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How Much Does It Hurt? Let's Scan Your Brain

A technique for imaging the brain allowed researchers to distinguish between physical and emotional pain.
Courtesy of Tom Wager
A technique for imaging the brain allowed researchers to distinguish between physical and emotional pain.

Scientists reported Wednesday that they had developed a way to measure how much pain people are experiencing by scanning their brains.

The researchers hope the technique will help doctors treat pain better, but the work is also raising concerns about whether the technique might interfere with doctors simply listening to their patients.

Now, when someone is in pain, a doctor has no way to judge its severity except to ask questions, a method that often is inadequate.

"We all have trouble communicating our pain and other feelings under different circumstances," says Tor Wager, an associate professor of psychology and neuroscience at the University of Colorado at Boulder, who led the research.

Many people just have a hard time describing their pain. Some exaggerate how bad it is while others are too stoic and downplay their suffering. In other cases, patients are simply physically incapable of explaining what they're feeling at all.

"Kids and people who are cognitively impaired can't articulate what they are feeling in the same way as a healthy adult," says Wager, who cites stroke patients as an example.

So Wager and his colleagues decided to see if they could measure pain objectively — using a technique known as functional magnetic imaging resonance, or fMRI. They conducted a series of four experiments involving 114 adults and report their results in a paper being published in the New England Journal of Medicine.

The experiments involved measuring brain activity via fMRIs as they administered pain with a special device — a computer-controlled hot plate that can apply carefully calibrated levels of heat to someone's arm.

"It can produce a safe and very reliable source of painful input to the brain," Wager says.

The first question was whether brain scans could tell how much pain the heat was causing. "We could measure fairly accurately how much pain a person is experiencing. It is between 90 and 100 percent accurate," Wager says.

But the researchers wanted to find out if the scans could do something even harder: Tell the difference between physical and emotional pain.

"When people experience social pain, especially pain that's elicited by a recent break up, and people feel rejected in love ... that produces a brain pattern that looks remarkably similar to the pattern elicited by physical pain," Wager says.

So for the next part of their experiment, the researchers studied only people who had recently been dumped and who were still smarting over the breakup.

The researchers showed the volunteers pictures of the people who had broken their hearts, along with pictures of people who were just friends. They compared scans of what was going on in the volunteers' brains then with what happened when they were hooked up to the hot plate.

"We tested our physical pain signature, our pattern, to see whether it was fooled into believing that the romantic rejection or social pain was like physical pain," Wager says. "And we found that it wasn't."

The researchers also showed that the scans could tell when a strong prescription painkiller was working.

Taken together, Wager says, the research shows that brain scans could help study and treat pain better.

"The hope is if we could peer into people's brains, we could understand that different kinds of pain are created by very different brain systems and we could tailor our treatments to those systems," Wager says.

Other researchers praised the research. "It's fascinating," says Lynn Webster, incoming president of the American Academy of Pain Medicine. "For a long time we've tried to find objective ways to measure pain, and it's been elusive."

But Webster worries about whether brain scans for pain could be misused. Insurance companies might try to use them to avoid paying for pain drugs. Some doctors might use them to question whether their patients are telling the truth. Some may use them instead of simply listening to their patients.

"If a patient believes their doctor understands and cares about them and believes in their pain, that can have as much of a 30 percent reduction in their pain. So that connection, this belief, can be enormously powerful," Webster says.

Wager agrees that scans should be used very cautiously."The bad scenario would be you come in in pain, the physician scans your brain and says, 'Well, we don't see the pain here so we think it's in your mind. ... We don't think it's really pain,' " Wager says. "I don't think that this kind of method can or should ever be used as a pain lie detector."

Instead, Wager hopes the technology will open a helpful window into how pain works in the brain and other feelings, too.

"There's no other way to measure emotion besides asking people how they feel," Wager says. "So the broader hope is that we can take steps toward building a neuroscience of emotion that's anchored in objective neurophysiological measurements of the brain, as well as reports of emotions."

Copyright 2021 NPR. To see more, visit https://www.npr.org.

Rob Stein is a correspondent and senior editor on NPR's science desk.