Researchers in the US have discovered a new clue to why everybody feels pain differently – it could be because of individual differences in brain structure.

Writing about their findings in a recent online issue of the journal Pain, scientists at Wake Forest Baptist Medical Center in Winston-Salem, NC, describe how they compared people’s perceived pain intensity with differences in brain structure seen in MRI scans.

Robert Coghill, senior study author and professor of neurobiology and anatomy at Wake Forest Baptist, says:

“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.”

The brain contains grey matter, which processes information, and white matter, which coordinates communication among the various brain regions.

For their study, the researchers recruited 116 healthy volunteers and tested their pain sensitivity by asking them to rate pain intensity as a small area of skin on their arm or leg was heated to 120 degrees F (49 degrees C).

After the pain sensitivity test, the participants underwent MRI scans to record images of their brain structure.

The results showed that participants with the highest pain intensity ratings had less grey matter in brain regions known to be involved in internal thoughts and attention control.

These brain regions include the posterior cingulate cortex and two regions that are part of the default mode network: the precuneus and areas of the posterior parietal cortex.

The default mode network is a group of interlinked brain regions that are associated with the free-flowing thoughts people experience as “day-dreaming.”

Prof. Coghill says:

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.”

Some parts of the posterior parietal cortex are important for attention control, and Coghill suggests people who can keep their attention focused may also be better at keeping their pain under control.

He suggests findings like theirs may help develop better ways of diagnosing, classifying, treating and perhaps even preventing pain.

Meanwhile in another study, researchers found that by attaching a signal to a small molecule called saxitoxin and injecting it into rats, they could “see pain” on PET scans.