July 08, 2003
by Sanjanthi Velu
, www.sciencentral.comPainfully Real
Do different people feel the same painful experiences differently? They do.
And this ScienCentral news video reports that neuroscientists can now see the differences in our brains.Pain in Your Brain
Pain is such a personal, subjective experience that it has always been difficult to objectively measure it.
"We've all met people who seem like they're very sensitive to pain and people who seem like they're not sensitive at all to pain," says Robert Coghill, assistant professor at the department of neurobiology and anatomy at Wake Forest University School of Medicine.
And because of this difference in pain sensitivity, doctors are not always confident about the accuracy of their patients' self-reports of pain. This makes it difficult for doctors to prescribe the right dose of pain medication.
To find out if our brains reflect this difference in pain sensitivity, Coghill and his team recruited 17 normal healthy volunteers to participate in a test. They reported in the Proceedings of the National Academy of Science that they used a computer-controlled heat stimulator to heat a small patch of volunteers' skin, and allowed them to rate their sensitivity to pain on a scale of one to ten. Some said the pain was intensely painful while others said it was only mildly painful. Then they repeated the heat stimulus test while they scanned the volunteers' brains using a functional magnetic resonance imaging (fMRI) scanner.
Those who reported experiencing a lot of pain to the stimulus were considered "highly sensitive", while those who reported little pain from the same stimulus were considered "insensitive." When comparing these people's MRI scans, Coghill found that "several regions of the cerebral cortex—that's the outer layer of the brain where a lot of processing occurs—were activated more frequently and more intensely in the highly sensitive individuals than in the insensitive individuals.
"Some of these [brain] regions are involved in helping you appreciate and understand where a stimulus is on your body, and how intense a stimulus is. Other regions are important in coloring your interpretations of that stimulus, basically giving that stimulus an inherent unpleasantness that makes pain not fun."
However, the researchers found a similar level of activation in an area of the brain called the thalamus in both the sensitive and not-so-sensitive people. The thalamus is the part of the brain that receives the information and relays the pain signals to other parts of the brain.
Because of this similarity in activity in the thalamus and differences in other parts of the brain, Coghill explains that this study raises the interesting possibility that the same pain signal coming in is interpreted differently in each of our brains. "The highly sensitive people and the insensitive people were processing this painful information in a manner that is very similar in their spinal cord and peripheral nerves. But then, once that information got up to the brain it was processed and colored in a very, very different fashion".
Although Coghill says the reason people feel pain differently remains a tough question, he suggests that "a person's past experience with pain, a person's present state at the time that they're experiencing pain and also what that pain means to them, has a tremendous impact on what people actually feel.""Given that difference, it really does seem that individuals are very capable of telling us what they're feeling,"
says Coghill. So this study may help doctors and physicians have more confidence in patients' ratings of pain. Doctors may be able to identify the highly sensitive individuals and give them a higher dose of medicine while the insensitive or the less-sensitive individuals can be identified and given lower doses of pain medication.This study was funded by the National Instiute of Neurological Disorders and Stroke