As you read these words, your eyes scan the page, picking up patterns to which your mind assigns meaning. Meanwhile your heart contracts and relaxes, your diaphragm rises and drops to control your breathing, your back muscles tense to maintain your posture, and a thousand other basic tasks of conscious and subconscious life proceed, all under the coordinated control of roughly 86 billion neurons and an equal number of supporting cells inside your skull. To neuroscientists like us, even the simple act of reading a magazine is a wondrous feat—as well as an example of perhaps the hardest problem in science today: in truth, we cannot yet fully explain how the human brain thinks and why the brain of a monkey cannot reason as we do.