DOCTORS and nurses know that some people find pain harder to endure than others. Now brain scans of people exposed to exactly the same source of pain have provided the first proof that this is so 鈥� and also suggests that how much something hurts really is 鈥渁ll in the mind鈥�.
鈥淲e saw a huge variation between responses to the same stimulus,鈥� says project leader Bob Coghill of the Wake Forest University School of Medicine in Winston-Salem, North Carolina. 鈥淭he message is: trust what patients are telling you,鈥� he says.
Coghill tested the pain tolerance of 17 healthy volunteers by applying a hot object to the back of their calves. He varied the temperature from around body temperature to 49 掳C, the temperature of very hot washing-up water.
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Volunteers asked to rate the pain on a scale of 0 to 10 showed huge variations. One resilient volunteer rated pain at the hottest temperature at just over 1, whereas another could scarcely bear it at all, rating it at 8.9.
Then Coghill repeated the experiment when the volunteers were in MRI brain scanners. The scans revealed stark differences that reflected each individual鈥檚 sensitivity to pain.
Volunteers least able to bear pain showed more activity in the cerebral cortex, which is associated with higher cognitive function. Specific areas activated included the prefrontal cortex 鈥� a region linked with attention, working memory and emotion 鈥� and the anterior cingulate cortex, already linked with pain. Finally, the 鈥渓eg鈥� region lit up on the primary somatosensory cortex 鈥� a pain 鈥渕ap鈥� of the body.
None of these areas lit up in the resilient individuals, but the thalamus, which receives pain messages from the spinal cord and peripheral nerves, was active in all 17 volunteers. This suggests that the pain was not dampened en route to the brain in any of the volunteers, so all the differences must be down to what happens in the brain. 鈥淥nce the signal arrives, the cerebral cortex interprets and colours the information based on prior experience, emotion and expectation, and that鈥檚 when the differences kick in,鈥� says Coghill, whose results appear in the Proceedings of the National Academy of Sciences (DOI: 10.1073/pnas.1430684100).