In 1992 a retired engineer in San Diego contracted a rare brain disease that wiped out his memory.
Every day he was asked where the kitchen was in his house, and every day he didn't have the foggiest idea.
It offered proof of what the US psychologist Willian James noticed more than a century ago that humans "are mere walking bundles of habits."
Yet whenever he was hungry he got up and propelled himself straight to the kitchen to get something to eat.
Studies of this man led scientists to break through: the part of our brains where habits are stored has nothing to do with memory or reason.