WE SAY something is “rocket science” when it is stunningly complex. But perhaps “neuroscience” would be a more apt metaphor—the more we learn about the brain, the more new questions arise. Case in point is a seemingly simple question: How do brain cells communicate? We know they use chemicals to send messages to one another. But exactly how do neurons release these neurotransmitters and then ready themselves to send out another rapid-fire message?