Not simply stoic. People who rate a painful stimulus highly (left) show activation in more brain regions than those who find the sensation less aversive.

What Does 'Ouch!' Mean?

When a patient says something hurts, a doctor should believe it. That's the conclusion of the first-ever study showing that individual differences in subjective pain ratings are reflected in the way people's brains are activated.

Subjective experiences like pain are notoriously difficult to study. Clinicians often use rating scales, asking patients or research volunteers to rate a sensation from 1 to 10 for intensity, for instance. But no one knew for sure whether ratings actually reflected different experiences of pain.

So neuroscientist and psychologist Robert Coghill of Wake Forest University Baptist School of Medicine in Winston-Salem, North Carolina, scanned the brains of 17 people (eight women and nine men) while heating a spot on their legs to 49°C (about the temperature of a moderately hot cup of coffee--or unpleasantly hot dishwater) for several 30-second periods. At the same time, subjects indicated the severity of pain by moving an indicator along a 10-point scale. The subjects showed remarkable variability: The lowest was a rating of 1.5 by a male who said, crestfallen, "I heard this was going to hurt." Yet the same stimulus earned an 8.9 from a female who said the pain came close to driving her out of the study.

What was going on inside their heads? To find out, the researchers compared composites of the brain-scan data from the six highest and six lowest scorers. Both groups showed similar activation of the thalamus, the part of the brain that processes pain signals directly from the spinal cord and sends them on to higher brain centers, the researchers report online this week in the Proceedings of the National Academy of Sciences. But the high-pain responders showed much more activation in three other brain areas: the primary somatosensory cortex, which gives information on where the pain is and its intensity; the anterior cingulate cortex, involved in the emotional response to pain; and the prefrontal cortex, which processes both cognitive and emotional aspects of the experiences.

The study has "big implications" philosophically as well as medically, says pain researcher Donald Price, a neuroscientist and psychologist at the University of Florida, Gainesville. It suggests that scale ratings do reflect differences in pain, rather than the way people use scales. And it sends a strong message to clinicians, some of whom "don't really believe in pain measurement," that such ratings are valid.

Related sites
Robert Coghill's Web site
American Pain Foundation