Woman has developed an imaginary, but useful, third arm - Boing Boing:
After having a stroke, a 64-year-old woman reports that she now has a "pale, milky-white and translucent third arm" that she can use to scratch itchy parts of her body. She also says the limb can't penetrate solid objects.
It is "the first case known to doctors of a person being able to feel, see and deliberately move a limb that doesn't exist." The woman underwent an MRI and when doctors asker her to move her imaginary third limb, her brain responded as if she really had the arm. Her visual cortex activity also indicated that she saw the arm.