Woman gains "third arm" following stroke

Following a stroke, a woman in Switzerland developed an imaginary third arm that looked and felt as real to her as the arms she'd always had.

Scientists subjected her to tests, and discovered that the phantom limb is indeed just as real as her other limbs, as far her brain's perception of it is concerned. When she is asked to move the arm, her motor cortex shows the signs of moving an actual limb. When she is asked to look at her third arm, her visual cortex responds as if its watching the arm move.

At least the poor woman got one small benefit out her stroke - she's now able to scratch her itches without anybody knowing! While her imaginary third arm passes through solid objects, when she uses it to scratch her own skin, her brain perceives it as actual scratching.