Pain all in the head for most

People who say they are sensitive to pain are not just being big babies - they really do feel more pain, research shows.

Brain images show that people who report feeling more pain - in this case to heat - also have more of a reaction in the brain.

The findings may offer an objective way to measure pain - something that has eluded doctors for centuries. But then again, it may be enough simply to ask the patient, said Robert Coghill of the Wake Forest University School of Medicine in North Carolina.

"You don't need an MRI scan costing several hundreds of dollars. You simply have to ask them," Coghill said.

"How they feel about the pain is their pain."

The team , used functional magnetic resonance imaging to take a "live" look inside the brains of 17 volunteers.

They applied a hot - 49-degree - thermode to the backs of volunteers' legs.

The most sensitive volunteer gave a pain rating of 8.9 out of 10 points and the least sensitive gave it just a 1.05.

The images showed more activity in three areas of the brains of the most sensitive men and women - the primary somatosensory cortex, anterior cingulate cortex and prefrontal cortex.

All are involved in perceiving pain, the researchers report in this week's issue of the Proceedings of the National Academy of Sciences.

Coghill said the input to the brain, like the actual heat applied, did not vary among the different people.

"What is happening is there is one brain region called the thalamus that is taking input from the spinal cord and distributing it to different brain regions. In the thalamus we didn't see any differences between highly sensitive and insensitive individuals.

"So this suggests basically that what is happening is that once this information goes beyond the thalamus and the brain really comes into the picture, that is where these individual differences really emerge."

They said the role of the prefrontal cortex was not clear.

- REUTERS