As dreams researchers, we place a lot of emphasis on REM (or Rapid Eye Movement) sleep and tend to ignore many of the other stages of the sleep cycle. In this blog we want to take a look at the non-dream state of sleep called Deep Sleep. As compared to the better studied and more well-known stages of dream sleep, deep sleep has had very little research on it and very little is known about it.
 
The sleep cycle was first discovered and named in the 1930s. The sleep stages are comprised of three non-REM sleep cycle and then REM sleep. “Stage 1” or theta activity, the stage of sleep between wakefulness and sleep during which the muscles are active and the eyes roll slowly. Stage 2 is a slightly deeper stage of sleep in which the eyes dart back and forth and the sleeper slips into deeper sleep. The majority of sleep time in spent in Stage N2. And finally Stage 3 is the deepest sleep in which the sleeper is least responsive and aware of his or her surroundings and less likely to awake to stimuli. Early in the night, the sleeper spends more time in Deep Sleep than in REM but as the night progresses, Deep Sleep stages become shorter while REM stages become longer.
 
Deep sleep, Delta Sleep, Slow Wave Sleep, or N3 Sleep is a stage in which the sleeper disengages from his or her surroundings completely. It is incredibly difficult to wake a person from deep sleep (especially a child as I’m sure many of you have experience with). This is also the period of sleep when sleep-walking occurs—during which time the motor center of the body is awoken but the higher centers remain asleep. Deep sleep is responsible, in large part, for the feeling of restfulness. For example, a afternoon nap of only 20 minutes is unlikely to impact the ability to fall asleep in the night. This is because a short nap is unlikely to include deep sleep whereas a longer name of over an hour may cause the sleeper to have difficulty falling asleep at night.