>> stahl: and bob petrella... >> petrella: i moved to l.a.. >> stahl: ...a tv producer and writer who serves as the collective memory, and sometimes the evening entertainment, for his friends. >> petrella: 1996, april 27th, which was a saturday. >> it was a tuesday. >> petrella: no, april 27, '96. >> don't argue, he's right. >> oh, i'm in '93. >> petrella: see? >> it was a saturday, you're right. >> he's not wrong. >> i have an almanac, and i'm wrong. >> he's not wrong. >> stahl: i must confess that when i first heard about this research, what surprised me was not that this condition existed but that it was considered so rare. that's because it sounded like a description of a friend of mine, the actress marilu henner, a star of the hit tv show "taxi." she lives with her husband and two sons from a prior marriage in los angeles. >> hey, mom? >> marilu henner: what? >> what day was valentine's day in '79? >> henner: ( sighs ) in 1979? it was a wednesday. >> and you're right. how do you... >> henner: ( laughter ) you know, you've lived with me y