American Association: Sensation - Woman who couldn't help laughing

A WOMAN who could not stop laughing each time doctors stuck a needle in her skin has helped scientists to explain why we laugh - it is nature's way of signalling that a potential threat is no big deal.

Evolutionary biologists have long puzzled over why humans laugh but Vilayanur Ramachandran, professor of neuroscience at the University of California, San Diego, believes it is a way for people to alert others that a fearful situation is a false alarm.

To explain his theory, Professor Ramachandran told the American Association for the Advancement of Science of a patient, a women in her fifties, who suffered an unusual form of a condition called pain asymbolia, in which people report that they feel pain but it does not hurt them.

The woman also could not help laughing each time she experienced a painful stimulus. "She would laugh uncontrollably each time I would stick a needle into her and when I asked why she said `I don't know'," Professor Ramachandran said.

Brain scans revealed a stroke had damaged the part of the brain that received signals from the skin, which meant the pain stimulus was not passed on to the part of the brain that registers hurtful experiences.

Professor Ramachandran said this meant the woman's brain was aware something potentially painful was happening to her but that this was apparently no big deal as it did not hurt. He believes this follows the recipe for a good joke, which is why she ended up laughing.

"If you look at all jokes and humour you notice they follow a certain pattern, which is especially obvious in slapstick. You take the listener along a garden path of expectation by building up the story. At the very end you introduce a twist or anomaly which entails a complete reinterpretation of everything that has been said before. You call it the punch line," he said.

A man slipping on a banana who cuts his head badly is not amusing, but if he gets up without any harm done, it is funny. "In the second case the brain is fooled but there is no big deal. It is a false alarm.

"The question is: why should you laugh and produce this hysterical sound?

The reason I think is that you are alerting other members of your kin saying, `Look there has been a false alarm here don't waste your resources rushing to help'. Laughter is nature's OK signal, just as a baby's cry is an alarm signal."

The theory is the only way of explaining the patient's unusual response and might be why laughter is so universal, Professor Ramachandran said. "One part of her brain is saying, `Look there is pain' while at the same time the other part is saying, `That's no big deal'.

So the two key ingredients - potential alarm and no big deal - are fulfilled in her and so sh e starts laughing uncontrollably," he said.