The Changing Science of Pain

That's not to say pain is all bad. It's unpleasant, of course, but in an evolutionary sense, it has its uses. Acute pain begins in the peripheries of the body, where sensory neurons are constantly on patrol for signs of damage. They are the mechanisms that alert us to one injury so we can avoid a second one. Touch a hot stove for the first time and you won't be happy, but you'll ultimately be better off—because you'll certainly never want to do it again.

By the time it has become a chronic condition, however, pain is no longer useful. It is, as Rowe says, a disease—specifically, an overactivity of the nervous system. The brain keeps a diary of the injuries the body receives, writing each entry by reconfiguring certain neurons into new, interconnected patterns. In healthy people, these neurons stop firing once the initial damage is fixed. But in chronic pain, they keep going long after the injury has healed. "The circuits get turned up, and they stay up. They get stuck," says Gallagher. "Most diseases are physiology gone wrong. Pain is one of them."

Scientists don't know why some people develop chronic problems after injuries while others continue on with no pain. It is nearly impossible to answer the question on a wide scale; pain simply has too many causes. Some patients fully recover from massive trauma. Others, like most of the boomers with aching backs and knees, find themselves debilitated by nothing more than the accumulated, mundane strains put on joints, bones and muscles every day. Even soldiers can fall into this second category—if the bullets don't get them, the back pain brought on by months of jumping out of trucks, burdened with heavy equipment, well may.

Complicating the issue even further is pain's inherently subjective nature—we may say we "feel each other's pain," but really, we can't. Doctors don't have any good way of measuring pain from one person to the next. The best they can do is ask patients to rate it for themselves on a scale of 1 to 10, with 10 being the greatest agony of their lives. This is absurdly imprecise. Patients are usually honest (and fakery is fairly easy to spot), but they can exaggerate. A person feeling a 4 may claim a 7 to get aggressive treatment, and a person feeling a 7 may downplay it as a 4 in hopes of looking tough. Robyn Walker, a psychologist at the Tampa (Fla.) VA, says she's seen the latter dynamic in her clinic. "These patients know what a 10 feels like," she says. "But they are active-duty soldiers, and they minimize their problems. Unless you really ask them about their pain, they may be very hesitant to tell you." Doctors are trying to develop new methods of measuring pain, but their most advanced idea so far is to study facial expressions—which aren't much more standardized than the 10-point scale.

On top of that, one patient's 7 may be another's 4. "Our bodies are not one-size-fits-all," notes Rowe, "and doctors are finding that this is far more true with pain than they ever imagined." Genes may vastly influence how intensely people feel pain and how much they can withstand—although genetic testing for pain susceptibility is probably decades away. Gender matters, too. Women have up to twice as many nerve fibers in the skin as men do, so they feel some types of pain more intensely. (This doesn't mean they're weaker; it means that, all other factors being equal, their 10 is off a man's chart.) Even traits that seem unrelated to pain, like vitamin D deficiency, may increase it for reasons no one fully understands. Trying to untangle all these factors is a scientific nightmare.

Regardless of their injuries, their genes, their gender or their background, though, nearly all chronic-pain patients agree on one thing: the hyperactive neurons can make life near unbearable. The cascade of changes in the nervous system can lead to an equally painful cascade of events in a patient's life: memory loss, job loss, marital strife, depression, suicide. And through it all the body hurts like hell. "Imagine somebody holding a knife in your back and twisting it against your nerves continually, never stopping. That's what chronic pain is," says Dan O'Neal, a contractor who herniated two vertebrae in 2003 while cleaning up a job site. "At first you just shut off totally. It's terrible living like that."