The study of "phantom limb" feelings is providing invaluable insights on how the brain is structured and creates experiences including that of pain, Prof Ronald Melzack of McGill University, Canada, told the conference.
The latest research on people born without part of their limbs confirms they experience phantom feelings, similar to those felt by people who have lost a limb. Some 20 per cent of people with congenital limb loss have phantom experiences, while a fifth of these feel occasional pain, say in a hand that does not exist.
The phantom body, he said, could make them reach out to pick up a phone though they have no arm to do so. The brain creates the perception of the whole body even when parts of it are missing. It is a creative organ, capable of generating perceptions in the absence of sensory stimuli. "This finding is extremely important. The brain itself can generate every quality of experience, including pain, which is normally triggered by sensory input."
Yet patients in the 1950s who suffered chronic pain without presenting signs of organic disease were often sent to the psychiatrist, noted Prof Melzack.
Psychological factors previously dismissed as "reactions to pain" are now seen as an integral part of "pain processing". This has opened up new avenues for pain control. Cutting nerves and pain pathways was gradually replaced by a host of methods to modulate the input of pain from the body to the brain.
The challenge ahead is to further explore the brain's role in pain, he said. Research on phantom pain indicated neural networks representing our bodies were "genetically pre-wired into the brain". These could be triggered, leading to feelings such as pain even in the absence of the normal input from the body. The body is also perceived by the brain as "a unity", so a phantom leg moves in unison with the rest of the body. Thus, a phantom foot could feel wet if the rest of the body steps into a puddle.
Dr Declan O'Keeffe, anaesthetist and director of pain management services at St Vincent's Hospital, Dublin, said improved diagnosis of chronic pain, notably the use of precise pain block procedures - now used in validating chronic neck pain, for example - helped remove a lot of uncertainty for patients. New techniques, such as rhizotomy procedures, which involve the burning of nerves, could ease chronic pain significantly though not necessarily cure it.