Herbie Murray
Sleep researchers use the term non-REM sleep to refer to the first four stages of sleep. Non-REM sleep is characterised by a lack of rapid eye movement and is divided into four distinct stages, each one deeper than the last. The first stage, N1, is the lightest stage of sleep, where a person transitions from wakefulness to sleep. In the second stage, N2, the body temperature drops, muscles relax, and heart and breathing rates slow. The third stage, N3, is often referred to as deep sleep, where the body repairs itself. The fourth stage is REM sleep, where dreaming occurs, brain activity increases, and the body becomes temporarily paralysed.
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What You'll Learn
Non-REM sleep is characterised by a lack of rapid eye movement
Sleep researchers use the term "non-REM sleep" to refer to the first four stages of sleep. Non-REM sleep is characterised by a lack of rapid eye movement and is divided into four distinct stages, each one deeper than the last.
The first stage of non-REM sleep is referred to as drowsiness. As a person begins to fall asleep, their body's physiological processes start to slow down, and brain waves become more regular. This stage usually lasts a few minutes and may include a decrease in heart rate. The second stage of non-REM sleep is light sleep. During this stage, brain waves continue to slow down, and the person's heart rate and body temperature decrease. The third stage of non-REM sleep is deep sleep, during which the body repairs itself. The fourth stage is the deepest and most restful stage of sleep.
While non-REM sleep is characterised by a lack of rapid eye movement, dreaming can still occur during this time. Dreams during non-REM sleep tend to be more mundane and are associated with the dreamer's friendly self. In contrast, dreams during REM sleep are more vivid and intense, often including hallucinatory and bizarre content, and are associated with the dreamer's aggressive self.
Non-REM sleep plays a critical role in physical restoration and immune function, as well as memory consolidation, especially for declarative memory. Research has shown that non-REM sleep is intimately correlated with declarative memory consolidation. Participants who slept during a declarative memory task performed better after a nap or a night of sleep, compared to those who stayed awake or had more REM sleep.
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Non-REM sleep is divided into four distinct stages
Sleep researchers use the term Non-REM sleep to refer to the first four stages of sleep. Non-REM sleep is further divided into four distinct stages, each progressively deeper than the last.
The first of these stages is referred to as drowsiness. As a person begins to fall asleep, their body's physiological processes slow down, and brain waves become more regular. This is the lightest stage of sleep, and a person can be easily awakened. It typically lasts a few minutes and may include a decrease in heart rate.
The second stage is light sleep. During this stage, brain waves continue to slow down, and the heart rate and body temperature decrease further. This stage constitutes about 50-55% of total sleep time. The brain exhibits sleep spindles, which are bursts of brain activity that are thought to assist in memory consolidation.
The third stage is deep sleep. This is the most restorative stage of sleep, during which the body repairs itself. It is much harder to wake someone during this stage than in the previous two stages.
The fourth and final stage of non-REM sleep is sometimes referred to as slow-wave sleep. It is characterised by low-frequency, high-amplitude delta waves. An individual's heart rate and respiration slow dramatically during this stage, and it is challenging to wake them up.
After the four stages of non-REM sleep, the sleep cycle transitions into REM (rapid eye movement) sleep, which is associated with dreaming.
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Stage 1 is the lightest stage of sleep
Sleep researchers use the term "non-REM sleep" to designate the first four stages of sleep. These four stages are further divided into three distinct phases, with the first stage being the lightest.
As the person continues through stage 1 sleep, there is an increase in theta wave activity. Theta waves are low-frequency, high-amplitude brain waves. This stage is marked by a further decrease in muscle tension and core body temperature, as well as a slowdown in respiration and heart rate.
Stage 1 sleep is a transitional phase, and as the person progresses through it, they move towards deeper sleep. This stage is important as it prepares the body for the deeper sleep stages that follow, allowing for physical restoration and immune function.
After stage 1, the person typically enters stage 2, which constitutes about 50%-55% of total sleep time. During this stage, the body goes into a state of deeper relaxation, and brain activity exhibits sleep spindles, which are bursts of brain activity that may assist in memory consolidation.
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Stage 2 constitutes about 50-55% of total sleep
Sleep researchers use the term "non-REM sleep" to designate stages 1 to 4 of sleep. Non-REM sleep is characterised by its depth and lack of rapid eye movement. It is divided into four stages, each of which is progressively deeper than the last. Stage 2, or N2, constitutes about 50-55% of total sleep time.
During Stage 2, the body enters a more subdued state. Body temperature drops, muscles relax, and heart rate and breathing slow. Eye movement stops and brain activity slows, although there are short bursts of brain activity, or sleep spindles, which are thought to assist in memory consolidation. This stage lasts approximately 10 to 25 minutes in the initial cycle and lengthens with each successive cycle.
Stage 2 sleep is important because it allows the body to relax and prepare for deeper sleep. It is during this stage that the body temperature drops and heart rate slows, indicating that the body is transitioning into a sleep state. The short bursts of brain activity, or sleep spindles, observed during this stage are also important for memory consolidation.
The amount of time spent in Stage 2 sleep can vary depending on various factors. For example, it has been found that adolescents require 9 to 10 hours of sleep each night, but few adolescents obtain this amount of sleep. As a result, they may spend less time in Stage 2 sleep, which can impact their memory consolidation and overall sleep quality. Additionally, individuals with insomnia may not get enough total sleep to accumulate the needed time in Stage 2.
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Stage 3 is referred to as deep sleep
Sleep researchers use the term Non-REM sleep to designate stages 1 to 4 of sleep. Non-REM sleep is characterised by a lack of rapid eye movement and is further divided into four distinct stages, each progressively deeper than the last.
The deepest stage of NREM sleep is stage 3, making up about 25% of total sleep time in adults. However, babies and children need more stage 3 sleep, and the older one gets, the less they need. Without enough stage 3 sleep, one might feel tired and drained, even if they slept for a long time.
Stage 3 NREM sleep is critical to restorative sleep, allowing for bodily recovery and growth. It is harder to wake someone up during this stage, and if they do wake up, they will likely experience sleep inertia, a state of confusion or mental fog lasting about 30 minutes.
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Frequently asked questions
Sleep researchers use the term non-REM (NREM) sleep to designate stages 1-4.
Stage 1 is the lightest stage of sleep, where a person transitions from wakefulness to sleep. It typically lasts a few minutes and may include drowsiness and a decrease in heart rate.
Stage 2 constitutes about 50%-55% of total sleep. The body temperature drops, muscles relax, and heart and breathing rates slow. Brain activity during this stage includes sleep spindles, which are bursts of brain activity that are thought to assist in memory consolidation.
Stage 3 is referred to as deep sleep or slow-wave sleep, where the body repairs itself. It is much more difficult to wake someone from sleep during this stage.
REM sleep, which follows non-REM sleep, is associated with dreaming and rapid eye movement. During REM sleep, brain activity increases, nearing levels seen when one is awake. The body experiences atonia, a temporary paralysis of the muscles, except for the eyes and the muscles that control breathing.
A sleep cycle, including non-REM and REM stages, typically repeats every 90-120 minutes throughout the night. Most people go through four to five cycles per night, assuming they get a full eight hours of sleep.
