Feeling a Hand That Is Not There
Imagine reaching for a cup with a hand you no longer have. For many people who have had an amputation, that is a real experience. Between 50% and 80% of them go on to feel a phantom limb.
The feeling can be very strong. People may sense that the missing limb is still part of their body. They feel as if they are gesturing, feel itches, feel it twitch, or even try to pick things up with it. The missing limb often feels shorter than it was, and it may seem stuck in an odd, uncomfortable position.
Some of these feelings are painful, and some are not. Phantom limb pain comes and goes for most people, though for some it is constant. Stress, anxiety and weather changes can make it worse, especially freezing cold. The good news is that attacks usually become less frequent and less intense over time.
A Sensory Ghost Gets a Name
The term "phantom limb" was coined in 1872 by a physician named Silas Weir Mitchell. He described it, almost like a poet, as a "sensory ghost" of the missing part, sometimes faintly felt and ready to be called up by a touch or a change of wind.
He was not the first to notice it. In the 1500s, a French military surgeon named Ambroise Paré saw that some of his patients kept reporting pain in a limb he had already removed.
For many years, doctors blamed irritated nerves at the site of the amputation, a lump known as a neuroma. Then, by the late 1980s, researcher Ronald Melzack spotted a big problem with that idea. Many people born without limbs also felt phantom limbs. So the nerves at a wound could not be the whole story. Melzack suggested the feeling of having a body comes from a wide network in the brain, which he called the neuromatrix.
When Your Face Touches Your Missing Hand
In 1991, a team led by Pons at the National Institutes of Health found something striking in macaque monkeys. After a loss of feeling from part of the body, the somatosensory cortex, the brain area that handles touch, reorganized itself in a big way.
That gave scientist V. S. Ramachandran an idea. Maybe the same thing happens in people with phantom limbs. He and his team stroked different parts of amputees' faces, and the patients felt touches on different parts of their missing limb. Later brain scans of amputees showed the same kind of rewiring seen in the monkeys.
The brain holds a touch map of the body, called the sensory homunculus. Body parts with larger areas on that map, such as the hands, feet, fingers and toes, tend to produce more phantom feelings. When a nearby brain region takes over the empty space, a touch elsewhere can be read as a touch on the missing limb.
Moving, Shrinking and Tingling
Scientists sort phantom feelings into three types. Kinetic sensations are feelings of movement, like sensing your toes flex. Kinesthetic sensations are about size, shape or position, like feeling that your hand is twisted. Exteroceptive sensations are about touch, pressure, tingling, temperature, itching and vibration.
There is also a strange effect called telescoping. The missing limb feels as if it is slowly getting shorter and pulling in closer to the body.
Phantom feelings are not only about arms and legs. They can also show up after the removal of a tooth, known as phantom tooth pain, or of an eye, known as phantom eye syndrome. Phantom limb pain is usually grouped with neuropathic pain, meaning pain that comes from the nerves themselves. Even after a great deal of research, there is still no clear agreement on exactly what causes it. Both the brain and the nerves in the rest of the body may play a part.
Mirrors and Virtual Arms
Many treatments have been tried, from medicines to spinal cord stimulation, vibration therapy, hypnosis and virtual reality. Most traditional treatments are not very effective, and good evidence that one beats another is lacking.
One simple idea caught public attention: the mirror box. Ramachandran introduced mirror therapy in the early 1990s. A mirror shows a reflection of the healthy hand where the missing one would be. That lets the patient "move" the phantom and unclench it from painful positions. A 2018 review found 15 good-quality studies out of 115 publications and called it a valid, simple and inexpensive treatment. The debate is still open, though.
Virtual reality takes the trick further. Patients see a virtual limb that responds in real time to movements picked up by sensors. In one trial with 81 people across 9 clinics in seven countries, phantom pain dropped by 64.5% in one group and 68.2% in another.
