Psychology Today has an interesting story on a new theory of why we dream. Finnish psychologist Antti Revonsuo believes that dreams are a sort of nighttime theater in which our brains screen realistic scenarios simulating emergency situations and providing an arena for safe training. "The primary function of negative dreams is rehearsal for similar real events, so that threat recognition and avoidance happens faster and more automatically in comparable real situations," he says. We have 300 to 1,000 threat dreams per year--one to four per night and just under half are aggressive encounters: physical aggression such as fistfights, and nonphysical aggression such as verbal arguments. Faced with actual life-or-death situations--traffic accidents, terrorist attacks, street assaults - people report entering a mode of calm, rapid response, reacting automatically, almost without thinking. Afterward, they often say the episode felt unreal, as if it were all a dream. "Dreaming is a sensitive system that tries to pay much attention to the threatening cues in our environment," Revonsuo says. "Their function is to protect and prepare us."