A study published in the journal Neurocase: The Neural Basis of Cognition reports on a curious case about a woman who, following the amputation of her right hand, sprouted a phantom hand that contained five digits, including a new thumb and finger that had never been there in the first place.
Born without a thumb and finger on her right hand, the 57-year-old woman, nicknamed RN in the case study, had her whole hand amputated following a car accident at the age of 18. As generally happens to people following an amputation, RN experienced the sensation of a phantom limb — the vivid impression that the limb was still there. In some cases, the phantom limb hurts as well.
"But here's the interesting thing," said Paul McGeoch at the University of California, San Diego. "Her phantom hand didn't have three digits, it had five."
Yet those double phantom digits were perceived to be only half-size, and they came with considerable “crushing and throbbing” pain. Three decades following the amputation, McGeoch and V.S Ramachandran (also from U.C. San Diego) managed to elongate her short phantom finger and thumb to normal size using mirror visual feedback via a box that creates the visual illusion of two hands. In the process, the pain was treated as well.
"Historically, phantom pain has been difficult to treat," said McGeoch, explaining how traditional painkillers tended to fall short. "But the mirror box has shown to be effective by many trials over the years."
Authors of the case study note that a hardwired representation of a complete hand had always been present in her brain, and once the entire hand was gone, what merged was a phantom hand with five fingers, which was then further enhanced by false visual feedback from a mirror. The case demonstrates the interaction of nature and nurture in creating and sustaining body image.
Matthew Longo at Birkbeck, University of London, told New Scientist magazine that 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 organization of the brain, rather than a result of experience."