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But how does something like massage actually reduce pain? Why does acupuncture pacify some people and not others? And what can we do about central pain, the name for the kind of torment that Goodman and many amputees suffer every day: pain that has no localized cause, no lesion to suture or sprain to wrap? Other central-pain sufferers include those with fibromyalgia and complex regional pain syndrome, an excruciating yet mysterious pain that persists long after the original injury heals. What's exciting about CAM therapies is that they offer solutions for even these intractable and puzzling kinds of agony. In pain treatment, the only way forward may be to look back.
The Healing Power of Touch
On Nov. 1, 1985, a 56-year-old woman who had lived in the English countryside around Oxford for most of her life arrived in distress at the Radcliffe Infirmary, the hospital that first began treating Oxford's ill in the 1700s. The woman, known as Mrs. Headley, had suffered a terrible stroke. When physicians looked at a scan of her brain, they found that its right hemisphere had infarcts, areas of tissue that was dead because of a failure of blood supply.
Because the brain's right hemisphere controls the left side of the body, Headley couldn't move her left arm or hand. She was transferred to Rivermead Rehabilitation Centre, but its staff could do little for her. And yet an experimental psychologist from Oxford University, Lawrence Weiskrantz, took an interest in her case.
Most of the time, stroke patients are given a simple stimulation test to measure how much feeling remains. A little fibrous device called von Frey hairs is applied to the skin; Headley, like most severe-stroke patients, didn't feel the von Frey hairs on her left side at any level of intensity.
But then, during a break between tests, Weiskrantz noticed that Headley was rubbing her insensate hand with her normal right hand. When asked why, she quietly — but insistently — said that even though no other object produced sensation in her left hand, she could feel her right hand when it touched the left. The doctors tested her by pretending her right hand was touching the left when it wasn't. Throughout the testing, Headley knew more often than not when her right hand was returning sensation to her left.
The 1987 paper that Weiskrantz and his colleague Daren Zhang wrote about Headley has become a seminal document in the emerging science of nondrug healing. This science can be said to begin with a simple question: What's the first thing you do when you burn your hand on the stove? Put it under a faucet? Reach for ice? Actually, the first thing most people do is reflexively grasp the hurt hand with the other one. Scientists have known since at least the '60s that this kind of self-touch reduces pain. If you try to keep your other hand away, you will hurt a lot more.
Last year, researchers in three countries demonstrated in a Current Biology paper that simple touch can minimize complex central pain. They used a method called the thermal-grill illusion to prove their point.
The thermal-grill illusion was a quirky choice because it is best known as a 19th century carnival act. Subjects are asked to touch a very warm object — say, a heated but not scorching grill — and then, right afterward, a cool or room-temperature grill. Quite reliably, the participants' brains fool them into believing the second object is excruciatingly hot, even though nothing has happened to their flesh. Today we know that burning sensation as central pain.
The Current Biology team replicated the illusion in a lab experiment using water. Study participants immersed their index and ring fingers in 109°F (39°C) water and their middle fingers in 57°F (14°C) water. As in the original illusion, their middle fingers felt significantly hotter than they really were. The scientists then had participants repeat the experiment with their right fingers only. Immediately after, the subjects used the same three fingers on their left hand to touch the wet fingers on the right hand. This mere touch caused a 64% reduction in self-reported pain scores on a scale of 1 to 100.
Touch is at the core of many CAM therapies, but scientists aren't sure exactly how it works. One theory is that the healing power of touch is an evolutionary response: our ancestors had few remedies for a cut hand other than grasping it until their fellow hunter-gatherers could fashion a poultice from mud or yak dung. This evolutionary impulse may have encoded a placebo response in later generations: we came to expect that touch would reduce pain, and so we report less pain. It's also possible that evolution encoded an actual decrease in pain signals — either the number of signals or their intensity (or both) — when touch is applied to a wound.