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Woman's 'phantom limb' never existed in the first place

“R.N.” was 57 when she came to see Paul McGeoch and V.S. Ramachandran at the Center for Brain and Cognition at the University of California San Diego. She had a constant burning sensation in her right hand.

But she hadn’t had a right hand for nearly 40 years, not since it had been amputated after an auto accident at age 18. And even before that, her right hand consisted of a normal-looking little finger, the bud of a thumb, and very short, immobile, ring and middle fingers. She had no index finger. Now, though, she was experiencing feeling in all five fingers, though they did not exist, and though her index finger had never existed because she’d been born with congenital phocomelia, a condition often linked to use of the drug thalidomide in pregnancy in the 1950s and 1960s, in which bones may be shortened or absent. 

Before the amputation, she did not have the phantom pain, nor did she experience the sensation of having five fingers. After the amputation, her brain filled in five fingers -- though her phantom index finger was about half the length of her normal left hand index finger -- and the pain.

She came to Ramachandran’s lab because he’s became famous for using a simple technique to trick the brain into seeing normal limbs where none exist as a way to ease phantom limb pain in amputees. Using mirrors, subjects see the reflection of their normal limb. The brain interprets the reflection as being that of the missing or damaged limb.

Because such patients often sense that their missing limb is trapped in an uncomfortable position from which it can’t escape, the pain persists. But with the mirror system, they appear to have control over the missing limb and can retrain their brain to believe it can move the phantom limb.

While the therapy has its doubters, McGeoch and Ramachandran reported that it worked on R.N. But what explains the appearance of R.N.’s phantom fingers where none existed in the first place?

Ramachandran sees the phenomenon in terms of nature and nurture. The nurture part refers to the way we perceive our own bodies. For example, he pointed out, people suffering from untreated leprosy can suffer the gradual loss of fingers, a whole hand, even part of a forearm. But they rarely experience phantom pain or sense a phantom limb, Ramachandran believes, because their brain has time to create a new brain map of their body. Amputees are faced with a sudden loss, and no map. So the brain fills in what was once there.  

This mapping of nurture, however, is laid down "on top of preexisting templates of body imagery," Ramachandran explained, created in utero as our brains were developing, following genetic instructions. He believes that map is permanent.

R.N. was born with this permanent map in her brain, he suggested. It was overridden by the one she created as she grew up with her malformed hand. When her hand was later amputated, however, the inhibition of the congenital map was removed, and it replaced the one she’d created through life.  

After two weeks of 30-minute daily training with the mirror apparatus, R.N. reported she’d gained more control over her phantom hand and fingers -- which now seemed almost completely normal -- and her pain was significantly reduced.

The case report is published in a recent issue of the journal Neurocase.

Brian Alexander is the author, with neuroscientist Larry Young, of "The Chemistry Between Us: Love, Sex and the Science of Attraction," coming in September.