Memory athletes like Sue Jin Yang — competing here in the 17th annual USA Memory Championship in New York City in 2014 — wear headphones to block out distractions as they memorize the order of decks of cards.
Carolyn Cole/LA Times via Getty Images
"My brain used to be my best friend," says Greg O'Brien, a journalist with early onset Alzheimer's. But he can't trust it anymore, he says. Alzheimer's is, in some ways, changing who he is.
Amanda Kowalski and Samantha Broun for NPR