Telegraph | February 16, 2011
By Stephen Adams

Researchers from Oxford, Cambridge and two German universities made their conclusions after a novel experiment examining the role of conscious thought in pain perception.

First, 22 volunteers had a pain device put on their skin that was too hot for comfort.

Each then had an intravenous line attached to deliver a powerful opiate-based painkiller.

The volunteers were asked to rate the pain before any painkiller was introduced. The average score, from 0 to 100, was 66.

Then the researchers started providing the painkiller, without telling the volunteers they had done so. The average score dropped to 55.

But when the scientists told them they had started administering the painkiller the score dropped again to 39.

When they said they had stopped providing the painkiller, the score rose to 64 - even though the opiate was still flowing.

At the same time the volunteers' brain activity was monitored using MRI scans. These showed their brains' pain networks were more active when they thought the drug was not being administered, while 'positive' thoughts that the painkiller was flowing inhibited such activity.

Professor Irene Tracey of the Centre for Functional Magnetic Resonance Imaging of the Brain at Oxford University, who led the research, said: "Doctors shouldn’t underestimate the significant influence that patients’ negative expectations can have on outcome.

"For example, people with chronic pain will often have seen many doctors and tried 16many drugs that haven’t worked for them.

"They come to see the clinician with all this negative experience, not expecting to receive anything that will work for them.

"Doctors have almost got to work on that first before any drug will have an effect on their pain."

The research is published in the journal Science Translational Medicine.