Why we dream is still one of the behavioral sciences' greatest unanswered questions. Researchers have offered many theories—memory consolidation, emotional regulation, threat simulation—but a unified one remains, well, a pipe dream. Nevertheless, people continue mining their nighttime reveries for clues to their inner lives, for creative insight, and even for premonitions.
Quite simply, cognition refers to thinking. There are the obvious applications of conscious reasoning—doing taxes, playing chess, deconstructing Macbeth—but thought takes many subtler forms, such as interpreting sensory input, guiding physical actions, and empathizing with others. The old metaphor for human cognition was the computer—a logical information-processing machine.