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STEVE INSKEEP, host:

More than half of all amputees say they can still feel their missing limbs, and in most cases what they feel is pain. So how do you treat pain in a limb that isn't there? That's something that our friends at Radio Lab have been wondering about.

(Soundbite of music)

JAD ABUMRAD: Hey, Steve.

INSKEEP: Hey. That's Jad Abumrad from WNYC.

ROBERT KRULWICH: And this is me, Robert Krulwich.

INSKEEP: And before we get started, we should explain what Radio Lab is for those people who don't recall.

KRULWICH: Radio Lab is a place where we explore big ideas that make us really rethink ourselves…

ABUMRAD: And the whole world around us.

KRULWICH: And this time we are thinking about how to fix an arm that isn't there.

Dr. V.S. RAMACHANDRAN (Neurologist, University of California San Diego): I am V.S. Ramachandran.

KRULWICH: He's a well-known neurologist. He works in California.

Dr. RAMACHANDRAN: The University of California San Diego.

KRULWICH: And one day, he says a patient showed up in his office, and it seems that the guy had had this arm amputated - it was his left arm - and that ever since, this man had an uncanny feeling that he still had an arm where his real arm used to be.

Dr. RAMACHANDRAN: Yes. Now, it's important to emphasize this is not a delusion. He doesn't think he has an arm. He knows he doesn't. He's not crazy. But he vividly feels its presence.

KRULWICH: And the rough part was that this arm, it hurt. This sometimes happens to people with phantom limbs. He would have days where his phantom arm would seize up in pain.

Dr. RAMACHANDRAN: Doctor, it hurts.

KRULWICH: Really badly.

Dr. RAMACHANDRAN: He goes into this painful, clenching spasm. The nails dig into my palm.

ABUMRAD: So, he has a phantom hand at the end of his phantom limb.

Dr. RAMACHANDRAN: Yes. And he'll say things like it's going to a cramp with the nails digging into the phantom palm, and it's excruciatingly painful.

KRULWICH: But there are no nails, there is no palm.

Dr. RAMACHANDRAN: There's no nail, there's no palm.

KRULWICH: And weirdest of all, the patient couldn't do anything about it. He'd tried to unclench his phantom nails from his phantom palm to make the pain stop, but he couldn't.

Dr. RAMACHANDRAN: He said I cannot move the phantom.

KRULWICH: The phantom arm wouldn't obey.

Dr. RAMACHANDRAN: I cannot volitionally move it. And I started thinking to myself, what does he mean when he says he cannot move his phantom limb? It's like an oxymoron. There is no arm there.

(Soundbite of music)

KRULWICH: Dr. Ramachandran was confused. What's going on? He checked with the patient and discovered that 11 years earlier, before the amputation, he'd had an injury to his spine. And after that, his real left arm was paralyzed. He could not move it. He tried. His brain would issue the commands.

Dr. RAMACHANDRAN: His brain was saying move the arm, but he was getting visual feedback, and indeed feedback from his muscles, saying no. Move the arm. No. Move. No.

KRULWICH: And this went on for months.

Dr. RAMACHANDRAN: Move. No.

KRULWICH: So maybe, thought Dr. Ramachandran, maybe this patient got so frustrated trying to move his real arm, that at some point…

Dr. RAMACHANDRAN: After a few months or a year, the paralysis got learned by the brain, stamped into the circuitry of the brain. And I call it learned…

KRULWICH: Learned…

Dr. RAMACHANDRAN: …paralysis.

KRULWICH: …paralysis. So even when they cut the patient's arm off a year after the accident, he still didn't get any relief because the problem wasn't in his arm. It was learned paralysis. It was in his head now.

(Soundbite of music)

INSKEEP: We're learning with the people from Radio Lab. And let me make sure I understand this. The guy's in pain because he can't move a paralyzed arm which does not exist anymore.

KRULWICH: Or so Ramachandran thought. But then he thought, maybe we can help this guy by tricking his brain into thinking the arm isn't paralyzed. But now the question is how do you trick a brain? How would you do that?

Dr. RAMACHANDRAN: How would you do that, indeed?

KRULWICH: He thought for a bit.

Dr. RAMACHANDRAN: Then I had this way of using a mirror propped inside a cardboard box.

KRULWICH: A what?

Dr. RAMACHANDRAN: A mirror propped inside a cardboard box.

KRULWICH: A mirror parked inside a…you mean, like a box…

Dr. RAMACHANDRAN: Propped up.

KRULWICH: Oh. It was kind of a Home Depot solution, really. Ramachandran took a long and skinny mirror, the kind you'd hang on a closet door.

ABUMRAD: Right.

KRULWICH: And he propped it up using a cardboard box, and then turned it sideways - placed the side right in front of the patient, like right on his nose.

ABUMRAD: So he couldn't see himself.

KRULWICH: No, couldn't see anything in the mirror yet, unless he hooked his neck around, took a peak.

ABUMRAD: Oh, okay.

KRULWICH: Otherwise, he's just looking at the side. Ramachandran says - and I want you to imagine this with me, Jad.

ABUMRAD: Sure.

KRULWICH: He says I want you to take your good arm, your real arm, okay, and stick it out in front of the mirror. So, do that.

ABUMRAD: Okay.

KRULWICH: Now, make it do what the phantom arm does. Take your good arm, make it stiff, curl your hand into a fist, dig your fingernails into your palm deeply, make it hurt. You doing that?

ABUMRAD: Yeah, it's kind of hurting.

KRULWICH: Okay. Now when I tell you, crook your head so you can look into the mirror, and on your left, just where the phantom ought to be, let's pretend that that's your phantom arm. It's cramped, it's curled exactly as you'd imagine it. So now look in the mirror.

ABUMRAD: Okay.

KRULWICH: And there's your arm. You see it there in the mirror. Your phantom arm.

ABUMRAD: Got it.

KRULWICH: Now, very slowly, keeping your eye on the mirror now, I want you to uncurl your hand.

Dr. RAMACHANDRAN: Patient says, okay. He opens his real hand. My God. And, of course, it looks like his phantom is opening. That's not surprising. He's got the mirror there. But he says, my God, doctor, you're not going to believe this. The movements have all come back. All these movements in my fingers, in my elbow, in my wrist from 11 years ago come flooding into my mind.

KRULWICH: So his pretend nails are now ungripping from his pretend palm, and the whole problem of the pretend pain goes away.

Dr. RAMACHANDRAN: Goes away. That's what he said.

KRULWICH: For how long, by the way?

Dr. RAMACHANDRAN: Till the mirror was in place.

KRULWICH: But when Dr. Ramachandran took away the mirrors, the pain came back.

(Soundbite of music)

Dr. RAMACHANDRAN: I said fine, c'est la vie, you know. And then I said, look, why don't you practice with the mirror for a few weeks every day for an hour, then maybe if you do it repeatedly, you can unlearn the learned pain.

KRULWICH: So the guy goes home, gets out a mirror. You give him a mirror to take home?

Dr. RAMACHANDRAN: Correct. And…

KRULWICH: And he does it over and over.

Dr. RAMACHANDRAN: …(unintelligible) $2, take it with you.

(Soundbite of laughter)

Dr. RAMACHANDRAN: So he takes it with him. He's delighted. And then after about another week, he phones me and he sounds all agitated on the phone. And I said what's going on? He said, doctor, you're not going to believe this. It's gone. I said, what's gone? I thought maybe the mirror was gone. He said, no, no, not the mirror. The phantom is gone.

KRULWICH: Gone, gone?

Dr. RAMACHANDRAN: That's what I said: Gone, gone? What do you mean phantom is gone? He said, well, this phantom arm that I've been having for the last 11 years, it's disappeared. Well, my initial reaction was alarm. I said, my God, does this bother you? And he said no. You know, this happened three days ago. And in the last three days, you remember the excruciating elbow pain and wrist pain I got several times a day? Well, I don't have them anymore because I don't have an arm. And…

KRULWICH: This is amputation by mirror.

Dr. RAMACHANDRAN: Yeah. So, as I tell my medical colleagues jokingly, I say this is the first example in the history of medicine of a successful amputation of a phantom limb.

(Soundbite of laughter)

INSKEEP: Reminds you that the most brilliant things are often the simplest.

KRULWICH: Yeah, absolutely.

INSKEEP: Robert, Jad, thanks for stopping by.

ABUMRAD: Hey, no problem.

KRULWICH: You're welcome.

(Soundbite of music)

INSKEEP: Our visitors in the studios there were Jad Abumrad and Robert Krulwich from the show Radio Lab, which is a production of our member station WNYC in New York City. You can explore more of Radio Lab online. Just go to NPR.org.

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