Why can't you remember where you put your keys? Or the title of the movie you saw last week? Anyone older than forty knows that forgetfulness can be unnerving, frustrating, and sometimes terrifying. With compassion and humor, acclaimed journalist Cathryn Jakobson Ramin explores the factors that determine how well or poorly one's brain will age. She takes readers along on her lively journey—consulting with experts in the fields of sleep, stress, traumatic brain injury, hormones, genetics, and dementia, as well as specialists in nutrition, cognitive psychology, and the burgeoning field of drug-based cognitive enhancement. Along the way, she turns up fresh scientific findings, explores the dark regions of the human brain, and hears the intimate confessions of high-functioning midlife adults who—like so many of us—are desperate to understand exactly what's going on upstairs.