Diagram of the human brain in profile with shading representing areas active during REM sleep. Inside the brain at the top of the brain stem, a shaded area is labeled arousal. Toward the front of the brain stem are shaded areas labeled memory formation and emotion. A shaded area at the front of the brain contains a region labeled motivation and continues around the front to the top of the brain, containing a region labeled attention. At the back of the brain, an area labeled complex visual processing is shown within a shaded area shown wrapping down and around behind the brain stem.