Researchers say they’ve figured out an objective way to measure pain -- by imaging the brain’s response, in real time.
They used a type of brain scanner called functional magnetic resonance imaging, or fMRI, to take pictures of people’s responses to pain. And they documented that a morphine-based painkiller reduces both the pain that people reported they felt, and the pain that registered on the brain scan.
The test will be useful not as a pain lie detector test, but as a way to objectively measure pain, treatments for pain, pain in patients who can’t talk or who can’t talk well, and pain in people who are unconscious, the researchers report in the New England Journal of Medicine.
They worked out an algorithm -- a kind of computer equation -- that could directly correlate the brain images with the degree of pain that people felt.
“We can make an accurate prediction about how much pain a person is feeling,” says Tor Dessart Wager of the University of Colorado, who helped lead the four studies detailed on Wednesday.
Other pain experts say the findings look like they will hold up. "I think it will help transform pain medicine," said Dr. David Borsook of Harvard Children's Hospital, an expert on pain imaging.
Wager's team is not the first to try using fMRI to measure pain. Sean Mackey at Stanford University published a similar report in 2011 in the Public Library of Science journal PloS ONE. Irene Tracey, of Britain’s Oxford University, is among several other groups trying to finesse the technique.
Wager’s team, working with colleagues at New York University, Johns Hopkins University and the University of Michigan, got 114 volunteers to agree to have hot plates applied to their arms while undergoing fMRI.
Temperatures went from a pleasantly warm 39 degrees C (102 degrees Fahrenheit) to 49 degrees (120 F).
“We can tell which one was more painful for you with 90- to 100-percent accuracy,” Wager says. The method was so sensitive, he says, that the team, was able to tell, by looking at the fMRI alone, if a volunteer was being touched with a plate at 48 degrees or 49 degrees.
The tests also confirmed that people do perceive pain differently, Wager says. “Let’s say I give you a 48-degrees stimulus and you go ‘This is okay; I can handle it’ and I might say ‘Oh, this really hurts’,” he said. “My brain is going to respond more strongly than yours. We are using this to track what people say they feel.”
It’s an independent way to measure actual pain. “You could be saying you don’t feel so much pain just because you are stoic,” Wager said.
But, Wager said, the scans should not be used to try to prove people are faking pain. He stresses they tested only healthy people who were not feeling pain because of disease or injury. Pain caused by wounds or illness might show up differently, he says. And some types of pain, like the pain caused by fibromyalgia, might affect different brain systems, he says.
“There are different things that people call pain and multiple treatments that influence pain and we think they work through different systems,” Wager says.
“There is really still a mystery about where in all these circuits the experience actually emerges,” he said. “The brain is complicated place. It’s easy to find things that look true but aren’t true.”
Earlier, the team had reported that social pain, such as rejection, causes the brain to activate in much the same way as physical pain. They tested this idea using the fMRI. It totally failed.
“One of the experiments is one in which everybody in the study has been romantically rejected,” Wager said. They brought in pictures of their exes, and confirmed that they were feeling emotional pain when looking at them. But the pain did not show up on the fMRI in the same patterns as physical pain. “It wasn’t fooled at all,” Wager said.
And they were also able to show how pain medications worked. In one of the experiments, volunteers got a morphine-based drug while they were being given near-burns. The brain’s indication of pain changed in direct correlation with the concentration of drug in the brain, they reported.
But then something interesting happened. In one round of experiments, they hooked the volunteers up to a drip and told them they were not getting the pain drug yet. But they were. “We fooled them,” Wager says.
It’s a well-known effect of pain treatment -- when people know they are getting a pain drug, they report less pain. And the brain scan confirmed it. When people did not believe they were getting the pain medication, they reported that the burning hurt more than the brain scan indicated it hurt. In fact, their brain response was the same, whether they knew they were getting the painkillers or not.
Next up, Wager says it will be important to test different types of pain -- pinpricks or cold for example -- and to test people who are experiencing pain caused by disease or injuries.