When it comes to pain, some people are tougher than others. New findings suggest that these differences are all in the head. Research published online this week by the Proceedings of the National Academy of Sciences show for the first time that variation in how people perceive pain results from differences in brain activity.

Robert C. Coghill of Wake Forest University and his colleagues scanned the brains of people exposed to heat from a computer-controlled pad. The temperature was increased to 120 degrees Fahrenheit, a temperature that many people find distressing, but the subjects reported varying experiences of pain--from one to nine on a 10-point scale. Those individuals more sensitive to pain exhibited greater activity in two regions of their brains involved in processing the perception of pain, the anterior cingulate cortex and the primary somatosensory cortex, than did those more impervious to pain. "One of the most difficult aspects of treating pain had been having confidence in the accuracy of patients' self-reports of pain," Coghill says. "These findings confirm that self-reports of pain intensity are highly correlated to brain activation and that self-reports should guide treatment of pain."

The results also shed light on how differences in pain sensitivity arise. "This finding raises the intriguing possibility that incoming painful information is processed by the spinal cord in a generally similar manner," Coghill notes. "But once the brain gets involved, the experience becomes very different from one individual to the next."