Once something is ours, we fear losing it.

When people were asked to choose between an iPod and, say, $100, they were more likely to choose the money. But when they were given an iPod and then immediately asked if they would like to trade it for $100, they were more likely to leave the Ben Franklin on the table.

This is called the endowment effect, which researcher Brian Knutson of Stanford University calls "the poster child of strange (economic) behavior." Chimps exhibit the effect, too.

Watching the subjects' brains with an fMRI (neuroimaging) machine, Knutson and his colleagues found that activity in the nucleus accumbens, which signals how much we like an object, did not increase when the new iPod belonged to the subject. But the right insular, which warns us about possible loss, became more active when the iPod became my iPod.

The results are detailed in the current issue of the journal Neuron. - yahoo