The Tell-Tale Brain: A Neuroscientist's Quest for What Makes Us Human

Now let’s look at what this mirror-box setup does for a person with a paralyzed phantom limb. The first patient we tried this on, Jimmie, had an intact right arm, phantom left arm. His phantom jutted like a mannequin’s resin-cast forearm out of his stump. Far worse, it was also subject to painful cramping that his doctors could do nothing about. I showed him the mirror box and explained to him this might seem like a slightly off-the-wall thing we were about to try, with no guarantee that it would have any effect, but he was cheerfully willing to give it a try. He held out his paralyzed phantom on the left side of the mirror, looked into the right side of the box and carefully positioned his right hand so that its image was congruent with (superimposed on) the felt position of the phantom. This immediately gave him the startling visual impression that the phantom had been resurrected. I then asked him to perform mirror-symmetric movements of both arms and hands while he continued looking into the mirror. He cried out, “It’s like it’s plugged back in!” Now he not only had a vivid impression that the phantom was obeying his commands, but to his amazement, it began to relieve his painful phantom spasms for the first time in years. It was as though the mirror visual feedback (MVF) had allowed his brain to “unlearn” the learned paralysis.

Even more remarkably, when one of our patients, Ron, took the mirror box home and played around with it for three weeks in his spare time, his phantom limb vanished completely, along with the pain. All of us were shocked. A simple mirror box had exorcised a phantom. How? No one has proven the mechanism yet, but here is how I suspect it works. When faced with such a welter of conflicting sensory inputs—no joint or muscle feedback, impotent copies of motor-command signals, and now discrepant visual feedback thrown in via the mirror box—the brain just gives up and says, in effect, “To hell with it; there is no arm.” The brain resorts to denial. I often tell my medical colleagues that this is the first case in the history of medicine of a successful amputation of a phantom limb. When I first observed this disappearance of the phantom using MVF, I myself didn’t quite believe it. The notion that you could amputate a phantom with a mirror seemed outlandish, but it has now been replicated by other groups of researchers, especially Herta Flor, a neuroscientist at the University of Heidelberg. The reduction of phantom pain has also been confirmed by Jack Tsao’s group at the at the Walter Reed Army Medical Center in Maryland. They conducted a placebo-controlled clinical study on 24 patients (including 16 placebo controls). The phantom pain vanished after just three weeks in the 8 patients using the mirror, whereas none of the control patients (who used Plexiglas and visual imagery instead of mirrors) showed any improvement. Moreover, when the control patients were switched over to the mirror, they showed the same substantial pain reduction as the original experimental group.

More important, MVF is now being used for accelerating recovery from paralysis following stroke. My postdoctoral colleague Eric Altschuler and I first reported this in The Lancet in 1998, but our sample size was small—just 9 patients. A German group led by Christian Dohle has recently tried the technique on 50 stroke patients in a triple-blind controlled study, and shown that a majority of them regained both sensory and motor functions. Given that one in six people will suffer from a stroke, this is an important discovery.

More clinical applications for MVF continue to emerge. One pertains to a curious pain disorder with an equally curious name—complex regional pain syndrome–Type II (CRPS-II)—which is simply a verbal smoke screen for “Sounds awful! I have no idea what it is.” Whatever you call it, this affliction is actually quite common: It manifests in about 10 percent of stroke victims. The better-known variant of the disorder occurs after a minor injury such as an ordinarily innocuous hairline fracture in one of the metacarpals (hand bones). There is initially pain, of course, as one would expect to accompany a broken hand. Ordinarily the pain gradually goes away as the bone heals. But in an unfortunate subset of patients this doesn’t happen. They end up with chronic, excruciating pain that is unrelenting and persists indefinitely long after the original wound has healed. There is no cure—or at least, that’s what I had been taught in medical school.