In experiments at Baylor University where people were given Coke and Pepsi in unmarked cups and then hooked up to a brain scanner, the device clearly showed a certain number of them preferred Pepsi while tasting it. When those people were told they were drinking Pepsi, a fraction of them, the ones who had enjoyed Coke all their lives, did something unexpected. The scanner showed their brains scrambling the pleasure signals, dampening them. They then told the experimenter afterward they had preferred Coke in the taste tests.

David McRaney