These are the same structures identified in various brain functions for cognition, motor control, speech, memory and consciousness. That these stages are characterized by such properties as the speed of eye movements, duration, how easy it is to awake from it, or if we remember dreams, is typical for sleep research. Sleep is mostly studied as a clinical syndrome, which is obviously important considering the widespread occurrence of sleep disorders. General anesthetics block the activity of brain chemicals involved in active signaling and sleep is characterized by a very active brain exhibiting typical brain wave patterns that differ both from a wake or anesthetized brain. Sleep deprivation impairs cognition, learning, memorization, and over prolonged periods kills.
Sleep is necessary for normal functioning of the brain.
Sleep deprivation, before one dies, causes hallucinations, mood swings, loss of memory, and impaired physical performance. An interesting effect of the immune system on the brain is well known. Strong immune reactions to fight of an infection cause drowsiness and sleepiness, possibly to slow down physical and mental activity to make metabolic energy available to the immune system. One class of immune system hormones, the cytokines, are instrumental in this synergetic mechanism between the immune system and the brain. For what has just been described, sleep is one of two fundamental brain activities that to this day are hard to come by with a reductionist or molecular approach.