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A Moment of Science

The Reappearing Hand

A surprising phenomenon sometimes occurs to people who have lost a hand. Soon after the hand is lost, they report that they can feel it again, this time when something touches the side of their face. A neurologist can lightly touch different areas on the cheek, for example, and the person will say it feels as if two spots were being touched simultaneously. One on their face, and one on their missing hand.

Although this seems eerie, the explanation is not at all supernatural. Your brain is equipped with a map of your entire body. When you stub your toe, for example, the part of the brain’s map that represents your toe is activated, and you feel the sensation in a specific place.

When people lose a hand, the part of the brain dedicated to that area receives no input at all. It becomes inactive. However, the areas around it are still getting signals all the time. Some of those signals seem to leak over into the unused area.

Just by coincidence, the area next to the one dedicated to the hand is dedicated to the cheek. So, you can get a situation where real information coming from the cheek registers in two places at once. The place dedicated to the cheek, and the place that used to be dedicated to the hand.

This information shows us that the brain is less of a hard-and-fast kind of thing than we once thought. Its natural tendency to re-wire itself may some day allow us to help people recover from strokes or other brain-damaging injuries.

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