Using fMRI scans of the brain, US scientists have for the first time developed a method of “seeing” pain and suggest it may lead to reliable ways for doctors to quantify objectively how much pain patients are feeling. They also propose their study may open the route to using brain scans to measure anxiety, depression, and emotional states like anger.

Lead author Tor Wager from the University of Colorado Boulder (CU-Boulder), and colleagues, report their findings online in the 11 April issue of the New England Journal of Medicine.

Current ways of measuring pain rely on patients’ subjective description, such as saying how bad it is on a scale of 1 to 10.

An objective measure of pain that uses an observable property would be very useful. It could confirm patients’ own reports, and also offer clues into how different forms of pain develop and manifest in the brain.

In a statement Wager says that, at present, there is “no clinically acceptable way to measure pain and other emotions other than to ask a person how they feel”.

For their study Wager and other colleagues from CU-Boulder, New York University, Johns Hopkins University and the University of Michigan, carried out detailed computer searches of functional magnetic resonance imaging (fMRI) scans of 114 participants’ brains. The participants had undergone fMRI scans while being exposed to varying degrees of heat from pleasantly warm to painfully hot.

The results showed there were unique neurological patterns in the brain scans.

The researchers were expecting to discover unique patterns unique to each participant. If that were the case then it would mean a person’s pain level could only be anticipated based on past scans of their brain.

But while the researchers found unique “neurological signatures” for pain in the brain scans, these were not unique to individuals but transferrable across participants.

The transferrable signatures allowd them to predict with between 90 and 100% accuracy whether a person was experiencing painful heat or nonpainful warmth (and also distinguish pain anticipation and pain recall), even with no prior brain scans from individual participants to use as a reference.

Wager, who is associate professor of psychology and neuroscience at CU-Boulder, describes what they found as “a pattern across multiple systems in the brain that is diagnostic of how much pain people feel in response to painful heat”.

He and his colleagues were also surprised that the neurological signature was specific to physical pain. Previous studies have suggested social pain, such as that felt when a person sees a photo of someone who has caused them emotional distress, produces similar brain activity as physical pain.

But in this study, the researchers did not find the same physical pain neurological signatures in brain scans of people taken while they were experiencing emotional pain from relationship breakups.

And in a last stage of the study, the researchers found the brain scans of people who had taken painkillers before being exposed to the physical pain, contained pain signatures for lower levels of pain.

Wager and colleagues conclude:

“It is possible to use fMRI to assess pain elicited by noxious heat in healthy persons. Future studies are needed to assess whether the signature predicts clinical pain.”

In other words, the findings are not enough to allow doctors to quantify physical pain as yet, but offer a good foundation to reach that end.

The team is already testing how well the neurological signatures apply to different types of pain.

Wager says they want to discover, for instance:

“Is the predictive signature different if you experience pressure pain or mechanical pain, or pain on different parts of the body?”

They also want to see if these same techniques can be used to develop measures of chronic pain. Wager says while the signatures they have identified aren’t measures of chronic pain, he expects they may form part of it, under certain circumstances:

“Understanding the different contributions of different systems to chronic pain and other forms of suffering is an important step towards understanding and alleviating human suffering,” he adds.

Funds from the National Institute on Drug Abuse, the National Institute of Mental Health and the National Science Foundation, helped to finance the research.

In a study reported recently in the journal Neuron, researchers at the University of North Carolina School of Medicine describe finding new insights into how the nervous system processes hot and cold that may explain why people with certain forms of chronic pain experience heightened responses to cold.

Written by Catharine Paddock PhD