Brain Structure Shows Who is Most Sensitive to Pain

Everybody feels pain differently, and brain structure may hold the clue to these differences.

In a study published in the current online issue of the journal Pain, scientists at Wake Forest Baptist Medical Center have shown that the brain’s structure is related to how intensely people perceive pain.

“We found that individual differences in the amount of grey matter in certain regions of the brain are related to how sensitive different people are to pain,” said Robert Coghill, Ph.D., professor of neurobiology and anatomy at Wake Forest Baptist and senior author of the study.

The brain is made up of both grey and white matter. Grey matter processes information much like a computer, while white matter coordinates communications between the different regions of the brain.

The research team investigated the relationship between the amount of grey matter and individual differences in pain sensitivity in 116 healthy volunteers. Pain sensitivity was tested by having participants rate the intensity of their pain when a small spot of skin on their arm or leg was heated to 120 degrees Fahrenheit. After pain sensitivity testing, participants underwent MRI scans that recorded images of their brain structure.

“Subjects with higher pain intensity ratings had less grey matter in brain regions that contribute to internal thoughts and control of attention,” said Nichole Emerson, B.S., a graduate student in the Coghill lab and first author of the study. These regions include the posterior cingulate cortex, precuneus and areas of the posterior parietal cortex, she said.

The posterior cingulate cortex and precuneus are part of the default mode network, a set of connected brain regions that are associated with the free-flowing thoughts that people have while they are daydreaming.

“Default mode activity may compete with brain activity that generates an experience of pain, such that individuals with high default mode activity would have reduced sensitivity to pain,” Coghill said.

Areas of the posterior parietal cortex play an important role in attention. Individuals who can best keep their attention focused may also be best at keeping pain under control, Coghill said.

“These kinds of structural differences can provide a foundation for the development of better tools for the diagnosis, classification, treatment and even prevention of pain,” he said.

Extended sleep reduces pain sensitivity

A new study suggests that extending nightly sleep in mildly sleepy, healthy adults increases daytime alertness and reduces pain sensitivity.

"Our results suggest the importance of adequate sleep in various chronic pain conditions or in preparation for elective surgical procedures," said Timothy Roehrs, PhD, the study’s principal investigator and lead author. "We were surprised by the magnitude of the reduction in pain sensitivity, when compared to the reduction produced by taking codeine."

The study, appearing in the December issue of the journal SLEEP, involved 18 healthy, pain-free, sleepy volunteers. They were randomly assigned to four nights of either maintaining their habitual sleep time or extending their sleep time by spending 10 hours in bed per night. Objective daytime sleepiness was measured using the multiple sleep latency test (MSLT), and pain sensitivity was assessed using a radiant heat stimulus.

Results show that the extended sleep group slept 1.8 hours more per night than the habitual sleep group. This nightly increase in sleep time during the four experimental nights was correlated with increased daytime alertness, which was associated with less pain sensitivity.

In the extended sleep group, the length of time before participants removed their finger from a radiant heat source increased by 25 percent, reflecting a reduction in pain sensitivity. The authors report that the magnitude of this increase in finger withdrawal latency is greater than the effect found in a previous study of 60 mg of codeine.

According to the authors, this is the first study to show that extended sleep in mildly, chronically sleep deprived volunteers reduces their pain sensitivity. The results, combined with data from previous research, suggest that increased pain sensitivity in sleepy individuals is the result of their underlying sleepiness.