Why do amputees feel pain in limbs that no longer exist?

The answer

Phantom limb pain affects up to 80% of amputees and arises because the brain maintains an internal 'body map' in the somatosensory and motor cortices. After amputation, the cortical regions that previously represented the missing limb do not go silent; instead, neighboring cortical areas invade the vacated territory, creating disorganized signals that the brain interprets as pain or sensation from the missing limb. V.S. Ramachandran pioneered mirror box therapy, where the patient views the reflection of their intact limb in place of the missing one, tricking the brain into 'seeing' the phantom limb move and relax, which can dramatically reduce pain. Modern treatments also include virtual reality systems and targeted muscle reinnervation surgery.