Names, car keys, birthdays, what we were just doing: These are a few of the things we all, science journalist Foer included, forget on a regular basis. After covering the 2005 USA Memory Championship, Foer (brother of author Jonathan Safran, for what it's worth) decided to train for the competition, using shuffled cards and thousand-digit integers as his weights and treadmills. But that's just the skeleton on which Foer hangs a fascinating scientific analysis of mnemonic mysteries. What we remember, he says, defines who we are. B+