As you sleep, your brain cycles through four stages of sleep. The first three are considered non-rapid eye movement (NREM) sleep, also known as quiet sleep. The fourth is rapid eye movement (REM) sleep, also known as active sleep.
Each sleep stage has a unique function and role in maintaining your brain’s overall cognitive performance. Some stages are also associated with physical repairs that keep you healthy and get you ready for the next day.
This article discusses the four stages of sleep. It also explains what happens during each sleep stage and what can hinder sleep.
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NREM Stage 1
The first stage of the sleep cycle is a transition period between wakefulness and sleep.
If you awaken someone during this stage, they might report that they were not asleep.
During stage 1 sleep:
- Your brain slows down
- Your heartbeat, your eye movements, and your breathing slow with it
- Your body relaxes, and your muscles may twitch
This brief period of sleep lasts for around five to 10 minutes. The brain is still relatively active and producing high amplitude theta waves, which are slow brainwaves occurring primarily in the brain’s frontal lobe.
NREM Stage 2
People spend about half of their total sleep time during NREM stage 2, which lasts for about 20 minutes per cycle.
During stage 2 sleep:
- You become less aware of your surroundings
- Your body temperature drops
- Your eye movements stop
- Your breathing and heart rate become more regular
The brain also begins to produce bursts of rapid, rhythmic brain wave activity, which are known as sleep spindles. They are thought to be a feature of memory consolidation—when your brain gathers, processes, and filters new memories you acquired the previous day.
While this is occurring, your body slows down in preparation for NREM stage 3 sleep and REM sleep—the deep sleep stages when the brain and body repair, restore, and reset for the coming day.
NREM Stage 3
Deep, slow brain waves known as delta waves begin to emerge during NREM stage 3 sleep—a stage that is also referred to as delta sleep. This is a period of deep sleep where any environmental noises or activity may fail to wake the sleeping person.
Sleepwalking typically occurs during NREM stage 3 sleep. It is more common in the early part of your night’s sleep. Children and young adults are more likely to sleepwalk than older adults.
During NREM stage 3 sleep:
- Your muscles are completely relaxed
- Your blood pressure drops and breathing slows
- You progress into your deepest sleep
During this deep sleep stage, your body starts its physical repairs. Getting enough NREM stage 3 sleep makes you feel refreshed the next day.
Meanwhile, your brain consolidates declarative memories—for example, general knowledge, facts or statistics, personal experiences, and other things you have learned.
Stage 4: REM Sleep
While your brain is aroused with mental activities during REM sleep, the fourth stage of sleep, your voluntary muscles become immobilized.
During REM sleep, your brain’s activity most closely resembles its activity during waking hours. However, your body is temporarily paralyzed—a good thing, as it prevents you from acting out your dreams.
REM sleep begins approximately 90 minutes after falling asleep. At this time:
- Your brain lights up with activity
- Your body is relaxed and immobilized
- Your breathing is faster and irregular
- Your eyes move rapidly
- You dream
Like stage 3, memory consolidation also happens during REM sleep. However, it is thought that REM sleep is when emotions and emotional memories are processed and stored.
Your brain also uses this time to cement information into memory, making it an important stage for learning.
Repair Work in Progress
During deep sleep (stage 3 and REM), your cells repair and rebuild, and hormones are secreted to promote bone and muscle growth. Your body also uses deep sleep to strengthen your immunity so you can fight off illness and infection.
Dreaming Sleep and Sleep Cycles
Sequence of Sleep Stages
It’s important to realize that sleep does not progress through the four stages in perfect sequence.
When you have a full night of uninterrupted sleep, the stages progress as follows:
- Sleep begins with NREM stage 1 sleep.
- NREM stage 1 progresses into NREM stage 2.
- NREM stage 2 is followed by NREM stage 3.
- NREM stage 2 is then repeated.
- Finally, you are in REM sleep.
Once REM sleep is over, the body usually returns to NREM stage 2 before beginning the cycle.
Time spent in each stage changes throughout the night as the cycle repeats (about four to five times total).
Sleep architecture refers to the cycles and stages a person experiences at night. A sleep specialist may show you this information on what’s known as a hypnogram—a graph produced by an EEG.
How Long Is a Sleep Cycle?
According to the National Sleep Foundation, a full sleep cycle is generally around 90 minutes long.
Factors That Affect Your Sleep Cycle
Any time you have trouble falling asleep or staying asleep at night, your sleep cycle will be affected.
Interrupted sleep is the term used to describe sleep that is not continuous throughout the night. When this happens, your sleep cycle can be disrupted. An in-progress sleep stage may be cut short, and a cycle may repeat before finishing.
Several issues can interrupt your sleep cycles. This may happen occasionally or chronically, depending on which one is at play.
Some factors that are associated with interrupted sleep and, therefore, may affect your sleep stages include:
- Older age: Sleep naturally becomes lighter, and you are more easily awoken.
- Nocturia: Frequently waking up with the need to urinate
- Sleep disorders, including obstructive sleep apnea (breathing that stops and starts during sleep) and restless leg syndrome (an intense sensation of needing to move the legs)
- Pain: Difficulty falling or staying asleep due to acute or chronic pain conditions, like fibromyalgia
- Mood disorders such as depression or anxiety
- Other health conditions including Alzheimer’s disease, Parkinson’s disease, and obesity
- Lifestyle habits: Little/no exercise, cigarette smoking, excessive caffeine intake, excessive alcohol use
What Happens When Sleep Stages Are Altered
Not spending enough time in each sleep stage or properly cycling through the stages of sleep can affect you in various ways, potentially having short-term and long-term consequences.
A few examples of issues that can arise from a disrupted sleep cycle include problems with:
- Learning and focusing
- Being creative
- Making rational decisions
- Solving problems
- Recalling memories or information
- Controlling your emotions or behaviors
People with a disrupted sleep cycle are also at greater risk for:
- Pain
- Inflammation
- High blood pressure
- Heart disease
- Overweight/obesity
- Diabetes
- Reduced quality of life
Tips For a Healthier Sleep Cycle
According to the Centers for Disease Control and Prevention, 1 in 3 adults in the US reports not getting enough sleep. There are things everyone can try to help improve the quality and quantity of sleep.
- Limit electronics before bed.
- Try to get at least half an hour of natural sunlight per day.
- Go to bed and wake up at roughly the same time each day.
- Get some exercise each day.
- Don’t eat a heavy meal before bed.
- Avoid alcohol.
- Keep your room cool and dark.
- Get adequate sleep. The longer you sleep, the more REM sleep you will get.
If you practice good sleep hygiene, you can often improve the quantity and quality of your sleep. If you still are not getting sufficient sleep after trying the above tips for at least a week, see a healthcare professional to assess if you need other assistance, such as medication or a sleep apnea device.
Summary
As your body progresses through the four sleep cycle stages—stages 1 through 3 (non-rapid eye movement, or NREM) and stage 4 (rapid eye movement, or REM), it transitions through different biological processes that affect your temperature, breathing, cells, and muscles. All the while, your brain is busy forming, organizing, and storing memories.
The sleep cycle follows a specific pattern, but that can be interrupted because of various habits, health conditions, and even older age.
Over time, not getting enough sleep and not cycling through the four stages can cause physical and mental health issues.
A Word From Verywell
The American Academy of Sleep Medicine and the Sleep Research Society recommend that adults get seven or more hours of sleep per night. But it’s important to get uninterrupted, quality sleep that allows your body to benefit from these four stages.
If you experience any of the following, make an appointment to see a healthcare provider, as you may not be getting the sleep you need:
- You are having trouble falling or staying asleep at least three nights per week
- You regularly wake up feeling unrested
- Your daytime activities are affected by fatigue or mental alertness
- You often need to take a nap to get through the day
- A sleep partner has told you that you snore or gasp when you are asleep
- Lack of sleep is affecting your mental wellbeing
10 Ways to Get a Better Night of Sleep
FAQs
The 4 Stages of Sleep (NREM and REM Sleep Cycles)? ›
Sleep occurs in five stages: wake, N1, N2, N3, and REM. Stages N1 to N3 are considered non-rapid eye movement (NREM) sleep, with each stage a progressively deeper sleep.
What are the 4 stages of NREM sleep? ›Sleep occurs in five stages: wake, N1, N2, N3, and REM. Stages N1 to N3 are considered non-rapid eye movement (NREM) sleep, with each stage a progressively deeper sleep.
What are the stages of REM and NREM sleep? ›A sleep episode begins with a short period of NREM stage 1 progressing through stage 2, followed by stages 3 and 4 and finally to REM. However, individuals do not remain in REM sleep the remainder of the night but, rather, cycle between stages of NREM and REM throughout the night (Figure 2-1).
What are the 4 stages of sleep quizlet? ›- Stage 1. Small, irregular brain waves (alpha waves); light sleep.
- Stage 2. Sleep spindles; minor noises won't disrupt sleep (beta waves)
- Stage 3. Delta waves begin; breathing and pulse slow down.
- Stage 4. ALL delta waves; deep sleep; nightmares occur here.
- REM 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.
Is Stage 4 the deepest stage of NREM sleep? ›These four sleep stages are called non-rapid eye movement (non-REM) sleep, and its most prominent feature is the slow-wave (stage IV) sleep. It is most difficult to awaken people from slow-wave sleep; hence it is considered to be the deepest stage of sleep.
Is REM or NREM deep sleep? ›Sleep is divided into two categories: REM and non-REM sleep. You begin the night in non-REM sleep followed by a brief period of REM sleep. The cycle continues throughout the night about every 90 minutes . Deep sleep occurs in the final stage of non-REM sleep.
What are stages 1 to 4 and REM sleep? ›In general, each cycle moves sequentially through each of the 4 stages of sleep: wake, light sleep, deep sleep, REM, and repeat. Cycles earlier in the night tend to have more deep sleep while later cycles have a higher proportion of REM. By the final cycle, your body may even choose to skip deep sleep altogether.
Which is first REM or NREM? ›Non-REM sleep happens first and includes three stages. The last two stage of non-REM sleep is when you sleep deeply. It's hard to wake up from this stage of sleep. REM sleep happens about an hour to an hour and a half after falling asleep.
What is Stage 4 sleep? ›Stage 4 is an even deeper sleep where the brain waves further slow and sleepers are very difficult to wake. It's believed that tissue repair occurs during the stage of sleep and that hormones are also released to help with growth.
Is Stage 4 of the sleep cycle the most restorative? ›
Stage 3 and 4 sleep, the most restorative stages, are known as deep sleep. We need about one and a half to two hours of deep sleep a night. In stage 3, very slow brain waves called delta waves are interspersed with smaller, faster waves. By stage 4, the brain almost exclusively produces delta waves.
What is Stage 4 sleep also known as sleep quizlet? ›Stages 3 and 4 are referred to as deep sleep or delta sleep, and it is very difficult to wake someone from them. In deep sleep, there is no eye movement or muscle activity. This is when some children experience bedwetting, sleepwalking or night terrors.
What occurs during REM sleep? ›Rapid eye movement (REM) sleep
During REM sleep, your eyes twitch and your brain is active. Brain activity measured during REM sleep is similar to your brain's activity during waking hours. Dreaming usually happens during REM sleep. Your muscles normally become limp to prevent you from acting out your dreams.
NREM dream reports are short and do not have a lot of detail. REM sleep has much more detailed and immersive dreams and subjects are able to recall them on a much more detailed level.
What is the difference between REM and NREM quizlet? ›The body's internal function is more active during REM sleep than NREM sleep. Heart rate is faster and more irregular, blood pressure rises and breathing is quicker and more irregular. Adults spend approx. 20% of sleep time in REM sleep.
Is REM sleep stage 3 or 4? ›| Sleep Stages | Type of Sleep | Other Names |
|---|---|---|
| Stage 1 | NREM | N1 |
| Stage 2 | NREM | N2 |
| Stage 3 | NREM | N3, slow-wave sleep (SWS), delta sleep, deep sleep |
| Stage 4 | REM | REM Sleep |
NREM sleep plays an important role in helping the body repair tissues, build bone and muscle, and strengthen its immune system. During normal sleep, a person goes through four to five sleep cycles that last about 90 minutes each and include both NREM sleep and REM sleep.
Is NREM better than REM? ›Both types of sleep are important. While experts used to believe REM sleep played the most important role in learning and memory processes, they now consider NREM sleep even more important for these functions. Plus, the most restful phase of sleep also happens during NREM sleep.
How many hours is 4 sleep cycles? ›That's because it's better to move through four full cycles (six hours of sleep) versus getting eight hours but waking up in the middle of REM sleep.
Are 4 sleep cycles good? ›Ideally, you need four to six cycles of sleep every 24 hours to feel fresh and rested. Each cycle contains four individual stages: three that form non-rapid eye movement (NREM) sleep and one rapid eye movement (REM) sleep.
What is NREM stage 4 in psychology? ›
Stage 4: REM Sleep
While your brain is aroused with mental activities during REM sleep, the fourth stage of sleep, your voluntary muscles become immobilized. During REM sleep, your brain's activity most closely resembles its activity during waking hours.
Stage 1 and stage 2 NREM sleep are considered light sleep, while stage 3 NREM sleep is considered deep sleep. Certain hallmarks of electrical activity in the brain appear during each stage. These are usually described by their frequency, or Hertz. A higher number indicates that neurons are firing more rapidly.
What is stage 3 NREM sleep? ›Stage 3 sleep is also known as N3 or deep sleep, and it is harder to wake someone up if they are in this phase. Muscle tone, pulse, and breathing rate decrease in N3 sleep as the body relaxes even further. The brain activity during this period has an identifiable pattern of what are known as delta waves.
Why are NREM stages 3 and 4 commonly referred to as slow wave sleep? ›Stage 3 and stage 4 of sleep are often referred to as deep sleep or slow-wave sleep because these stages are characterized by low frequency (up to 4 Hz), high amplitude delta waves (figuer below). During this time, an individual's heart rate and respiration slow dramatically.
What is Stage 4 sleep studies? ›Level 4 refers to Sleep Apna Screening with Oximetry, which measures blood oxygen levels; this test may also include measuring heart rate. Level 4 studies is usually used to test for Pediatric Sleep disorders.
What is stage 4 of sleep characterized by quizlet? ›Stage 4 sleep is characterized by more frequent delta waves. REM sleep is characterized by small-amplitude high frequency waves very similar to the activity of the awake brain. REM sleep is also characterized by limp, flaccid muscle tension.
What happens in non REM or NREM? ›During the three stages of non-REM sleep, a person falls asleep and then moves from a light sleep into a deep sleep. This is when a person's brain activity, breathing, and heart rate slow down, body temperature drops, muscles relax, and eye movements stop.
What is the function of NREM sleep? ›NREM sleep plays an important role in helping the body repair tissues, build bone and muscle, and strengthen its immune system. During normal sleep, a person goes through four to five sleep cycles that last about 90 minutes each and include both NREM sleep and REM sleep.
How does NREM affect sleep? ›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.
What happens during NREM 1? ›This stage of light sleeping lasts for five to 10 minutes. Everything starts to slow down, including your eye movement and muscle activity. Your eyes stay closed. If you get woken from stage 1 sleep, you may feel as if you haven't slept at all.
What happens during REM 3 sleep? ›
Rapid eye movement (REM) sleep
During REM sleep, your eyes twitch and your brain is active. Brain activity measured during REM sleep is similar to your brain's activity during waking hours. Dreaming usually happens during REM sleep. Your muscles normally become limp to prevent you from acting out your dreams.
Older classification had four stages of NREM sleep. In the current rules, NREM stage 3 and NREM stage 4 are combined as stage N3. Sleep stages occur in cycles lasting 90 to 120 minutes each. Four to five cycles occur during a typical night of sleep.
What is NREM vs REM waves? ›During REM sleep, your eyes move around rapidly in a range of directions, but don't send any visual information to your brain. That doesn't happen during non-REM sleep. First comes non-REM sleep, followed by a shorter period of REM sleep, and then the cycle starts over again. Dreams typically happen during REM sleep.