"Sleep...knits up the raveled sleave of care." William Shakespeare
On average, we are asleep for a third of our total life span. In addition to its overall restorative role, sleep also simultaneously engages and restores the brain. Sleep researchers have discovered that the brain is surprisingly active during sleep.
Dream theories developed by Freud suggest that dreams are psychological, revealing hidden urges, for example. Later research argues that dreams are physiological, beginning with random electrical impulses deep within the brain stem.
Sleep researchers use electroencephalograph (EEG) technology to trace brain waves in observations of people during night-long sleep sessions. These brain waves point to predictable sleep cycles that occur every 90 minutes. Rapid Eye Movement (REM) cycles reoccur throughout the night, accompanied by rapid, irregular changes of low electrical voltage in the brain. It is during REM sleep that we tend to dream. Newborns spend over half of their time in dreaming sleep.
Drs. Robert McCarley and J. Allen Hobsen of Harvard Medical School developed the activation synthesis theory. Every 90 minutes during sleep, an automatic activation system turns on for 30 minutes. During this time, the part of the brain called the pons sends electrical charges to the forebrain. According to activation synthesis theory, the impulses, or charges, are bits of information stored in the brain, which are fired off without explicit order or meaning. The brain takes these bits of information and tries to make sense of them, knitting them together to form a narrative or story.
Another theory combines both the psychological and physiological functions of dreams, suggesting that stored memories, concerns, emotions, and expectations are activated by the brain during sleep, and the mind works to interpret them.
Although they have varying points of disagreement, all three theories reveal that the brain is very active, even during sleep.