For the first time, scientists have identified how much pain people feel by looking at images of their brains.

The findings, published in the New England Journal of Medicine, may lead to the development of methods doctors can use to objectively quantify patients’ pain.

Currently, pain intensity is usually based on patient self-reports, using an intensity scale from one to 10. Objective measures of pain could confirm those subjective reports and provide clues about how the brain registers different types of pain.

The new research also may set the stage for using brain scans to objectively measure anxiety, depression, anger or other emotional states.

“Right now, there’s no clinically acceptable way to measure pain and other emotions other than to ask a person how they feel,” said Tor Wager of the University of Colorado and lead author of the paper.

“These findings demonstrate that it is possible to accurately predict people’s experience of an incredibly complex psychological state — an emotional response — based on neural activity alone,” said U-M psychologist Ethan Kross, a faculty associate at the Institute for Social Research and a co-author of the study.

“They raise the tantalizing possibility that it may be possible to predict the experience of other types of complex emotional responses — for example, depression or anxiety — using similar methods.”

Wager, Kross and colleagues used data-mining techniques to comb through images of brains taken when the subjects were exposed to multiple levels of heat, ranging from pleasantly warm to painfully hot.

“We found a pattern across multiple systems in the brain that is diagnostic of how much pain people feel in response to painful heat,” Wager said.

Initially, the researchers expected that pain signatures would be unique to each individual. If that were the case, a person’s pain level could only be predicted based on past images of his or her individual brain. But, instead, they found that the signature was uniform across people. This uniformity allowed researchers to accurately predict how much pain the applied heat caused each person, with no prior brain scans needed as a reference point.

The scientists also demonstrated that the signature was specific to physical pain. Past studies have shown that social pain can look very similar to physical pain in terms of the brain activity it produces.

But when Wager’s team tested to see if the newly defined neurologic signature for heat pain would also pop up in the data collected earlier from heartbroken participants, they found that the signature was absent.

“Although social and physical pain are clearly related in terms of the specific areas of the brain they recruit, distinct patterns of neural activity or neural signatures may predict each type of experience,” Kross said.