What about those few exceptions to the rule: couples who are in love twenty years after marriage? Curious scientists had a look at their brain activity recently:
The Neurological Basis of True Love
They say "romantic love" was invented by the troubadors of the Middle Ages. They also say it doesn't last. But Rutgers University anthropologist Helen Fisher and colleagues reported today that functional brain imaging studies show that being "in love" transcends both culture and time.