The key to a con is not that you trust the conman, but that he shows he trusts you. Conmen ply their trade by appearing fragile or needing help, by seeming vulnerable. Because of THOMAS [The Human Oxytocin Mediated Attachment System], the human brain makes us feel good when we help others--this is the basis for attachment to family and friends and cooperation with strangers. "I need your help" is a potent stimulus for action.

This is interesting. They say that all cons rely on the mark's greed to work. But this short essay implies that greed is only a secondary factor.

Previous studies have shown that participants in "trust games" took greater risks with their money after inhaling the hormone via a nasal spray.

In this latest experiment, published in the journal Neuron, the researchers asked volunteer subjects to take part in a similar game.

They were each asked to contribute money to a human trustee, with the understanding that the trustee would invest the money and decide whether to return the profits, or betray the subject's trust by keeping the profit.

The subjects also received doses of oxytocin or a placebo via a nasal spray.

After investing, the participants were given feedback on the trustees. When their trust was abused, the placebo group became less willing to invest. But the players who had been given oxytocin continued to trust their money with a broker.

"We can see that oxytocin has a very powerful effect," said Dr Baumgartner.

"The subjects who received oxytocin demonstrated no change in their trust behaviour, even though they were informed that their trust was not honoured in roughly 50% of cases."

In a second game, where the human trustees were replaced by a computer which gave random returns, the hormone made no difference to the players' investment behaviour.

"It appears that oxytocin affects social responses specifically related to trust," Dr Baumgartner said.