10 August 2012 by Helen Thomson

A woman born missing a finger and a thumb has grown them back – albeit as part of a phantom limb. This extraordinary occurrence shows that our brain contains a fully functional map of our body image, regardless of what our limbs actually look like.

The woman, RN, was born with just three fingers on her right hand. Aged 18, RN had the hand amputated after a car accident. She later began to feel that her missing limb was still present, and developed a “phantom” hand.

"But here’s the interesting thing," says Paul McGeoch at the University of California, San Diego. "Her phantom hand didn’t have three digits, it had five."

RN was aware of a full complement of fingers, but her phantom thumb and index finger were less than half the usual length.

With training using a mirror box trick – a tool that creates the visual illusion of two hands – McGeoch and V.S Ramachandran, also at San Diego, managed to extend her short phantom finger and thumb to normal length.

McGeoch says this study indicates that there is a hardwired representation in the brain of what the body should look like, regardless of how it actually appears in real life. It shows us more about the balance between the external and innate representations of a limb, he says.

"The presence of the deformed hand was suppressing the brain’s innate representation of her fingers which is why they appeared shorter, but after the hand was removed and the inhibition taken away, the innate representation kicks in again."

Matthew Longo at Birkbeck, University of London, says it is a fascinating case study. “It contributes to a growing literature suggesting that our conscious experience of our body is, at least in part, dependent on the intrinsic organisation of the brain, rather than a result of experience.”

Source: NewScientist