Consider the curious but tragic pain disorder called complex regional pain syndrome (CRPS). If you suffer a fracture after your finger is jammed in a doorway, pain ensues. Chronic pain results in a reflex immobilization of the hand to prevent further injury and promote healing. In a few days or weeks the tissue swelling and inflammation subside, along with the pain. But in a small percentage of cases, the immobilization turns into permanent paralysis, and the hand becomes progressively more swollen, painful, inflamed and dysfunctional. The pain and paralysis spread upward to involve the entire arm. There is no known treatment.
In a lecture we gave in 1996 at the University of California, San Diego, Decade of the Brain Symposium, we referred to this phenomenon as learned pain. Every time the motor command centers sent a command to move the hand, excruciating pain accompanying the command blocked further movement. In a few unlucky individuals, an unconscious association—or memory link—is established between the initial command itself and pain, so the brain just gives up: learned pain. Speaking metaphorically, the hand becomes immobilized by fear; it is paralyzed. Admittedly, a hand-wave argument, but nonetheless it is about as compelling an example of mind-body interactions that you can find in all of clinical medicine.
More than 20 treatments, many of them involving drugs or surgery, have been tried for CRPS. What they all have in common is they do not work. (One technique, sympathetic ganglion block, works to some extent but involves an invasive procedure.)
Can the pain be “unlearned”? Prompted by our successful pain-relief treatment using mirrors for patients with phantom limbs, Candy McCabe, now at the University of the West of England, Bristol, and her colleagues tried mirror therapy. The patient looks at the reflection and moves both hands symmetrically so that it appears to the brain that the affected arm—the left, for example—is moving but not painful after all. Similarly, stroking or hitting the right hand creates the optical illusion that the dystrophic hand is being stroked and hit with impunity. Perhaps these two bits of evidence remove the “block” on the affected arm leading to a positive cycle of pain reduction, accompanied by a reduction of swelling and redness.
Taken collectively, these were the first demonstrations that “real” chronic pain can be reduced by visual input; indeed, even intense visual imagery may turn out to be partially effective, but this is hard to do. We first tried mirror therapy on patients with phantom pain from amputated limbs. Sometimes the missing hand feels “locked” in a painfully awkward cramp that can be excruciating, and the patient cannot volitionally move the phantom. When he looks at the reflection, a series of things may happen. First, he “sees” his phantom and recognizes that it is not being poked or held in a vice after all; there is no reason for it to be painful. Second, merely seeing the phantom may be beneficial because the brain can attribute the pain to the arm and, paradoxically, a pain whose source is known may be less troubling than “disembodied,” inexplicable pain (caused by discordant visual and proprioceptive signals). Third, seeing the cramped, paralyzed hand move seems to animate it in such a way as to relieve the cramp, an example of successful clinical application of visual capture. Repeated use may lead to an unlearning of learned paralysis. In placebo-controlled clinical trials on returning war veterans, mirror visualization feedback has since been found to be strikingly successful in some patients and moderately so in others. (Jack Tsao and his colleagues at Walter Reed Army Medical Center conducted the trials.)
Remarkably, in controlled clinical trials, we and others have found mirror therapy to relieve paralysis from cerebrovascular stroke. This relief may be partly because the paralysis could be learned and partly because many paralyzed limbs also have a form of CRPS associated with them. Both these effects contribute to the limb paralysis, which would explain the relief provided by the mirrors.