The passage discusses phantom limb phenomenon, where amputees experience sensations from limbs that are no longer physically present. It describes how phantom limbs were first documented and theorized to occur due to the brain's mental image of the body. Around 90% of amputees experience phantom limbs, which can cause severe, debilitating pain. Researchers have tried treatments like mirrors and virtual reality to provide relief, but a permanent solution has not been found. The phenomenon demonstrates that the brain believes the limb is still there based on its neurosignature or blueprint of the body created from birth.