When people lose a hand, the part of the brain dedicated to that area receives no input at all. It becomes inactive. But 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.