A rare circulatory problem required Emily Wheldon to have her left arm amputated three years ago. Her brain still thinks it’s there.
“Most days, it just feels like I’ve got my arm next to me,” she says.
The perception is so compelling that Wheldon had to train herself not to rely on the missing limb.
“When I first had the amputation,” she says, “I was trying to put my arm out to stop myself from falling.”
Now, a study of Wheldon and two other people with arm amputations may help explain why they are living with phantom limbs.
Brain scans showed that in all three, “the phantom hand representation is exactly similar to the pre-amputated hand representation,” even five years after surgery, says Hunter Schone, a postdoctoral associate at the University of Pittsburgh who started the project as a doctoral student at University College London.
The finding, which appears in the journal Nature Neuroscience, challenges decades-old research in monkeys and people suggesting that after losing sensory input from a limb, the brain dramatically reorganizes the areas linked to that limb.
“I’m not sure the [new] study really negates that research,” says Dr. Krish Sathian, the chair of neuroscience at Penn State Health, who was not involved in the research. “But the plot thickens, which is always the case in science.”
Sathian and Schone agree the finding bodes well for people who rely on a surgically implanted brain-computer interface to control a prosthetic or robotic limb. The interface depends on the brain maintaining for many years the circuits once used to move an arm, hand, or leg.
A brain map of the body
The news study involved three people who knew they were going to have an amputation because of cancer or some other disease.
Researchers performed MRI scans before and after the amputation to look for changes in the somatosensory cortex, an area of the brain that maintains a detailed map of the body.
“When you touch something with your hand, a certain region’s activated,” Schone says. “If you feel something with your toes, a different region is activated.”
Before the amputation, participants in the scanner would move their fingers, allowing scientists to see which brain regions responded. Up to five years after the amputation, participants imagined moving their missing fingers.
Earlier studies had suggested that after the loss of a hand, the brain would shift the borders of its body map. The area responding to the missing hand would shrink, while the neighboring area linked to the lips would expand.
But that’s not what the team found.
“There’s no evidence that the map of the lips is changing,” Schone says, “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.”
Earlier studies were limited because they compared the brains of people who’d already lost a limb with the brains of typical people. The new study appears to be the first to look at the same person’s brain before and after an amputation.
Prosthetic arms and phantom limb pain
Like many people who’ve had an amputation, Wheldon often feels pain in her phantom arm and hand.
“It’s like a throbbing pain that becomes quite unbearable at times,” she says. Sometimes it feels like her wrist is sore, other times it’s like her fingers are cramping.
Previous research suggested phantom limb pain was the result of changes in the brain’s body map. But the new study suggests it occurs because the map hasn’t changed, and the brain is still expecting signals from the missing body part.
“Imagine if you had a nerve that was receiving a highly detailed information for the body and suddenly now it’s receiving some strange, atypical input,” Schone says. “How the brain would deal with something like this?”
It might interpret the input as pain, he says.
If so, he says, the solution may lie in finding a new home for a nerve ending, rather than just leaving it exposed.
An unchanging body map could be a huge boost for the emerging field of brain-computer interfaces, which can allow a paralyzed person to speak or move a robotic arm.
Many of these interfaces place electrodes in the same area of the brain that maintains the body map. So they depend on that map remaining constant over many years.
The new evidence for this “offers a lot of hope for patients with neurological conditions,” Sathian says.
Emily Wheldon isn’t seeking a brain-computer interface that could control a prosthetic left arm.
But she says it’s helpful just to have a scientific explanation of why her missing limb still seems like it’s attached, and sometimes hurts.
“A lot of people don’t realize that you can actually still feel the limb,” she says, “and they’re shocked when I say I’m suffering from phantom pain.”
Wheldon has been able to control that pain with electrical stimulation and a therapy that uses a visual representation of the missing limb. And she says the phantom pain is much less severe than the pain she felt when her arm was still there.
“Back then, the pain was so intense I couldn’t look after my newborn daughter,” she says. Now she’s back at work and able to help her kids get dressed and ready for school.
Transcript:
MARY LOUISE KELLY, HOST:
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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