelligence. His subjects were Scottish terriers. He would feed and groom them himself but isolate them from the outside world, then analyze their ability to navigate a maze. What Melzack noticed was that the experience-deprived dogs ran headlong into water pipes in the holding room over and over, with no apparent feelings of pain. The dogs, he found, also had no aversion to fire. Melzack lit a match and held it out to see how the terriers would react to something they had never seen. The dogs stuck their noses in the flame, backed up and calmly did it again. And again and again. Whatever the critical developmental period was for loading pain software into the brain, the dogs had missed it. As Mogil puts it, "The fact that something like pain would have to be learned at all is pretty surprising."
Ivan Pavlov, the most famous dog experimenter, showed that animals' pain perception could be programmed. When dogs were given an electric shock on the paw, they recoiled violently. But then Pavlov presented his dogs with food after each shock on a particular paw. Soon they ceased recoiling—instead wagging their tails and salivating at each shock. If the opposite paw was shocked, however, the dogs reacted as violently as before.
Melzack elegantly summarized all the psychological influences that modify the biological experience of pain by saying that the "meaning of the situation" has a tremendous effect, by actually altering the nerve impulses from the body to the brain and within the brain itself.
Toward the end of his 13-year NFL career, Jerome Bettis had a Monday morning ritual: He would sit at the top of his staircase, then scoot downstairs on his butt because he was simply unable to walk down. Bettis, who finished with 3,479 carries, may have taken more shots than any other straight power back in pro football history. Among his injuries were broken ribs, a torn groin muscle, a bruised sternum and two separated shoulders. Once he played with cotton stuffed inside a broken nose, but a head-on collision sent the pieces up through his nasal passage, down his throat and into his stomach. "My skill was running through people," he says. "That was all I had. It wasn't like I could run away from them."
By the following Sunday he would recover. Sometimes. The older he got, the longer it took before he was fully mobile again. In his final seasons with the Steelers, it wasn't until Thursday or Friday that he felt ready to go. In 2005, Bettis's last year, he recalls taking a helmet to the quadriceps in a Week 6 game against Jacksonville. "My quad was just on fire," he says. "I was rehabbing and doing everything I could. But on Saturday I said to myself, I can't move. I'm not going to be able to play." Come Sunday, though, he was on the field.
The power of game day to suppress pain should not be underestimated. In 1998, Haverford College psychologist Wendy Sternberg was talking to a student about stress-induced analgesia (SIA)—the temporary absence of pain that Tim Sylvia and Beecher's soldiers experienced after serious injuries. SIA is not fully understood, but part of the pain relief appears to come from the body's ramped up production of endorphins and opioids, natural chemicals that reduce our perception of pain and stress. Sternberg's student told her that SIA was reminiscent of athletes competing through pain. So Sternberg put the hypothesis to the test. She tested the pain sensitivity of track athletes, basketball players and fencers at Haverford immediately after competition, compared to two days before and two after. Sure enough, on game day the athletes were less sensitive to heat or cold. For Sternberg the key implication was that athletic competition kicks in the body's pain-inhibition circuitry. Sunday makes people tougher.
And the more Sundays you play, the tougher you get. As Bettis says, "You become conditioned to the pain."