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Sleep plays an essential role in developing our brains and bodies, but it isn’t just about how many hours of total sleep you get per night. According to the National Institutes of Health (NIH), the quality of your sleep and how much time you spend in each phase can affect your cognitive function and long-term health.

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What Is Non-REM Sleep?

Non-rapid eye movement sleep, also known as non-REM sleep or NREM sleep, is a period of rest that makes up most of the sleep cycle. NREM sleep is comprised of three different stages of sleep that our bodies cycle through as we sleep:

  1. Stage N1: Also known as the “dozing off” stage, this is the shortest, lightest stage of sleep. Brain activity starts to slow during this stage, but the body isn’t fully relaxed and may experience involuntary twitching. Your heartbeat and breathing also begin to slow, allowing you to quickly transition into the second stage of sleep. However, it’s easiest to wake someone at this stage.
  2. Stage N2: During this stage, you start to fall into a light sleep. Eye movement stops, your internal temperature drops, and the brain only emits short bursts of activity, known as sleep spindles. During your first cycle of sleep, this stage only lasts about 10 to 30 minutes but increases in time when you reenter the cycle later on in the night. Most people spend about half of their sleep time in this phase.
  3. Stage N3: The third stage of NREM sleep is where deep sleep occurs. Short-wave sleep, characterized by low frequency and high-amplitude delta wave patterns, is where your most restful sleep occurs. Brain wave activity and blood pressure slow, muscles relax, and your body can recover and repair itself. This stage lasts for shorter periods as the night progresses.

Why Is Non-REM Sleep Important?

Non-REM sleep is just as important as the REM stage of sleep but contributes to your health differently. NREM sleep helps your body wind down and fall into a deep sleep, which helps you feel more rested in the morning. However, getting a good night’s sleep is about more than improving daytime sleepiness. NREM sleep can help us physically heal, recover from illness, deal with stress, and solve problems. NREM sleep also plays a role in memory consolidation and can help boost the immune system.

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Where Does Non-REM Sleep Fit in the Sleep Cycle?

Your body uses circadian rhythm and sleep-wake homeostasis to help regulate your sleep. NREM sleep comprises the first three stages of the sleep cycle: dozing off, light sleep, and slow-wave sleep (SWS), also known as deep sleep. These three stages occur as you fall asleep for the first time, but your body will cycle through them another four to six times during the night. Non-REM sleep is heavier earlier in the night but tapers off as the night progresses, with your brain spending more time in REM periods of sleep instead.

What Is the Difference Between Non-REM and REM Sleep?

The main difference between REM and non-REM comes down to brain activity. While REM sleep is characterized by rapid eye movements and high levels of brain activity, non-REM sleep is the opposite.

  • NREM is more restful: NREM sleep is when our brains start to slip into a more restful state. Brain waves are slower, muscles relax, and the body enters a light sleep. NREM sleep also includes a deep sleep stage, where your heart rate and breathing slows, and body temperature drops.
  • REM sleep is closer to wakefulness: While each stage is important to a quality sleep, rapid eye movement sleep is more similar to stages of wakefulness, whereas non-REM sleep is when the body and brain are more at rest. Biologically, NREM and REM sleep is regulated by gamma-Aminobutyric acid—also known as GABA, a neurotransmitter. GABAergic neurons are responsible for promoting NREM sleep while suppressing REM sleep. Scientists have observed that people with sleep disorders have significantly lower levels of GABA activity.

Want to Learn More About Catching Those Elusive Zs?

Saw some of the best darn logs of your life with a MasterClass Annual Membership and exclusive instructional videos from Dr. Matthew Walker, the author of Why We Sleep and the founder-director of the Center for Human Sleep Science at the University of California, Berkeley. Between Matthew’s tips for optimal snoozing and info on discovering your body’s ideal rhythms, you’ll be sleeping more deeply in no time.

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