Harvard Medicine

More... Share to Twitter Share to Facebook
The Man in the Mirror

What can phantom sensations teach us about how our brains talk to our bodies?

He was 48 when he made passing mention of an odd pain to his internist. For at least 20 years, H. said, a mild tingling had run along his left arm and down the left side of his body, and, if he tilted his neck forward at a particular angle, it became a pronounced, electrical jolt. The internist recognized this as Lhermitte’s sign, a classic symptom that can indicate multiple sclerosis, vitamin B12 deficiency, or spinal-cord compression from a tumor or a herniated disk. An MRI revealed a pea-sized mass of dilated blood vessels pressing into the spinal cord in the patient’s neck. A week later, the tumor ruptured.

iStockphoto.comHe was raking leaves when suddenly he felt an explosion of pain, H. told me when I visited him at home two years ago. Once the swelling subsided, a neurosurgeon removed the tumor. The operation was successful, but afterward H. began experiencing a constellation of strange sensations. His left hand felt cartoonishly large—at least twice its actual size. He developed a constant burning pain along an inch-wide ribbon extending from the left side of his neck down his arm. And creeping up and down along the same band was an itch that no amount of scratching would relieve.

For eleven years, the slightest pressure could trigger an excruciating flare-up—a cool breeze across the skin, the brush of a shirtsleeve. “Sometimes I feel that my skin has been flayed and my flesh is exposed,” H. said. “Sometimes I feel that there’s an ice pick or a wasp sting. Sometimes I feel that I’ve been splattered with hot cooking oil.”

For all that, the itch was harder to endure. H. developed calluses from the incessant scratching. He tried all sorts of treatments—medications, acupuncture, herbal remedies, lidocaine injections, electrical-stimulation therapy. But nothing worked, and the condition forced him to retire in 2001.

A new understanding of perception has emerged in the past few decades, and it has overturned centuries-long beliefs about how our brains work. We believed that the hardness of a rock, the coldness of an ice cube, the itchiness of a sweater were picked up by our nerve endings, transmitted through the spinal cord, and decoded by the brain.

Our assumption had been that the sensory data we received from our eyes, ears, nose, fingers, and so on contained all the information that we needed for perception, and that perception worked something like a radio. Yet, as scientists set about analyzing sensory signals, they found them to be radically impoverished. The information we work from is poor—a distorted, two-dimensional transmission with entire spots missing. So the mind fills in most of the picture.

The fallacy of reducing perception to reception is especially clear when it comes to phantom limbs. Doctors have often explained such sensations as a matter of inflamed or frayed nerve endings in the stump sending aberrant signals to the brain. But surgeons’ efforts to cut back on the nerve typically produce relief only briefly.

Moreover, the feelings people experience in their phantom limbs are far too varied and rich to be explained by the random firings of a bruised nerve. People report not just pain but also sensations of sweatiness, heat, texture, and movement in a missing limb. Children have used phantom fingers to count and solve arithmetic problems.

More recently, researchers have begun to believe that perception is the brain’s best guess about what is happening in the outside world. The mind integrates scattered, weak, rudimentary signals from sensory channels, information from past experiences, and hard-wired processes, and produces a perceptual experience full of brain-provided color, sound, texture, and meaning.

The theory has begun to make sense of some bewildering phenomena. Among them is an experiment that Vilayanur Ramachandran, director of the Center for Brain and Cognition at the University of California, San Diego, performed with volunteers who had phantom pain in an amputated arm. The volunteers each put the surviving arm through a hole in the side of a box with a mirror inside, so that, peering through the open top, they could see the real arm and its mirror image. Ramachandran then asked them to move both the intact arm and, in their minds, the phantom arm. The patients regained the sense that they had two arms. Even though they knew it was an illusion, the exercise provided immediate relief.

This experiment suggests that when your arm is amputated, nerve transmissions are shut off, and the brain’s best guess often seems to be that the arm is still there, but paralyzed, or clenched, or beginning to cramp. The mirror box provides the brain with new visual input—however illusory—suggesting motion in the absent arm. The brain incorporates the new information into its sensory map; it guesses again, and the pain dissipates.

The morning I visited H., he told me that he thought his problem was basically a “bad switch” in his neck where the tumor had been, a kind of loose wire sending false signals to his brain. But I told him about the increasing evidence that our sensory experiences are not sent to the brain but originate in it. When I mentioned that he might want to try the mirror-box treatment, he agreed.

He brought a cheval glass down to the living room, and I had him stand with his chest against the side of it, so that his troublesome left arm was behind it and his normal right arm was in front. He tipped his head so that when he looked into the mirror the image of his right arm seemed to occupy the same position as his left arm. Then I asked him to wave his arms as if conducting an orchestra.

At first, he expressed disappointment. “It isn’t quite like looking at my left hand,” he said. But then suddenly it was.

“Wow!” he said. “Now, this is odd.”

After a moment or two, I noticed that he had stopped moving his left arm. Yet he reported that he felt as if it were still moving. What’s more, the sensations in it had changed dramatically. For the first time in eleven years, he felt his left hand “snap” back to normal size. The burning pain diminished. And the itch was dulled.

“This is positively bizarre,” he said.

He still felt the pain and the itch in his neck and shoulder, where the image in the mirror cut off. And, when he came away from the mirror, the aberrant sensations in his left arm returned. He began using the mirror a few times a day, for fifteen minutes at a stretch. After a couple of weeks, his hand returned to feeling normal all day long.

The mirror also provided him with the first effective treatment for his flare-ups. Where once he could do nothing but wait for the torment to subside, he now just pulls out the mirror. “I’ve never had anything like this before,” he said. “It’s my magic mirror.”

Atul Gawande ’94, MPH, is a surgeon at Brigham and Women’s Hospital, an associate professor of surgery at Harvard Medical School, an associate professor in health policy and management at the Harvard School of Public Health, and a staff writer for The New Yorker. His latest book, The Checklist Manifesto: How to Get Things Right (Metropolitan Books, 2009), explores strategies for preventing medical errors. This essay was excerpted and adapted with permission from “The Itch” in the June 30, 2008, issue of The New Yorker.


Add new comment