<unk>  is important in regulating<unk> . Mammalian<unk>  can be sub-divided into two distinct phases - REM (rapid eye movement) and non-REM (NREM)<unk> . In humans and cats, NREM<unk>  has four stages, where the third and fourth stages are considered slow-wave<unk>  (SWS). SWS is considered deep<unk> , when<unk>  is least active.<unk>  involves two biochemical processes that occur in living organisms. The first is anabolism, which refers to the build up of molecules. The second is catabolism, the breakdown of molecules. These two processes work to regulate the amount of energy the body uses to maintain itself. During non-REM<unk> , metabolic rate and brain temperature are lowered to deal with damages that may have occurred during time of wakefulness.
Sleep and metabolism
Brain and Behavior
Sexual motivation and hormones
Sleep and breathing
Social 
Nutrition and cognition
Mental environment
Child development