In Dreams, researcher Melanie Gillespie Rosen explores the biology and psychology behind dreaming. She introduces historical theories from Aristotle to Descartes and evaluates current theories on the purpose of dreams. Dreams may help consolidate memories our brains deem important while clearing out unnecessary ones, and they may reflect anxieties in our subconscious. Gillespie Rosen examines the sleep stages and explains why most of the dreams we remember occur during REM. She even explores why some people dream in color, while others dream in black and white.