Why do we do the things we do? The human brain is a marvelous, mysterious piece of evolution that on one hand empowers us to be rational, self-aware and innovative. On the other, the disciplines of psychiatry and psychology are a testament to our attempts to understand the human brain and behavior. Why do we persist in believing opinions despite scientific evidence to the contrary? What exactly is déjà vu? What causes prejudice? For more than a decade, Scientific American MIND’s long-running feature “Ask the Brains” has addressed questions like these from our readers on the quirks and quandaries of human behavior, psychology and neurology. Here in Ask the Brains, Part 1, we’ve compiled 55 of the best and most interesting inquiries on the form and structure of the brain, intelligence, learning, memory and more and have enlisted professors, instructors and other experts to provide answers that are accurate, understandable and just plain fascinating.