Mirror Box Treatment for Phantom Pain
V. S. Ramachandran asked a most daring question; whether phantom paralysis and pain could be "unlearned."
Ramachandran then hit on the wizard like idea of fighting one illusion with another. What if he could send false signals to the brain to make the patient think that the nonexistent limb was moving? That question led him to invent a mirror box designed to fool the patient's brain. It would show him the mirror image of his good hand in order to make him believe it was his amputated hand "resurrected."
The mirror box is the size of a large cake box, without a top, and is divided into two compartments, one on the left and one on the right. There are two holes in the front of the box. If the patient's left hand was amputated, he puts his good right hand through the hole and into the right compartment. Then he is told to imagine putting his phantom hand into the left compartment.
The divider that separates the two compartments is a vertical mirror facing the good hand. Because there is no top on the box, the patient can, by leaning a bit to the right, see a mirror image reflection of his good right hand, which will seem to be his left hand as it was before the amputation. As he moves his right hand back and forth, his "resurrected" left hand will also appear to move back and forth, superimposed on his phantom.
The mirror box appears to cure pain by altering the patients' perception of their body image. This is a remarkable discovery because it sheds light both on how our minds work and on how we experience pain.
Pain and body image are closely related. We always experience pain as projected into the body. When you throw your back out, you say, "My back is killing me!" and not, "My pain system is killing me." But as phantoms show, we don't need a body part or even pain receptors to feel pain. We need only a body image, produced by our brain maps. People with actual limbs don't usually realize this, because the body images of our limbs are perfectly projected onto our actual limbs, making it impossible to distinguish our body image from our body. "Your own body is a phantom," says Ramachandran, "one that your brain has constructed purely for convenience."
Distorted body images are common and demonstrate that there is a difference between the body image and the body itself. Anorexics experience their bodies as fat when they are on the edge of starvation; people with distorted body images, a condition called "body dysmorphic disorder," can experience a part of the body that is perfectly within the norm as defective. They think their ears, nose, lips, breasts, penis, vagina, or thighs are too large or too small, or just "wrong," and they feel tremendous shame. Marilyn Monroe experienced herself as having many bodily defects. Such people often seek plastic surgery but still feel misshapen after their operations. What they need instead is "neuroplastic surgery" to change their body image.
According to Ramachandran, pain, like the body image, is created by the brain and projected onto the body. This assertion is contrary to common sense and the traditional neurological view of pain that says that when we are hurt, our pain receptors send a one-way signal to the brain's pain center and that the intensity of pain perceived is proportional to the seriousness of the injury.
Ramachandran developed his next idea: that pain is a complex system under the plastic brain's control. He has also said that "pain is an illusion" and that "our mind is a virtual reality machine," which experiences the world indirectly and processes it at one remove, constructing a model in our head. So, pain, like the body image, is a construct of our brain.
Since Ramachandran could use his mirror box to modify a body image and eliminate a phantom and its pain, could he also use the mirror box to make chronic pain in a real limb disappear?
Ramachandran thought he might be able to remedy "type 1 chronic pain," experienced in a disorder called "reflex sympathetic dystrophy." This occurs when a minor injury, a bruise, or an insect bite on the fingertip makes an entire limb so excruciatingly painful that "guarding" prevents the patient from moving it. The condition can last long after the original injury and often becomes chronic, accompanied by burning discomfort and agonizing pain in response to a light brushing or stroking of the skin.
Ramachandran theorized that the brain's plastic ability to rewire itself was leading to a pathological form of guarding. When we guard, we prevent our muscles from moving and aggravating our injury. If we had to remind ourselves consciously not to move, we'd become exhausted and slip up, hurt ourselves, and feel pain. Now suppose, thought Ramachandran, the brain preempts the mistaken movement by triggering pain the moment before the movement takes place, between the time when the motor center issues the command to move and the time when the move is performed. What better way for the brain to prevent movement than to make sure the motor command itself triggers pain? Ramachandran came to believe that in these chronic pain patients the motor command got wired into the pain system, so that even though the limb had healed, when the brain sent out a motor command to move the arm, it still triggered pain.
Ramachandran called this "learned pain" and wondered whether the mirror box could help relieve it.
Why? One thought was that these long-term patients had not moved their guarded limbs for so long that the motor maps for the affected limb had begun to waste away — once again use it or lose it.
An Australian scientist, G. L. Moseley, thought he might be able to help the patients who hadn't improved by using the mirror box, often because their pain was so great they couldn't move their limbs in mirror therapy. Moseley thought that building up the affected limb's motor map with mental exercises might trigger plastic change. He asked these patients to simply imagine moving their painful limbs, without executing the movements, in order to activate brain networks for movement. The patients also looked at pictures of hands, to determine whether they were the left or right, until they could identify them quickly and accurately — a task known to activate the motor cortex. They were shown hands in various positions and asked to imagine them for fifteen minutes, three times a day. After practicing the visualization exercises, they did the mirror therapy, and with twelve weeks of therapy, pain had diminished in some and had disappeared in half.
Think how remarkable this is — for a most excruciating, chronic pain, a whole new treatment that uses imagination and illusion to restructure brain maps plastically without medication, needles, or electricity.
Ramachandran and Eric Altschuler have shown that the mirror box is effective on other non-phantom problems, such as the paralyzed legs of stroke patients. Mirror therapy differs from Taub's in that it fools the patient's brain into thinking he is moving the affected limb, and so it begins to stimulate that limb's motor programs. Another study showed that mirror therapy was helpful in preparing a severely paralyzed stroke patient, who had no use of one side of the body, for a Taub-like treatment. The patient recovered some use of his arm, the first occasion in which two novel plasticity-based approaches — mirror therapy and CI-like therapy — were used in sequence.
Excerpted from the book: The Brain That Changes Itself
Stories of Personal Triumph from the Frontiers of Brain Science
By Norman Doidge, MD, Penguin Publishing, December, 2007