Health: Pain. Is it all in your head?

If someone points a gun at you, you're unlikely to notice your chronic arthritis.

A study has revealed that parachutists who are gently tortured before they jump don't feel a thing. Researchers suggest that they become so focused on their mission that they fail to realise that they've been given an electric shock. Doctors have also found that their bodies produce large amounts of natural opiates, which block out the pain and allow them to focus on a successful landing.

This study, and a growing body of other research, indicate that pain is far more complex than was once thought; it is not simply an automatic reaction when tissue is damaged. Perceptions of pain are now known to vary between cultures, personality types and individuals, and between people of different intellects. How people feel pain can be influenced by experiences in childhood, by seeing how parents cope with it, by cultural beliefs, and by stress.

Many people who suffer terrible injuries do not feel immediate pain, because they are preoccupied with other tasks that are seemingly more pressing. Battlefield medics have found that soldiers with the most horrendous injuries are more likely to complain about the pain of an injection than about their wounds. They see the needle going in, and expect it to hurt (but may not have seen the bullet entering their body).

The research suggests that, at least in some circumstances, the mind can triumph over matter. It is this concept which is leading to new strategies for helping patients cope with chronic pain.

The pain process begins when the sensory end of a nerve fibre detects changes in the surrounding tissue. It fires off a series of warning impulses that travel along the fibres at speeds of up to 200mph to warn the brain that something is wrong. For many years it was assumed that these nerve fibres were hard-wired directly to the brain, like a telephone line to the exchange, and that the level of pain was proportional to the extent of the tissue damage.

However, the latest theory is that there are natural pain inhibitors that can block these pain signals, as well as naturally occurring opiates whose production is triggered to relieve pain. Somewhere along the line the pain signal may be moderated or enhanced by other factors, including stress, mood, anxiety, memories of previous pain, and what the person is doing at the time.

"The best generalisation we can make is that human beings, and animals too, behave in the way that is appropriate and useful in given circumstances. If it is desirable to escape danger, to complete a task or to assist other people, then this objective would be defeated were we to allow consciousness to be dominated by pain," says Professor Patrick Wall, who is founder and editor of the medical journal Pain, and author of Defeating Pain.

He suggests that, under certain conditions, an overriding mechanism for blocking pain signals kicks in. For example, if someone is threatened with a gun they will forget their chronic arthritic pain.

Professor John Loeser, co-author of a report on pain in The Lancet, says that the central nervous system modifies signals as they travel from injured tissue to the higher brain centres to make us conscious of pain. The way different individuals experience pain can, he says, be shaped by physical changes in their nervous system brought about by learning and by experience.

Professor Loeser, of McGill University, Montreal, explains: "There are fibres coming from this inhibitory system that go down the spinal cord to every level, and which are able to stop the transmission of nerve impulses."

Anxiety and stress can enhance the perception of pain, while cultural factors can reduce it.

"Cultural factors play an important role in the way we respond to pain", says Professor Loeser. "For example, in a trephination in Africa, a man may have his scalp penetrated and skull scraped. He will sit calmly while this takes place, although the pain would make us run away. What is happening here is that mechanisms in his cortex are evaluating the situation, and they are saying that something good is being done."

He adds: "Women in labour also have different experiences of pain. We know there are biological differences, such as the size of the baby and the mother, but there are other factors too. There will, for example, be women who will refuse to take any kind of drug because it might affect their babies and that, too, could trigger the pain inhibition system."

Doctors are increasingly using psychological strategies, including distraction and preoccupation techniques, to help sufferers, he says.

"Distraction is very powerful. Being helped to visualise that you are lying on the beach, and that a log in the sea is your pain and it is floating away, can help," he states.

Chris Main, professor of behavioural medicine at Hope Hospital in Salford and Manchester University, believes that there is some way to go before the pain puzzle is solved, although the pieces are slotting into place. "Things happen in the brain as a result of an event and we cannot really understand what is happening," he says. "We know that people feel pain in the absence of injury, and we know that in certain situations the brain shuts out pain."

That is what happened to the then US President Ronald Reagan, when he was shot in the chest by a would-be assassin in 1981. When he had gunned down the baddies in his films, the actors would clutch at their wounds, cry out in pain and slump to the ground. But when Reagan was shot in the chest in real life, he showed no signs of having been hit by a bullet; he was able to walk and talk as if nothing had happened. He felt no discomfort, and at the time was more concerned about the jostling he was getting from security men as they bundled him into a car.

Attempts to harness natural pain inhibitors may lead to new therapies, but experts warn that it is important to remember that pain is there for a purpose, to warn us that something is wrong. In rare cases where babies are born without any pain-detecting devices, they may happily chew off fingers, sustaining irreversible damage without realising that anything is amiss.

"We're not trying to fix something that is broke," concludes Dr Chris Eccleston, of Bath University. "We're trying to control a system we rely on, to tell us of dangers."

Pain Relief: From Acupuncture to Opiates

Non-steroidal anti-inflammatory drugs (NSAIDs): These are the most widely used drugs. The most commonly used is aspirin. They work by blocking the body's production of prostaglandins, which start the inflammation process that leads to swelling and pain.

Steroids: Much more powerful than NSAIDs, they can be injected to target local joint pain. Cortisone is the most commonly used.

Local anaesthetics: These work like roadblocks on the nerve fibres to stop pain messages getting to the central nervous system. Used in minor surgery and by dentists to isolate the areas they are working on.

Opiates: These range in power from codeine (weak) to morphine (strong). Effective in dealing with pain caused by cancer.

Hypnosis: Thought to work by removing the anxiety associated with pain. A small number of people have opted for minor operations under hypnosis (including one who had a vasectomy). The reported effects may explain why people in trances, induced by chanting or other means, feel no immediate pain.

Acupuncture: Has been used extensively for pain relief. One theory is that when a needle is inserted into the skin or a muscle, a nerve impulse is fired off to the spinal cord which then produces endorphins, the body's natural opiates.