The hippocampus’s nut-shaped dance partner is the amygdala, and it tells the hippocampus what to keep and what to throw out. It does this by translating our emotions into chemicals, causing our adrenal glands to send out bursts of memory-enhancing hormones according to the situation. If we encounter emotionally arousing input—“Look, a tiger! Ow, my arm!”—then the amygdala will strengthen that memory. If not—“Look, a pencil. I’m hungry”—then it won
