Authors: Oliver Sacks
P
hantom limbs are hallucinations insofar as they are perceptions of something that has no existence in the outside world, but they are not quite comparable to hallucinations of sight and sound. While losing one’s eyesight or hearing may lead to corresponding hallucinations in 10 or 20 percent of those affected, phantom limbs occur in virtually all who have had a limb amputated. And while it may be months or years before hallucinations follow blindness or deafness, phantom limbs appear immediately or within days after an amputation—and
they are felt as an integral part of one’s own body, unlike any other sort of hallucination. Finally, while visual hallucinations such as those of Charles Bonnet syndrome are varied and full of invention, a phantom closely resembles the physical limb that was amputated in size and shape. A phantom foot may have a bunion, if the real one did; a phantom arm may wear a wristwatch, if the real arm did. In this sense, a phantom is more like a memory than an invention.
The near universality of phantom limbs after amputation, the immediacy of their appearance, and their identity with the corporeal limbs in whose stead they appear suggest that, in some sense, they are already in place—revealed, so to speak, by the act of amputation. Complex visual hallucinations get their material from the visual experiences of a lifetime—one has to have seen people, faces, animals, landscapes to hallucinate them; one has to have heard pieces of music to hallucinate them. But the feeling of a limb as a sensory and motor part of oneself seems to be innate, built-in, hardwired—and this supposition is supported by the fact that people born without limbs may nonetheless have vivid phantoms in their place.
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The most fundamental difference between phantom limbs and other hallucinations is that they can be moved voluntarily, whereas visual and auditory hallucinations proceed autonomously, outside one’s control. This was also emphasized by Weir Mitchell:
[The majority of amputees] are able to will a movement, and apparently they themselves execute it more or less effectively.… The certainty with which these patients describe their [phantom motions], and their confidence as to the place assumed by the parts moved, are truly remarkable … the effect is apt to excite twitching in the stump.… In some cases the muscles which act on the hand are absent altogether; yet in these cases there is fully as clear and definite a consciousness of the movement of the fingers and of their change of positions as in cases [where the muscles of the hand are partially preserved].
Other hallucinations are only sensations or perceptions, albeit of a very special sort, whereas a phantom limb is capable of phantom
action
. Given a suitable prosthesis, the phantom limb will slip into the prosthesis (“like a hand into a glove,” as many patients say)—slip into it and animate it, so that the artificial limb can be used like a real one. Indeed, this must happen if one is to use a prosthesis effectively. The artificial limb becomes part of one’s body, of one’s body image, as a cane in a blind man’s hand becomes an extension of himself. One may say that an artificial leg, for instance, “clothes” the phantom, allows it to be effective, gives it an objective sensory and motor existence, so that it can often “feel” and respond to
minute irregularities in the ground almost as well as the original leg.
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(Thus the great climber Geoffrey Winthrop Young, who lost a leg during World War I, was able to climb the Matterhorn using a prosthetic limb of his own design.)
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One might go further and say that a phantom is a portion of body image which is lost or dissociated from its natural, embodying home (the body)—and, as such, as something extraneous, it may be intrusive or deceptive (thus the danger of walking off a curb with a phantom leg). The lost phantom (if one can speak figuratively) longs for a new home, and it will find this in a suitable prosthesis. I have had many patients tell me how they may be disturbed by their phantom at night but relieved in the morning, for the phantom disappears the moment they put on their prosthesis—disappears, that is,
into
the prosthesis, merging so seamlessly with it that phantom and prosthesis become one.
Knowledge of what one is doing with one’s phantom—even without a prosthesis—can be exquisitely refined. As a young student, Erna Otten, a distinguished pianist, was a pupil of the great Paul Wittgenstein, who lost his right arm in the First
World War but continued to play with his left hand (and commissioned a number of composers to write music for the left hand). Yet he continued to teach, in a sense, with both hands. In a letter to the
New York Review of Books
, responding to an article I had written, Otten wrote:
I had many occasions to see how involved his right stump was whenever we went over the fingering for a new composition. He told me many times that I should trust his choice of fingering because he felt every finger of his right hand. At times I had to sit very quietly while he would close his eyes and his stump would move constantly in an agitated manner. This was many years after the loss of his arm.
Unfortunately, not all phantoms are as well formed, as painless, or as mobile as Wittgenstein’s. Many show a tendency to shrink or “telescope” with time—a phantom arm may be reduced to a hand seemingly sprouting from the shoulder. This tendency to shrink is minimized by embedding the phantom in a prosthesis and using it as much as possible. A phantom may also become paralyzed or contorted in painful positions, with its “muscles” in spasm. Thus Admiral Lord Nelson, after losing his right arm in battle, developed a phantom limb with the hand permanently clenched, the fingers digging excruciatingly into the palm.
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Such disorders of body image have long seemed inexplicable and untreatable. But over the last few decades, it has become clear that the body image is not as fixed as we once thought; indeed, it is remarkably plastic, and extensive reorganization or remapping can occur with phantom limbs.
If there is interruption of nerve function from injury or disease in the spinal cord or peripheral nerves, cutting off or reducing normal sensory input to the brain, this may cause major disturbance of body image, with strange phantom images superimposed on the real but insentient body parts. This was very striking with a colleague of mine, Jeannette W., who broke her neck in a car accident and became quadriplegic, with a complete absence of sensation below the level of the fracture. She had, in a sense, been “amputated” from the neck down and had little sense of her body below this. But in its place, she had a phantom body, which was unstable and prone to distortions and deformations. She could reverse these, for a while, by
seeing
that her body still had a normal shape and conformation, and she arranged for mirrors to be set up in her office and in the hospital corridors, so that she could glance up and (in her words) take “visual sips” from them as she bowled past in her wheelchair.
As normal sensation is blocked, body image disturbances can occur very quickly. Most of us have had strange phantom experiences with dental anesthesia, of a grotesquely swollen, deformed, or misplaced cheek or tongue. Looking in a mirror will do little to dispel these illusions, which disappear only with the return of normal sensation. One patient of mine, with the removal of a large brain tumor, had to sacrifice the roots of the sensory nerves on one side of her face. For years following this, she had a persistent sense that the whole right side
of her face was “slipping,” “caved in,” or “missing”; that her tongue and cheek on this side were tremendously swollen and grotesque-looking. She later came to have a leg amputated, and soon after surgery became aware of a phantom leg. Now, she said, “I know what’s wrong with my face. It’s exactly the same feeling—I have a phantom face.”
There can also be extra limbs—supernumerary phantoms—if certain areas of the body are denervated. A striking example of this was described by Richard Mayeux and Frank Benson. Their patient was a young man with multiple sclerosis who developed a numbness on his right side and then experienced, as they wrote,
a tactile illusion that a second right arm was lying across his lower chest and upper abdomen. The extra arm seemed to be attached to the chest wall.… There was only a vague sensation of the duplicate illusory lower forearm, wrist, and palm, but a vivid impression of the fingers lying on the abdominal wall.… The illusion persisted for period of 5 to 30 minutes and was accompanied by a “gripping” sensation of the illusory hand.… The phantom limb sensation was always coincident with feelings of increased stiffness, numbness, and burning [sensations] of the actual right arm.
N
elson’s clenched hand exemplifies an unpleasant evolution which phantom limbs may undergo—phantoms which are initially loose, mobile, and obedient to the will may subsequently become paralyzed, contorted, and often intensely painful. Before the 1990s, there was no plausible explanation as to why phantom limbs might get frozen in
this way, nor any notion of how to unfreeze them. But in 1993, V. S. Ramachandran suggested a physiological scenario which might explain the progressive loss of voluntary movement so common in phantom limbs. The vivid sense that one could move a phantom limb freely, he thought, went with the brain being able to monitor its own motor commands to the phantom. But with the continuing absence of visual or proprioceptive confirmation of movement, the brain, in effect, might “abandon” the limb. Thus, Ramachandran thought, paralysis was “learned,” and he wondered whether it could be unlearned.
Could one, by simulating visual and proprioceptive feedback, dupe the brain into believing that the phantom was once again mobile and capable of voluntary movement? Ramachandran developed a brilliantly simple device—an oblong wooden box with its left and right sides divided by a mirror, so that looking into the box from one side or the other, one would get an illusion of seeing both hands, where in reality one was seeing only one hand and its mirror image. Ramachandran tried this device on a young man who had had a partial amputation of his left arm—his now-rigid phantom hand, Ramachandran wrote, “jutted like a mannequin’s resin-case forearm out of the stump. Far worse, it was also subject to painful cramping that his doctors could do nothing about.”
After explaining what he had in mind, Ramachandran asked the young man to “insert” his phantom arm to the left of the mirror. Ramachandran described this in his book
The Tell-Tale Brain:
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.
This extremely simple procedure (which was devised only after much careful thinking and a whole, very original theory as to the many interacting factors involved in the production of phantoms and their vicissitudes) can easily be modified for dealing with phantom legs and a variety of other conditions involving distortion of body image.
The
appearance
of the hand moving, the optical illusion, was sufficient to generate the
feeling
that it was moving. I described the converse of this in
The Mind’s Eye
, when the existence of a large blind spot in my visual field allowed me, visually, to “amputate” a hand. But if, when I had done this, I opened and closed my fist or moved my now-invisible fingers, a sort of pink protoplasmic extension grew out of my visual “stump” and developed into a (visual) phantom of the hand.
Jonathan Cole and his colleagues have made similar observations, testing a virtual reality system to reduce phantom pain. In their experiments with leg and arm amputees, the amputated stump is connected to a motion capture device, which in turn determines the movements of a virtual arm or
leg on a computer screen. Most of their subjects learned to correlate their own movements with those of the on-screen avatar, and developed a sense of agency or ownership, so that they were able to move the virtual limb with surprising delicacy (for instance, to reach for and grasp a virtual apple lying on the surface of a virtual table). Such learning occurred remarkably quickly, within half an hour or so. With this sense of agency and intentionality often came a reduction in phantom pain—and even virtual perception. One man, for example, could “feel” the virtual apple when he picked it up. Cole and his colleagues wrote, “Perception was not only of motion of the limb but also of touch, a virtual-visual cross-modal perception.”
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n 1864, Weir Mitchell and two of his colleagues put out a special circular from the Surgeon General’s Office, entitled
Reflex Paralysis
. In reflex paralysis, the injured limb is intact, but it cannot be moved; it seems absent or “alien,” not part of the body. It is, in a sense, the opposite of a phantom limb—an external limb with no internal image to give it presence and life.
I had such an experience in 1974 during the mountaineering accident in which I ruptured the quadriceps tendon in my left leg. Though the tendon was repaired surgically, there was damage at the neuromuscular junction, and additionally, the leg was hidden from sight and touch, immobilized in a long, opaque cast. Under these circumstances, where it was impossible to send commands to the injured muscle and there was no sensory or visual feedback, the leg disappeared from my body image, leaving (so it seemed to me) an inanimate, alien thing in its place. This continued to be the case for thirteen
days. (Thinking back on this experience, I wonder whether one of Ramachandran’s mirror boxes would have helped me to recover movement, and a sense of reality, in this leg sooner. It might have helped, too, had the cast been transparent, so that I could at least see the leg.)