A new study claims to objectively measure a person's pain levels with a "neurologic signature" from fMRI brain scans- if the results are generalizable, doctors may no longer need to rely solely on patients' reports of where, and how much, they are hurting.

Until now, reliable physiological markers of persistent pain have been difficult to find. Most doctors rely on patients' subjective self-reports according to assessments like the Wong-Baker FACES Pain Rating Scale, which asks how bad the pain is along a spectrum of six faces that range from a smiling 0, or "No Hurt," to a bawling10, "Hurts Worst."

Subjective reports of pain levels are unreliable in people who have trouble communicating, like the elderly, very young, or cognitively impaired, and it can be difficult to quantify a sensation that varies so greatly from person to person.

Now, a team of researchers from several universities has published research that identifies a "neurologic signature," or specific pattern of brain activity, in response to pain. The paper was published in the April 11 issue of the New England Journal of Medicine (NEJM).

Specifically, the signature involves a brain circuit that involves the somatosensory cortices and posterior insula, which sense the characteristics of a pain stimulus, and the dorsal anterior cingulate cortex, anterior insula, and limbic system, which signal the extreme negative feelings that come with pain. According to the researchers, the insula, is a "pivotal hub" for identifying pain and forming behavioral responses to it.

In four studies, researchers developed a procedure in which heat of varying intensities was applied to the left forearms of a total of 114 healthy participants while they lay in an fMRI brain scanning machine. The heat stimuli ranged from a warm 41.0°C, or 105.8°F, to a scalding 49.3 °C, or 120.7°F.

Each study measured a different aspect of pain. The first two studies established specific patterns of brain activity associated with intensifying physical pain from heat, comparing the fMRI activity to participants' self-reported pain levels.

The researchers used a machine learning technique to derive meaningful patterns from individual variations, and applied it to a spatial brain activity map. The resulting neurologic signature model was able to predict the intensity of pain responses in at least 94 percent of participants.

The third study explored the differences between brain activity in response to physical pain and in response to emotional pain. The participants had all recently experienced emotionally intense breakups, and completed a series of brain scans for physical pain, then another in which they were shown photos of the ex-partner who rejected them alternating with images of a close friend.

The results showed remarkable similarities in brain activity to the two types of pain, but were specific enough to isolate patterns unique to the neurologic signature of intense physical pain in at least 78 percent of cases.

In the fourth study, the researchers examined the effect of pain relief on the brain scans by giving participants intravenous injections of the potent narcotic remifentanil during the fMRI pain procedures.

Those results showed that the highest narcotic concentration dulled the neurologic signature by about 53 percent, confirming that painkillers have direct effects on the brain's perception of pain.

The fMRI pain signature can eventually supplement the commonly used Wong-Baker FACES Pain Rating Scale, which asks patients to rate how much something hurts. [Wong-Baker FACESTM Foundation ]

The findings may only have a specific brain-based signature for heat pain, but have major implications if they can be generalized to other types. It will take much more refinement before the method can become clinically useful, but they could eventually help confirm or rule out pain in patients who are unable to communicate, or in those with pathological disorders that cause chronic pain in the absence of physical causes.

"We're just beginning to scratch the surface," senior author Dr. Ethan Kross of the University of Michigan told the Los Angeles Times. Deriving neural signatures of different types of pain might eventually lead to observable signatures of other feelings as well, like anger, love, and sadness.

Study leader Tor Wager of the University of Colorado in Boulder told NPR that he's aware of the potential for the fMRI neurologic signature to override patients' feelings about their own pain, leading to insurance conflicts about pain medications or denial of aches that aren't easily read by brain scans.

In the meantime, Wager told Popular Science that he and his colleagues plan to find brain signatures for other types of pain from pressure, electric shocks, cold, and other sensations, and further explore how attention and mood might influence physical responses.

The pain studies are proof "of how functional neuroimaging may help clinicians assess clinical symptoms, such as somatic and emotional pain, that were previously thought to be impenetrable," wrote Dr. Assia Jaillard of the Centre Hospitalier Universitaire de Grenoble in France and Dr. Allan H. Ropper of Brigham and Women's Hospital in Boston in an accompanying NEJM editorial .

"Being doctors, though, we may ultimately have to acknowledge that "pain is pain" and can be reported only by the patient."