Like truth and beauty, pain is subjective and hard to pin down. What hurts one moment might not register the next, and our moods and thoughts color the experience of pain. According to a report in April in the New England Journal of Medicine, however, researchers may one day be able to measure the experience of pain by scanning the brain—a much needed improvement over the subjective ratings of between one and 10 that patients are currently asked to give.
Led by neuroscientist Tor Wager of the University of Colorado at Boulder, researchers used functional MRI on healthy participants who were given heated touches to their arm, some pleasantly warm, others painfully hot. During the painful touches, a scattered group of brain regions consistently turned on. Although these regions have been previously associated with pain, the new study detected a striking and consistent jump in their activity when people reported pain, with much greater accuracy than previous studies had attained. This neural signature appeared in 93 percent of subjects reporting to feel painful heat, ramping up as pain intensity increased and receding after participants took a painkiller.
The researchers determined that the brain activity specifically marked physical pain rather than a generally unpleasant experience, because it did not emerge in people shown a picture of a lover who had recently dumped them. Although physical pain and emotional pain involve some of the same regions, the study showed that fine-grained differences in activation separate the two conditions.
A brain-based marker of pain might someday help doctors assist people who have difficulties communicating, such as the very young or victims of stroke. Yet Wager does not see this neural signature as a pain "lie detector." "There are many psychological and physiological ingredients that go into a person's report of pain, and we've discovered just one ingredient here," he says. Many states of brain activity very likely give rise to pain, Wager adds, "pain is not just one thing."