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When someone loses an arm, they can see it's gone, but a new study finds their brain keeps on trying to interact with the missing limb. NPR's Jon Hamilton reports on a study that challenges some beliefs about the brain's ability to adapt.
JON HAMILTON, BYLINE: A rare circulatory problem cost Emily Wheldon her left arm. That was three years ago. Wheldon says her brain still doesn't know the limb is gone.
EMILY WHELDON: Most days it just feels like I've got my arm next to me.
HAMILTON: At first, she says, that was a problem.
WHELDON: I had a couple of falls 'cause I was off balance, and then I was trying to put my arm out to stop myself from falling without realizing that it wasn't there.
HAMILTON: She's learned not to do that, but Wheldon says she still feels the fingers on her missing hand, and she experiences something called phantom limb pain.
WHELDON: It's like a throbbing pain that becomes quite unbearable at times.
HAMILTON: Now, scientists are studying people like Wheldon to understand the phantom limb phenomenon. She was 1 of 3 people who signed up for a study at University College London after learning they needed to have an arm amputated. Researchers wanted to see how losing a limb might alter the brain. Wheldon had a series of brain scans, both before and after her surgery. A scientist named Hunter Schone was in charge.
WHELDON: And whilst I was in the MRI machine, he'd make me move my fingers on my right hand and then imagine moving my fingers on my left hand.
HAMILTON: Wheldon also had to purse her lips and move her toes. Schone, who is now at the University of Pittsburgh, says that allowed the team to study an area of the brain that creates a detailed map of the body.
HUNTER SCHONE: So when you touch something with your hand, a certain region's activated. If you feel something with your toes, a different region is activated.
HAMILTON: And for 50 years or so, many scientists believed the map changed dramatically after an amputation. This allowed brain cells that once interacted with the missing limb to take on other tasks. But Schone says that's not what his team found when it looked at brain maps for, say, a missing hand.
SCHONE: On every measure we could think of, we see no evidence that the phantom hand representation has changed.
HAMILTON: Even years later. Earlier studies had found indirect evidence that brain cells once devoted to a hand would begin focusing on the lips, which are right next to the hand on the brain's body map. Schone says, again, that's not what the team found.
SCHONE: There's no evidence that the map of the lips is changing, which goes completely against all of those old studies that suggest if you lose this body part, this region of the brain is going to completely reorganize.
HAMILTON: Schone says earlier studies were limited because they compared the brains of people who'd lost a limb with the brains of typical people. The new study looked at the same person's brain before and after an amputation.
SCHONE: We all like the idea of our brain being capable of dramatic reorganization, but the idea that we can get neurons to completely change what they've done for their entire lives is a myth, in my opinion.
HAMILTON: The study appears in the journal Nature Neuroscience, and Dr. Krish Sathian, chair of neurology at Penn State Health, says it makes a strong case for rethinking how amputation alters the brain.
KRISH SATHIAN: The plot thickens (laughter), which is always the case in science and makes it fun.
HAMILTON: But Sathian says he's not sure the new study negates earlier research that found evidence of brain reorganization. One possibility, he says, is that brain cells are like the workers in an office.
SATHIAN: They might be specialized and do one particular function really, really well, but they would also do a few other tasks moderately well.
HAMILTON: So a brain cell that was really good at processing information from a finger might also be able to process some information from the lips if it needed to. Regardless, Sathian says, the finding that critical brain circuits remain after an amputation is good news for patients.
SATHIAN: I think this gives us hope that we can design new treatments.
HAMILTON: For example, a prosthetic arm connected to the same brain map once used for a natural arm.
Jon Hamilton, NPR News.
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