A comprehensive consideration of the sleeping mind. Neuroscientist Ribeiro, founder and vice-director of the Brain Institute at the Universidade Federal do Rio Grande do Norte, in Brazil, offers a capacious examination of the phenomenon of dreaming. The author draws on biology, chemistry, neurophysiology, anthropology, mythology, history, literature, biography, and art—along with myriad examples of dream narratives—to create a rich history of the human mind. What is the purpose of dreaming? Is it “an evolutionary accident,” or does dreaming have implications for survival? Do animals dream? If so, why? Ribeiro reveals that “similar circadian rhythms are found in almost all living beings” and that birds and reptiles experience REM sleep, during which dreams occur. Dinosaurs, from which birds are descended, were capable of dreaming. Ribeiro maintains that prehistoric humans dreamed, perhaps about animals and stone. In antiquity, dreams were interpreted as communications from the dead or from gods—communications that Christianity deemed pagan and blasphemous. Praising Freud for focusing on the significance of dreams in understanding human experience, Ribeiro notes that traumatic dreams are monothematic rather than metaphorical. Dreams experienced by schizophrenic patients often contain more “hostile content” than those of others, and dreams vary from babies to old people, with children’s dreams “often impoverished in emotions and images.” Besides examining dreaming, the author investigates sleep overall, especially the connection of sleep to learning, creativity, and the formation of memories. Scientists differ about what happens in neural synapses during REM sleep; Ribeiro believes that synaptic remodeling occurs, during which some synapses are eliminated and others, strengthened. Although some of the molecular, electrophysiological, biochemical, and morphological discussion is daunting, much of the book is accessible. Ribeiro urges readers to spend a few minutes after waking to recall their dreams and even to engage in lucid dreaming, in which the dreamer exerts control over the dream. A stimulating and informative overview.