A few days before the interview, I began to prepare. “What’s the day of the week today,” I asked mentally while making morning tea. “What year is this? What country?” I’ve encountered these questions before and expect to hear them again as a participant in a national aging study--basic cognition questions meant to measure mental nimbleness. On a memo pad, I jot five random words: chair, apple, yellow, letter, cottage. With the pad flipped over, I repeat them mentally. How man