The Brain and Phantom Eyelids

http://www.csiro.au/helix/sciencemail/activities/PhantomEyelids.html

The Brain and Phantom Eyelids are without looking at them. Your brain has a detailed map of your body based on what it can sense. ‘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 large clue telling your brain that your eyelids are closed is that it is dark. This a similar sense of ‘phantom eyelids’. 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 You will need because one eye is open and the other is closed.

 Yourself If you repeated the activity and covered the other eye with your hand, your brain  A space that is almost dark (such as a closet) took clues from your hand being over your face and no longer thought it was dark because the eye was shut. What to do Applications 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 Phantom limbs involve similar processes. Occasionally following an amputation, through the space under the door. 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. Wait about five minutes until your eyes are fully adjusted to the darkness. You Procedures and therapies in the past have had varying success in should be able to just barely make out some objects near you. treating this condition. 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 The areas in your brain receiving clues about where your body parts are form a off the light. 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 Move your hand away and open your eye. How does it feel? the face.

Repeat the experiment, only this time when you close the door and turn off the Removing a limb means this area of the brain is no longer receiving information. light, swap your hand to the eye that was adjusted to the light. 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 How does that feel compared with the previous time? in some confusion. Sensations from the face, for instance, might be mistakenly associated with sensations from a missing arm.

What’s happening? 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 In the first part of the experiment, most people experience a strange sensation of advantages. 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