In his 1900 book, The Interpretation of Dreams, Sigmund Freud theorized that the content of dreams is not separate from but derived from waking hours, concluding that there must, therefore, be some connection between the two; he theorized that dreams were the controlled by unconscious desires, that “a dream is the fulfillment of a wish.”  Freud, therefore, identified two types of dreams, the manifest dream—the dream as one presented, as one remembers in the morning, that must be interpreted—and the latent dream—the true dream or wish. Freud held that dreams included symbols that needed to be decoded to understand their true meaning. The theory inspired other theories of dream in the time since and has largely fallen out of favor as dreams can be interpreted in many ways.

In its place, the self-organization theory of dream proposes that, “dreams are not independently functional but rather a coproduct of the sleeping brain, reflecting the dreamer’s physiological and psychological activities such as memory consolidation [and] emotion regulation.” In effect, dreams are the brain’s processing and storing the memories of what happened during the day, guided by one’s emotions. (In terms of psychology, “the sleeping brain is a self-organizing system that can combine discontinuous and incongruous neuronal signals (i.e., different elements of dreams) into a relatively continuous narrative during sleep.”)