Mind & Body

Phantom Limb Sensations Are Way More Common Than You Think

Losing a limb is a frightening idea for most. But whether it's due to disease, injury, or just being born without one in the first place, sometimes it's inevitable. Life without an arm or leg isn't just a hard thing to think about; it's hard for the motor areas of the brain to deal with. That's why some amputees experience what's known as a "phantom limb" — the feeling that their limb is still there, even when it's not. Here's why it happens, and how it's teaching scientists more about how the brain operates.

Memories of Movement

Phantom limbs sound almost made up, but they're incredibly common. If someone goes through an amputation, it's almost guaranteed that they'll experience the sensation at some point. Ninety to 98 percent of people experience a vivid phantom immediately after amputation, sometimes feeling like the limb is not only still there, but experiencing intense pain or cramping. For example, some people who lose an upper extremity feel as though their nails are digging into their palms, and others feel as if their limb is contorted in an uncomfortable position.

For many people, the phantom limb disappears within a few weeks, but for some, it hangs around for years — sometimes decades. Researcher have written about one man whose phantom accompanied him for 57 years. And limbs aren't the only thing that can appear as a phantom: Patients have reported phantom sensations from other body parts and even internal organs that have been removed, too.

There are a few things that make phantom limbs more or less likely to appear, which give scientists hints about how they work in the brain. Children are less likely to experience a phantom than adults, and the youngest children experience them the least. Since a child's brain is still developing, that suggests that phantoms must have something to do with the brain's inability to redraw its body map when it's older and less malleable.

How much the patient thought about the limb when it was intact seems to have something to do with it too. For example, you're more likely to experience a phantom if the limb caused constant pain than you are if you didn't notice the limb much day to day. Same goes for whether the amputation happened in an accident or via a planned surgery; the former is more likely to result in a phantom than the latter. That suggests that the more energy a patient's brain expends on the limb when it was intact, and the less mentally prepared they are to lose it, the more likely they are to experience it as a phantom.

Related Video: New Device Uses Phantom Limb Sensations to Control a Computer

How the Brain Responds

The area of the brain that corresponds to touch and sensation is called the somatosensory cortex, which is a region of the brain's wrinkly outer layer. Scientists have discovered that this area is an almost literal map of the body, where individual regions correspond to individual body parts: the lips are next to the face, which is next to the thumb, then the hand, et cetera. When a body part disappears, the brain gradually starts to redraw this map by giving more real estate to the neighboring features: for instance, hand neurons might be slowly taken over by face neurons. But that's not to say a person with a missing hand just has a more sensitive face — it's stranger than that. Studies of amputees have found that some will feel sensations on their face as occurring both there and in their phantom hand. It would be even stranger for someone with a lower limb amputation: In the somatosensory cortex, the closest body part to the feet is the genitals.

Theories about phantom pain, meanwhile, uncover hints about how motor commands work in the brain. When you move a limb, your brain creates two copies of the command: one to tell the limb what to do, the other to double-check after the limb sends back the "movement accomplished!" message to make sure everything went to plan. It's possible that people who experience cramping or uncomfortable positions in their phantom limb do so because the brain isn't receiving that feedback message, so it's trying harder and harder to create that movement. That's why treatments using mirrors and virtual reality seem to hold promise; if you can convince your brain that the limb is there and moving, maybe you can keep its motor commands from going haywire. Researchers still aren't sure how effective these treatments are, however.

The brain is a remarkably adaptable organ, and scientists are gradually learning how to help it adapt to life without a limb. But in the end, every new discovery about phantom limbs tells us more about the brain as a whole.

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Accidents and illness can uncover amazing things about the brain. Learn more about them in "The Tale of the Dueling Neurosurgeons: The History of the Human Brain as Revealed by True Stories of Trauma, Madness, and Recovery" by Sam Kean. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Ashley Hamer March 12, 2019

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