A woman born missing a finger and thumb on her right hand has grown them back after her hand was amputated.

The 57-year-old woman, known as RN, who was born with a phocomelic hand grew back her missing finger and thumb as a five-fingered phantom hand after her right hand had been amputated following a car accident when she was 18.

RN began to feel the sensation of her hand still being there, but with four fingers and a thumb, according to a study published in the journal Neurocase: The Neural Basis of Cognition.

Neuroscientists at the University of California in San Diego said that said that RN's experience showed that the brain has its own hardwired internal template of how the body should look like. 

However, the brain doesn't seem to produce entirely accurate representations of the missing limb and most patients report that their phantom limbs are shorter than their real counterparts, and they are usually very painful.

RN's brain wasn't relying on what it knew from the years of direct experience before the amputation when it came up with the phantom hand, rather it was getting its information from a more basic kind of intrinsic knowledge hardwired into human brains, which is that people usually have five fingers on each hand, even though her rare congenital abnormality meant she had had three.

RN reported that on her phantom hand, the preexisting fingers felt like they were all the same length they were prior to the amputation but the two new phantom fingers only felt about half of their proper length.

RN reported that her shorter phantom index finger and thumb had become painful, so Dr. Paul McGeoch and Professor V.S Ramachandran used the mirror box therapy which reflected her left hand to make it look like she had both her hands.

After two weeks of therapy, RN was able to relieve her pain by extending the shorter fingers on her phantom limb.

Study co-author McGeoch told the New Scientist that the case of RN demonstrated more than what researchers had previously known about the balance between the outer appearance of a limb and how the brain inherently believes it to look.

"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," McGeoch told New Scientist.

"It contributes to a growing literature suggesting that our conscious experience of our body is, at least in part, dependent on the intrinsic organization of the brain, rather than a result of experience," Matthew Longo at Birkbeck, University of London, told the magazine.