REM and NREM Sleep Stages: Differences and Cycle Statistics

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REM (Rapid Eye Movement) is one phase of sleep. During REM, a person’s eyes move around quickly under closed eyelids. NREM (Non-Rapid Eye Movement) is the other phase of sleep. During NREM, the eyes remain still.

The connection between REM and NREM is that these two phases make up a full sleep cycle. REM and NREM are important for sleep efficiency and quality because you need to complete them both to function at your best. Sleep efficiency is the ratio of the total time asleep to the time in bed. Good sleep efficiency is 85 percent or higher. Sleep quality refers to how restorative and restful you feel after waking up. Restful slumber requires a high sleep efficiency and high sleep quality.

Within a sleep cycle, there are three stages of NREM, followed by a fourth and final stage of REM. Most people complete five to six sleep cycles throughout the night to get enough rest. However, the point at which you wake up in a sleep cycle can also impact how well-rested you feel.

The best time to wake up is at the beginning of a new sleep cycle because you are in a lighter sleep. If you awaken in the last NREM stage or the REM phase, this could cause you to feel disorientated or groggy. The reason for this is that Stage 3 NREM is a deep sleep, while REM is when dreaming occurs.

The link between REM sleep and dreaming goes back over half a century. REM was first discovered in 1953 by Eugene Aserinsky. Aserinksky’s discovery paved the way for scientists to study more of the intricacies of sleep.

Scientists measure eye movements to study sleep stages because these movements reveal when the sleeper has entered the REM phase. The scientists use an EOG (electrooculogram) and place electrodes around a person’s eyes and on their eyelids. An EOG measures the cornea-positive standing potential in relation to the back of the eye. The EOG detects when someone enters REM sleep because it senses eye movements indicative of REM.

Brain activity also changes between NREM and REM. In NREM sleep, brain activity drops down, and in REM sleep, brain activity increases. Therefore, scientists will use an EEG (electroencephalogram) to monitor electrical activity in the brain. During an EEG test, small electrodes are placed onto the sleeper’s scalp. The electrodes detect sudden increases or decreases in the electricity of the brain cells.

The faster brain activity and eye movements were two of the major findings in Aserinsky’s research. These also became the basis for which modern science connects dreaming to the REM phase.

What is the REM Sleep Cycle?

REM sleep is not a cycle but rather the fourth stage of the sleep cycle. REM sleep follows the three stages of NREM sleep. The Rapid Eye Movement Phase is a highly neurological and physical period. During REM sleep, the eyes quickly move from side to side underneath the eyelids. Next, brain activity increases and is similar to when the individual is awake. Thirdly, breathing speeds up and becomes more irregular, and lastly, the heart rate increases.

Dreaming also occurs during REM Sleep. Dreaming is when you involuntarily experience images, ideas, scenarios, and emotions while asleep. Some dreams are pleasant, while others are more disturbing. Bad dreams are also referred to as nightmares. During the REM, the arms and legs are temporarily paralyzed to prevent the individual from physically acting out their dreams. However, some people can move their limbs during REM, which is known as REM Sleep Behavior Disorder.

REM usually begins around 90 minutes after falling asleep. The first REM stage is shorter, but your time in REM increases throughout the night.

Illustration of a Man Who Suffers from REM Sleep Behavior Disorder

What are the stages of Non-REM Sleep?

There are three stages of Non-REM Sleep and one stage of REM sleep. The stages of Non-REM Sleep and REM Sleep are as follows.

Stage 1

Stage 1 of Non-REM sleep is the beginning of the sleep cycle. It is also known as N1. During N1, the person is in a light sleep and can be woken up easily. Stage N1 usually lasts for several minutes. Your brain waves, heart rate, breathing, and eye movements slow down, and the muscles begin to relax.

Stage 2

Stage 2 of Non-REM sleep is the second stage of the sleep cycle. It is also known as N2. During Stage N2, the person is still in a lighter sleep. The heart rate and breathing continue to slow down, and the muscles relax further. Next, your core body temperature drops. You may also experience spurts of brain activity, but overall, the brain waves remain slow.

Stage 3

Stage 3 of Non-REM sleep is the third part of the sleep cycle. It is also known as N3. During Stage N3, you enter a deep sleep, and therefore, it is harder to wake up. Stage N3 is longer earlier in the night but shortens as you move through multiple sleep cycles. Your breathing and heartbeat are at their lowest rates at this time. The muscles are completely relaxed, and the brain waves continue to decelerate.

Stage 4

Stage 4 is REM Sleep and the final phase of the entire sleep cycle. It is also known as R. After completing Stages N1 through N3, the body prepares for REM sleep. Brain activity begins to quicken. As a result, eye movement intensifies as well. Breathing and heart rates also increase during REM.

What is the difference between NREM and REM?

The difference between NREM and REM is that eye movement and brain activity decrease during NREM, and they increase in REM sleep.

When you are in REM sleep, your body becomes immobile even though the brain remains active. Dreams occur during REM sleep because the neurons in the central nervous system fire up quickly and cause vivid images in your mind.

In NREM, your brain waves, heart rate, and breathing slow down until you reach a deep sleep in Stage N3. 

Why is REM Sleep more important?

REM Sleep is important because experts believe it is when memory consolidation occurs. During REM, adult-born neurons (ABNs) in the brain's hippocampus region are active. The hippocampus is the part of the brain linked to memory consolidation. As a result, researchers hypothesize that increased activity may mean memories are forming.

Additionally, research suggests that more REM sleep means better memory and cognitive abilities as you age. Insufficient REM sleep is linked to an increased risk for Alzheimer's disease and quicker cognitive decline.

Why do people need more REM Sleep for energy?

We do not need more REM Sleep for energy but rather cognitive function. Instead, Stage N3 of NREM Sleep is necessary for energy.

During Stage N3, the pituitary gland releases a hormone that prompts tissue growth and muscle repair. The pituitary gland is situated at the base of the brain. The gland also controls other hormonal glands in the body, such as the thyroid, ovaries, and testicles.

Additionally, researchers have found increased blood flow in body parts that activate the immune system during N3. Therefore, this suggests that Stage N3 is also important for immune health.

How does a sleep calculator measure REM Sleep?

A sleep calculator is a device used to calculate your ideal bedtime and wake-up based on sleep cycles. If you wake up in the middle of a cycle, you could feel groggier than usual. The sleep calculator provides you with a wake-up time that should coincide with completing a full cycle.

Most sleep cycles last about 90-110 minutes. Adults should complete five or six cycles, equating to roughly seven to nine hours of rest.

Sleep calculators can be found online or on an app. To use a sleep calculator, input the time you'd like to wake up. Then, the calculator will provide you with an appropriate bedtime. You can also input the time you'd like to go to bed, and the calculator will give you a wake-up time instead.

What is the difference between REM Sleep and Deep Sleep?

The difference between REM sleep and deep sleep is that deep sleep has the lowest brain activity, while REM has the highest. Deep sleep is also known as slow-wave sleep. ‘Slow wave’ refers to the slow pace of the brain waves during this time.

When it comes to deep sleep vs. REM sleep, the first prepares you for the latter. Brain waves, heart rate, eye movement, and breathing are slowest during deep sleep. Once you enter REM, though, they quickly pick back up again. 

The amount of deep sleep you need decreases with age. Deep sleep is restorative, and therefore, vital for growth. Childhood and adolescence are significant times of growth in a person's life. As a result, younger people experience longer deep sleep stages than older individuals.

An Athlete Laying in Bed on his Back Sleeping Peacefully Illustration

What is the REM Sleep Behavior Disorder?

REM Sleep Behavior Disorder is when a person will physically and vocally act out dreams. Normally, neurological nerve pathways block muscle movement during REM. When these pathways don’t work, the individual can experience REM Sleep Behavior Disorder. 

REM Sleep Behavior Disorder may be caused by neurological issues such as Lewy body dementia and Parkinson's disease. Men over 50, individuals with narcolepsy, and people who take certain medications are also at risk.

REM Sleep Behavior Disorder symptoms include kicking the legs, punching or flailing the arms, talking, shouting, laughing, and remembering the dream if you awaken in the middle of it.

How does REM and NREM Cycle define the sleep quality?

REM sleep occupies 20-25 percent of the total time spent sleeping, and NREM occupies 75-80 percent. However, NREM and REM are equally important for your physical and cognitive health. 

If you wake up before the end of a sleep cycle, you will cut off your amount of deep sleep or REM sleep. If you don’t get enough REM sleep, your sleep quality will decrease because REM is vital for proper cognitive function. A lack of NREM sleep will also result in decreased sleep quality because NREM is restorative for good physical health. Therefore, you should focus on completing both the REM and NREM phases for quality sleep

Sleep quantity is also vital for healthy rest. Experts recommend that adults complete five to six cycles of NREM and REM. Five or six sleep cycles is about seven to nine hours of shuteye. 

Can a bed and mattress affect REM Sleep?

Yes, a bed and mattress can affect REM Sleep. Poor mattress quality can cause pressure build-up in areas such as the hips or shoulders. These pressure points may lead to discomfort that interrupts your ability to fall or stay asleep. Therefore, invest in a comfortable mattress that conforms to your shape for good pressure relief.

The wrong mattress may also not provide enough back support. Back pain could inhibit the sleep cycle too. If your current mattress is not providing adequate support,dee find something that's a better fit. A supportive mattress should be firm enough to prevent your heavier areas from sinking since that can throw off spinal alignment. Proper spine alignment is important for preventing back or neck pain. 

Content Writer

Jill Zwarensteyn is a content writer for Sleep Advisor and is enthusiastic about providing helpful and engaging information on all things sleep and wellness.

Based in Los Angeles, she is an experienced writer and journalist who enjoys spending her free time at the beach, hiking, reading, or exploring new places around town.

She’s also an avid traveler who has a personal goal of being able to successfully sleep on an airplane someday.

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