‘Phantom limbs’ is a strange phenomenon where your body thinks it can feel a body part that isn’t there. Try spooking yourself with this activity which explores a similar sense of ‘phantom eyelids’.
You will need
Yourself
A space that is almost dark (such as a closet)
What to do
Find yourself a darkened room that you can completely enter, and seal out most of the light. A closet is perfect, especially if there is a tiny amount of light seeping in through the space under the door.
Wait about five minutes until your eyes are fully adjusted to the darkness. You should be able to just barely make out some objects near you.
Close and cover one eye with your hand and open the door or turn on a light. Wait a minute for it to adjust to the brightness before again closing the door and turning off the light.
Move your hand away and open your eye. How does it feel?
Repeat the experiment, only this time when you close the door and turn off the light, swap your hand to the eye that was adjusted to the light.
How does that feel compared with the previous time?
What’s happening?
In the first part of the experiment, most people experience a strange sensation of feeling as if they can’t open their uncovered eye, in spite of it being wide open, while others feel they can open it a little but it seems to be drooping or partially closed. A small minority may not experience anything strange at all.
For those who can sense this peculiar illusion, their brain is experiencing something similar to the phenomenon of ‘phantom limbs’. The brain forms an understanding of where each body part is based on certain clues from other senses. This sense is called ‘proprioception’ and explains why you know where your legs are without looking at them. Your brain has a detailed map of your body based on what it can sense.
A large clue telling your brain that your eyelids are closed is that it is dark. This lack of light is sometimes a stronger clue than the actual feeling of the eye being closed. If one eye can see some light and the other eye can’t, the brain thinks it is because one eye is open and the other is closed.
If you repeated the activity and covered the other eye with your hand, your brain took clues from your hand being over your face and no longer thought it was dark because the eye was shut.
Applications
Phantom limbs involve similar processes. Occasionally following an amputation, some people can still feel the limb that was removed. The sensation can be as mild as simply feeling its weight or touch, to extreme pain in the missing part. Procedures and therapies in the past have had varying success in treating this condition.
The areas in your brain receiving clues about where your body parts are form a map called a ‘homunculus’. Most of this nerve map makes sense – the area that feels the feet is next to the one for the leg, which is next to the one for the trunk of your body, and so on. Oddly, the area for the hands and arms is next to the one for the face.
Removing a limb means this area of the brain is no longer receiving information. The brain is incredibly adaptable, and soon starts to remap itself to make use of the unused nerves. Occasionally this isn’t as efficient as one might hope, resulting in some confusion. Sensations from the face, for instance, might be mistakenly associated with sensations from a missing arm.
It’s just another demonstration of how remarkable the brain can be, and yet still capable of making mistakes. Knowing this could be one of humanity’s biggest advantages.
