N1 sleep is the first stage entered when taking a nap. Body temperature decreases, and brain waves, if observed on an electroencephalogram (EEG) in a sleep lab, would be seen to slow.Ī person can be easily awakened from N1 sleep, and that individual may not think he or she had been asleep, Quan said. During this stage, heart and breathing rates begin to slow, eye movements also slow, and muscles relax. This is a relatively light form of sleep that lasts about 5 to 10 minutes. In this first stage of non-REM sleep, a person is making the transition from being awake to falling asleep. When a person gets drowsy, he or she is drifting into N1 sleep, Quan said. Live Science asked Quan for a more detailed explanation of what happens in the body and brain during each of these four stages of sleep.
#REM SLEEP VS DEEP SLEEP VS LIGHT SLEEP SERIES#
As sleep progresses in a series of four to five sleep cycles throughout the night, the time spent in the REM stage gets longer and the time spent in N3 sleep gets shorter, Quan said.
This sequence changes somewhat between the first and second half of sleep. Those were combined into one stage, now referred to as N3.ĭuring sleep, the brain repeatedly cycles through four distinct stages of REM and non-REM sleep in a specific sequence. Before 2007, non-REM sleep was broken down into four stages, but then sleep medicine specialists decided that there was no physiological reason to distinguish between two of the stages, the old stage 3 and stage 4 sleep, he explained. Non-REM sleep is now considered to consist of three stages, known as N1, N2 and N3, Quan said.
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