A woman born without a finger and thumb on her right hand 'grew' the missing digits back as part of a phantom limb after her hand was amputated.
The 57-year-old woman, known as RN, had her hand amputated after a car accident when she was 18.
She began to feel the sensation of her hand still being there, but with four fingers and a thumb.
Neuroscientists at the University of California, San Diego said RN's experience showed the brain has its own internal template of how the body should look.
RN's phantom index finger and thumb were not full length and became painful.
Dr Paul McGeoch and Professor V.S Ramachandran used a mirror box which reflected the woman's left hand to make it look like she had a pair of limbs.
After two weeks of training the RN was able to extend the short fingers on her phantom limb, which relieved her pain.
Dr McGeoch, from the university's Centre for Brain and Cognition, told the New Scientist that the case of RN showed more than was previously known about the balance between the external appearance of a limb and how the brain innately believes it to look.
He said: '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.'
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