Patrick Wall transformed understanding of pain. Now he's suffering himself. Tim Cornwell reports

He is described by a colleague as the "pain man of the century". As a medical student Patrick Wall realised, with characteristic certainty, that the explanations for patients' pain offered by his lecturers were "overt rubbish" - trapped nerves, extra ribs, floating kidneys, "mechanical disorders for which there was no evidence".

It was the start of a 40-year quest to try to come up with a new understanding of suffering. Yet now, aged 74, the man credited with transforming scientific and clinical approaches to pain confronts it personally, in the form of a prostate cancer that has metastasised into his bones, particularly his back. "Fortunately my bones respond, partly to therapy against the cancer, and partly to anti-pain things. It gives me trouble a couple of days a week," he says.

Wall's personal approach to pain is the same philosophy he offers to readers of his latest book: "Try to understand as deeply as you can what's going on." Pain: The Science of Suffering amply demonstrates why Wall, professor emeritus of King's College, London, was labelled an iconoclastic outsider. Early on in his career, while professor of physiology at the Massachusetts Institute of Technology, he was hauled in front of a high-powered panel of surgeons and neuroscientists and told to stop his research. The implications of his understanding of pain as a product of mind, as the body's plan of action for dealing with a crisis, were too radical for doctors, whose treatment of patients' physical agony was based on a far more simplistic model of how the body works. "It fired a shot across my bows," he says, recalling the episode. But it did not stop his research.

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Much of Wall's book, published next month, is devoted - as his work has been - to deconstructing these old-fashioned, mechanistic misunderstandings of pain. According to these "classical" accounts, "hard-wired" nerves signal to the brain, brain signals to hand, mouth says "Ow!" But as Wall points out, where does that leave secondary pain, which accompanies swelling and protects the injured limb? Another complication is the well-known phantom limb, when amputees endure pain in a part of the body that no longer exists.

Descartes in 1640 described pain as a "sensory signalling system". Taking as his example a man's foot near a fire, Descartes suggested that the heat acted on "delicate threads" attached to the skin "just as by pulling on one end of a rope makes to strike a bell which hangs at the end". In this "dualist" approach, pain is physical and mechanistic, with the nerves of the body ringing the bell in the mind. Wall rejects this dualism; in his "modern view", stimulus may or may not lead to pain.

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The first case study in his book is of a 43-year-old Swiss army reserve major who falls down a crevasse. With one arm jammed above his head, unable to move his legs, the man supervised his own rescue. It was only later, airlifted to safety, that the full hurt of a dislocated left shoulder and broken left collar bone made itself felt.

The "gate control" theory of pain that Wall co-originated in 1965 is based on the idea that the nervous system modulates and manipulates pain, rather than passing it straight to the brain. A neural mechanism, a "gate" in the spinal cord, can open or close, partially or fully, to pain signals. Fiercely fought over and fiddled with, the theory is nonetheless regarded as having brought about a seismic shift in the study of pain.

At its heart, says Ronald Melzack, Wall's collaborator in the 1960s, is the notion that when "your attention is distracted from an injury, then you often don't feel any pain. Information is shut off." In the heat of crisis, the pain of an injury is relegated to second place to the fight or flight at hand. Wall recounts the example of former US president Ronald Reagan, shot in the chest with a 9mm bullet, shoved into his car by the Secret Service men - yet even once inside Reagan did not realise he was injured.

Wall proposes the idea of "selective attention". He suggests that at any one time, the mind can consciously process only one incoming message. "Distraction therapies" for pain thus include anything from folk remedies like hot poultices, which act as counter-stimulants, to a placebo. In 1995, a trial was carried out on 30 patients whose headaches had driven them to hospital emergency department. A third were given an aspirin-like drug, a third a narcotic, and a third a saline injection. With all three, patients reported an identical reduction of pain.

When Wall and Melzack's paper, "Pain Mechanisms: a new theory", was published 30-odd years ago, "people did not like what we were proposing", says Melzack. "It did not fit with their idea that pain should be transmitted by a straight-through line: they liked it that pain was simple, that there was a pathway for pain, that you could cut the pathway and so on." The gate-control picture was much more complicated, suggesting that the spinal cord and the brain also play an important role in regulating what gets felt.

But by 1975, the gate-control theory had made its way into the literature. It has helped make pain an established discipline, with nearly 7,000 members of the pain association and hundreds of clinics worldwide.

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Clifford Woolf, a professor of anaesthesia at Harvard Medical School who published with Wall in the early 1980s, calls him "a philosophical scientist in the sense that he designs experiments around ideas". Always on the outside, always a radical, "he's definitely a member of the establishment now", Woolf says, as a fellow of the Royal College of Physicians and of the Royal Society.

But the book keeps an edge of protest. Wall has it in for doctors who tell patients: "There is nothing wrong with you. It is all in your head." Those of us in pain, Wall says, need comfort and hope, not to be assigned "pariah status" by doctors.

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According to the US National Institutes of Health, one in seven Americans has chronic, debilitating pain. When the US public health service published guidelines for managing severe pain in 1992, 825,000 people requested copies. In Britain, 60 per cent of the population take more than a week off work for back pain during their working lives; yet a government survey found that 50 per cent of hospital patients had avoidable pain.

Part of pain's claim to be worthy of serious medical study is that "pain can kill", in the words of John Liebeskind, the late University of California neurologist. Pain can suppress the immune system and enhance the development of tumours.

But pain also protects life, as one of the queasily compulsive medical anecdotes from Wall's book shows. He describes the case of a Canadian girl with congenital analgesia, a rare condition in which children grow up with no sensation of pain. Carefully watched by her family for burns, broken bones or the appendicitis she could not detect, she nonetheless died age 22 from osteomyelitis.

After minor injuries, like a twisted ankle, pain protects the damaged joint or ligament by telling us to keep strain off it until recovery is complete. But for those with congenital analgesia, repetitive minor injuries demolish the ankles, knees, and wrists. The damaged joints become a target for bacteria to eat into the bone marrow - bringing the "hidden horror" of osteomyelitis. As Wall says, there is a lot more to understand.

Patrick Wall will speak at a symposium, "How the Brain Makes Up its Mind", at the Royal Institution, London, on July 13. Tel 0171 930 3647.

Pain is published by Weidenfeld andNicolson at Pounds 14.99.

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A life spent in pain