Why do we dream? Find out now

If dreams are the royal road to the unconscious, as Freud claimed, then that route may be a highway full of tortuous twists and turns—leading nowhere. But it affords some spectacular vistas along the way. By turns, dreams have been deemed prophecies of the future, full of meaning—if only someone could figure out what it is—or the effluence of nerve cells randomly unwinding from a busy day. Once considered a hallmark of the periodic surges of brain activity known as rapid-eye-movement sleep, dreaming now seems somewhat less bundled up; at least 25 percent of dreams are scattered through other parts of the night. Dreaming has been seen as critical for learning, or at least important for solving problems—or as nice but unnecessary. It’s an emblem of mental illness—or a safety shield deflecting it. The newest switchback on dreams comes from South African neuroscientist Mark Solms. Maybe, says Solms, we’ve been confusing cause and effect. Dreams, h...