LONDON - Scientists have shown for the first time that newborn babies have a "unique" nervous system that makes them respond differently to pain from adults.

In research that has far-reaching implications for the medical and surgical treatment of infants, the experts have found that newborn children feel pain longer and more sensitively.

And in premature babies, the mechanism that allows older children and adults to "dampen down" the pain messages does not work properly.

Until now it has been presumed that a baby's pain system was too immature to function properly, or that they reacted in a similar way to adults but less efficiently.

Researchers at University College London have discovered that babies' sensory systems have a unique pain-signalling mechanism, which disappears as they grow older. This makes them feel pain sooner than an older child or adult and, because of different "wiring," they can react to stimulation as if it is pain - even when it is not.

It is only in the last 10 years that it has even been acknowledged that babies and infants felt pain.

Surgery without drugs

Before that, babies born prematurely - after less than 30 weeks of pregnancy - would undergo traumatic or surgical procedures without pain-killing drugs.

Ticky Wright, of the Women and Children's Welfare Fund, set up to promote research into pain relief of the unborn child, welcomed the new research.

"I call this the 'oops' syndrome. First we were told that infants did not feel pain, then that the newborn baby did not, then that a fetus did not," Wright said.

"Each time it is looked at, the boundaries are pushed further and further back. Yet masses more research needs to be done."

Maria Fitzgerald, a professor of developmental neurobiology at the Thomas Lewis Pain Research Centre, based at University College, said the work has shown the importance of adequate pain relief for infants and children.

Writing in the Medical Research Council's journal, Fitzgerald said: "Reports in clinical and psychological literature indicate early injury or trauma can have long-term consequences on sensory or pain behaviour that extend into childhood or beyond."

Fitzgerald said that because the spinal sensory nerve cells worked differently in babies, even a simple skin wound at birth could lead to the area becoming hypersensitive to touch long after the wound had healed.

By studying these sensory nerve cells in infants the scientists discovered that their reflex to pain or harm is greater and more prolonged than that of adults. The sensory nerve cells are also linked to larger areas of skin, which means they feel pain over a greater area of their body.