'Torture' study gives pain insight

The study shows how the brain copes with pain

Volunteers allowed themselves to be tortured by scientists to gain a new insight into managing pain.

The findings go some way towards explaining how soldiers being questioned under torture and martial arts experts can cope with extraordinary levels of pain.

The researchers hope their work will lead to a greater understanding of chronic pain and new ways to treat it.

This may help explain why some people are more sensitive, or less sensitive, than others when it comes to painful sensations

Dr Jon-Kar Zubieta, assistant professor of psychiatry at Michigan University Medical School

Periods of pain

The volunteers agreed to have salt water injected into their jaw muscles, copying a painful condition called temporo-mandibular joint disorder (TMJ).

Unlike previous studies, where the pain has been limited to just a few seconds, the volunteers at the University of Michigan at Ann Arbor, in the US were subjected to 20 minutes of pain.

At the same time an imaging technique was used to monitor chemical activity in the brain and volunteers were asked to rate how much pain they were feeling every 15 seconds.

The findings, published in the journal Science, showed a brain chemistry response that was strongest in areas where sensation and emotion are rooted.

The slow increase of jaw muscle pain caused a surge of pain-dulling opioid chemicals - the brain's own version of morphine - to be released.

These chemicals, known as endorphins, acted on specific receptors - molecular triggers - on the surfaces of neurones causing them to block the spread of pain messages.

The particular receptor studied, the "mu opioid receptor", is a target for both the body's own painkillers, and drugs such as heroin, morphine, and methadone, as well as anaesthetics.

Differences

Dr Jon-Kar Zubieta, assistant professor of psychiatry at Michigan University Medical School, who led the research, said: "The higher the level of activation, the lower the scores the volunteers gave for pain-related sensations and emotions, like feelings of the unpleasantness of pain."

There were wide differences between individuals in the intensity of the anti-pain brain response.

Some volunteers showed a dramatic response, and appeared to suffer and respond emotionally the least, while others were far more affected by pain.

"This may help explain why some people are more sensitive, or less sensitive, than others when it comes to painful sensations," said Dr Zubieta.

"We show that people vary both in the number of receptors that they have for these anti-pain brain chemicals, and in their ability to release anti-pain chemicals themselves. Both of these factors appear to determine the emotional and sensory aspects of a painful experience."