REM sleep: What is it and how it affects your brain

Rapid Eye Movement (REM) sleep represents a unique and complex stage of sleep, marked by an array of physiological changes and a heightened level of brain activity, rivaling that of wakefulness.

The importance of REM sleep can hardly be overstated. It plays a vital role in physical and mental health and has been associated with cognitive performance, memory retention, mood regulation, and creativity.

Moreover, disturbances in sleep patterns are associated with several sleep and mental health disorders, making this stage a crucial focus for medical research. 

In this article, we will explain the complex science of REM sleep. We’ll discuss the mechanisms, significance, and potential effects on human health and behavior.

What are the five stages of sleep

1. Light sleep

The first stage of sleep, often referred to as the transitional or light sleep phase, typically lasts 5 to 10 minutes. 

In this stage, our brain produces theta waves, which are slower and lower in frequency than the alpha and beta waves associated with wakefulness. 

This results in a relaxation of the mind and body. Muscle activity slows down, and conscious awareness of the external environment decreases. 

People awakened from this stage often feel like they have been daydreaming or drifting in and out of sleep.

2. Deeper sleep

Stage 2 marks the onset of proper sleep, as the individual becomes less aware of their surroundings. This stage constitutes about 40 to 60% of our total sleep. 

As you fall asleep, your brain produces rapid and rhythmic activity called sleep spindles, accompanied by a decreased body temperature and a slowing heart rate.

deeper sleep
Photograph: YuriArcursPeopleimages/Envato

3. Deep sleep

Deep or slow-wave sleep is the third stage, where the most vital processes occur. Here, the brain produces slower delta waves, making it harder to wake someone up. 

During this stage, the body repairs muscles and tissues, stimulates growth and development, boosts immune function, and stores energy for the next day.

4. Very deep sleep

This stage continues deep sleep, where the brain primarily produces delta waves. If someone is awakened during this stage, they often feel disoriented and dizzy for several minutes.

Stage 4 is crucial for the body as it continues the restorative processes initiated in Stage 3. Waking up during these stages results in sleep inertia – a state of cognitive impairment, groggy, and a desire to return to sleep.

5. REM sleep

The fifth and final stage, REM sleep, typically begins about 90 minutes after falling asleep. The brain activity revs up, closer to that seen in wakefulness. 

This stage is characterized by eye movement, increased respiration rate, and brainwave activity. 

It is often associated with intense dreaming due to increased brain activity, but it is also thought to contribute to memory consolidation, learning, and mood regulation. 

The amount of REM sleep we get increases with each successive sleep cycle throughout the night.

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REM sleep: Definition

Distinguished by rapid eye movements, this stage marks the culmination of a sleep cycle. But the ‘rapid eye movements’ are just one aspect of this multifaceted stage. 

The brain activity during this stage resembles wakefulness, despite the individual being sound asleep.

However, REM sleep is not just about active brain waves and fast eye movements. It’s a phase where major muscle groups experience temporary paralysis, a condition known as REM atonia [1]. 

This paralysis is believed to be a protective mechanism, preventing us from physically acting out our dreams.

On average, a person experiences about 4 to 5 REM sleep cycles per night, with each cycle lasting anywhere between 10 minutes to an hour. 

The first REM cycle of the night is typically the shortest, with each subsequent cycle lengthening and the final cycle possibly extending up to an hour.

What happens to the brain during REM sleep?

During this stage, the brain’s electrical activity significantly transforms [2]. Despite the individual being in a deep slumber, the brain activity closely resembles an awake state. 

Electroencephalogram (EEG) recordings show low-amplitude, high-frequency waves like those observed during wakefulness. This paradoxical state, where one’s brain is highly active in deep sleep, is one of the most fascinating aspects of this sleep stage.

Different brain regions play distinct roles during REM sleep, contributing to its complex phenomena.


Located in the brainstem, the pons sends signals to inhibit motor neurons, causing temporary paralysis during REM sleep, a condition known as REM atonia. 

This mechanism prevents us from physically acting out our dreams. Additionally, the pons is believed to be involved in regulating REM sleep itself.


The thalamus becomes highly active during REM sleep, acting as a relay station for sensory information.

It’s thought to play a crucial role in dream generation by transmitting images, sounds, and other sensory experiences from our memory to the cerebral cortex.


The amygdala, an almond-shaped set of neurons that process emotions, shows heightened activity during REM sleep. This may explain the emotional content often found in dreams.


Known for its critical role in memory formation and consolidation, the hippocampus is also active during REM sleep. 

Its activity is believed to be associated with dream recall and the integration of new memories with older ones.

Prefrontal cortex

Interestingly, the prefrontal cortex, involved in logic and decision-making, exhibits reduced activity during REM sleep, which might account for the often illogical and bizarre scenarios we experience in our dreams.

Overall, the intricate dance of neuronal activity during REM sleep reflects the complex processes in our brains as we dream and consolidate memories.

What physiological changes happen during REM sleep?

During REM sleep, our bodies undergo several observable physiological changes, while others are more subtle but equally significant.

1. Eye movements

Perhaps the most recognizable feature of REM sleep is the rapid movement of the eyes, from which the stage gets its name. 

These eye movements are believed to correspond to the visual images of our dreams, although the exact connection remains a topic of ongoing research.

2. Muscle atonia or paralysis

During REM sleep, major voluntary muscle groups experience temporary paralysis, known as REM atonia [3]. 

This protective mechanism prevents us from physically acting out our dreams, which could be dangerous.

3. Irregular heart rate and blood pressure

REM sleep are also characterized by variations in our cardiovascular system. Unlike the stable heart rate and blood pressure observed in non-REM stages, these parameters become irregular during REM sleep and may increase. 

These fluctuations are believed to result from the sympathetic nervous system’s heightened activity during this stage.

Irregular heart rate and blood pressure
Photograph: Pressmaster/Envato

4. Changes in breathing 

Our respiratory system also shows noticeable changes. Breathing during REM sleep becomes faster, irregular, and shallow. It’s thought that these respiratory changes might be linked to the vivid dream experiences during this stage.

5. Temperature regulation

During REM sleep, our bodies lose some ability to regulate internal temperature—a process termed “thermoregulatory desynchronization.” This could be why we sometimes feel hot or cold during vivid dreams.

These physiological changes underscore the significant differences between the REM sleep stage and other stages of sleep, pointing to the complex processes occurring as we slumber. 

Even though we may appear calm and peaceful while in REM sleep, our bodies are experiencing increased activity. This demonstrates the complex connection between our brains and the rest of our body.

REM sleep and dreaming

Although dreaming can occur in all stages of sleep, it’s most vivid and memorable during the REM phase.

The strong association between REM sleep and intense, narrative-driven dreaming is primarily due to the brain’s heightened activity during this stage, similar to wakefulness. 

The rapid eye movements for which REM sleep is named have also been suggested to coincide with the visual imagery of dreams, though this remains a topic of ongoing research.

Theories behind why we dream

Several theories have been proposed to explain why we dream, many focusing on REM sleep due to its association with vivid dreaming.

  • Cognitive process theory: This theory suggests that dreaming reflects our cognitive processes or thoughts. According to this theory, dreams are a way of reviewing and processing the day’s events.
  • Psychoanalytic theory: Proposed by Freud, this theory posits that dreams are a way of fulfilling unconscious desires or addressing unresolved issues.
  • Activation-Synthesis model: This neurological approach suggests that dreams are the brain’s way of making sense of random neural activity during REM sleep.
  • Memory consolidation theory: This theory argues that the primary function of dreams, especially during REM sleep, is to help with memory consolidation. Dreaming allows us to process and integrate new information with existing memories.

While none of these theories have been definitively proven, they contribute to our understanding of why we dream and REM sleep’s role in this fascinating cognitive process.

What’s the impact of REM sleep on learning and memory

Research suggests that REM sleep plays a significant role in learning and memory processes. The brain’s activity during REM sleep appears to help consolidate memories and enhance learning capabilities.

REM sleep and memory consolidation

Memory consolidation refers to stabilizing and strengthening memories after being acquired. 

REM sleep is thought to play a crucial role in this process. The heightened brain activity during REM sleep might help connect new information with existing memories, integrating them into long-term memory storage.

  • Procedural memory: REM sleep seems particularly important for procedural memory, which involves remembering how to do things (like riding a bike or playing a musical instrument). 

Studies have found that increased REM sleep after practicing a new skill can improve performance on the task [4].

  • Emotional memory: Research also suggests that REM sleep helps consolidate emotional memories. The amygdala, an area of the brain that processes emotions, is particularly active during REM sleep. 

This might help us process emotional experiences and integrate them into our memory in a healthier way.

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REM sleep and skill acquisition

Skill acquisition, or learning new skills, appears to be enhanced by REM sleep [5]. Some studies suggest that dreaming during REM sleep might contribute to this. 

For example, a musician might dream about a piece they are learning to play, or a language learner might dream in their target language. 

These dream rehearsals could help solidify the new skills, although the exact mechanisms remain unclear.

These findings underscore the importance of a good night’s sleep for learning and memory. 

It’s about getting enough sleep and progressing through the complete sleep cycle for adequate REM sleep.

Is REM sleep associated with longevity?

Sleep quality and duration are increasingly important factors in overall health and longevity. 

While all stages of sleep contribute to restorative processes, REM sleep has some unique impacts on lifespan.

REM sleep and physical health

Long-term REM sleep deprivation has been associated with several health issues, like obesity, diabetes, and cardiovascular disease, which can directly influence longevity. 

The disruptions in heart rate and respiration during REM sleep and potential changes in blood glucose levels and metabolism may contribute to these health outcomes.

REM sleep and physical health
Photograph: PolonioVideo/Envato

REM sleep and mental health

Adequate REM sleep is essential for maintaining good mental health. Chronic REM sleep deprivation has been linked to anxiety, depression, and other mental health disorders. 

Given the strong correlation between mental health and longevity, the role of REM sleep in promoting mental well-being may indirectly contribute to a longer lifespan.

REM sleep and cellular aging

Sleep, particularly REM sleep, may affect the body’s production of certain hormones and proteins involved in growth, stress response, and inflammation, all of which can influence the rate of cellular aging and, potentially, lifespan.

While the connection between REM sleep and longevity is complex and not fully understood, the evidence points to REM sleep being an essential component of a healthy, long life. 

As research in this area continues, we can expect to gain a deeper understanding of how REM sleep impacts our lifespan.

How does REM sleep influence mental health?

The impact of REM sleep on mental health is a burgeoning area of study in sleep research. A significant body of evidence suggests that the quality and quantity of REM sleep can profoundly affect our mental well-being [6].

Mood regulation

One of the key roles of REM sleep appears to be mood regulation. During REM sleep, our brains process emotional experiences, which may help us maintain emotional balance when awake. 

Lack of REM sleep or disturbances in REM sleep patterns has been associated with mood disorders such as depression and anxiety.


REM sleep might also help us cope with stress. Theories suggest that during REM sleep, we might replay stressful or traumatic events from the day without stress-related chemicals like norepinephrine. 

This could allow us to process these experiences safely and control them, helping us better handle such situations in the future.

PTSD and trauma

There’s also a compelling connection between REM sleep and post-traumatic stress disorder (PTSD). People with PTSD often experience nightmares and other disruptions in REM sleep.

Some treatments for PTSD focus on manipulating REM sleep to reduce nightmares and improve overall sleep quality.


This mental disorder is another condition linked with REM sleep anomalies. Studies have found that individuals with schizophrenia often have reduced or fragmented REM sleep, which might contribute to some of the cognitive symptoms of the disorder [7].

Types of REM sleep disorder

While REM sleep is crucial for our well-being, several sleep disorders specifically affect or are linked to this stage of sleep. 

Understanding these disorders is important for diagnosing and treating sleep-related issues.

1. REM Sleep Behavior Disorder (RBD)

This disorder is characterized by the loss of normal voluntary muscle atonia during REM sleep, leading to dreams-related physical activity. 

People with RBD might talk, yell, punch, kick, or leap out of bed during their sleep, sometimes leading to injuries.

2. Narcolepsy

This is a neurological disorder that affects the control of sleep and wakefulness. People with this condition often experience excessive daytime sleepiness and sudden sleep attacks. 

One of the hallmarks of narcolepsy is the direct transition from wakefulness into REM sleep, which can lead to symptoms like sleep paralysis and hallucinations.

3. Nightmares and nightmare disorder

While occasional nightmares are a shared experience, some people suffer from nightmare disorder, where nightmares become frequent and disruptive to sleep.

 This condition is more prevalent in children but can affect adults as well. It is often associated with post-traumatic stress disorder (PTSD).

4. Sleep paralysis

This condition involves a temporary inability to move or speak while falling asleep or upon waking. It happens when the brain transitions to or from REM sleep but is still somewhat aware of the surroundings. 

These episodes can last for a few seconds to a few minutes and can be frightening.

5. REM sleep deprivation

Though not a specific disorder, REM sleep deprivation can occur for various reasons, including certain medications, substance abuse, or lifestyle factors. 

Chronic REM sleep deprivation can lead to various physical and mental health issues.

Each disorder represents how REM sleep can be disrupted, leading to various potential health effects. 

It’s important to seek medical advice if you suspect you might have a sleep disorder, as effective treatments are available for many of these conditions.

How to improve REM Sleep

Improving the quality and quantity of your REM sleep can improve overall health and well-being. Here are some strategies to help enhance your REM sleep:

  1. Go to bed and wake up simultaneously daily to help regulate your body’s internal clock.
  2. Create a sleep-friendly environment.
  3. Try to turn off all screens at least an hour before bedtime to allow your body to prepare for sleep naturally.
  4. Limit your alcohol and caffeine intake, especially in the hours leading up to bedtime.
  5. Maintain regular physical activity but avoid intense exercise immediately before bedtime, as it may interfere with your ability to fall asleep.
  6. Manage stress levels through meditation, yoga, and deep breathing.
  7. If you have persistent trouble with sleep, seek advice from a healthcare professional to help identify any underlying issues and suggest appropriate treatments.

Closing thoughts

Our understanding of REM sleep has come a long way since it was first discovered in the 1950s, but there is still much to learn about this intriguing stage of our sleep cycle. 

Future research will continue to unravel the mysteries of REM sleep, providing deeper insights into this essential aspect of human life. 

However, disturbances in REM sleep can contribute to various mental and physical health problems, while healthy REM sleep can promote emotional stability and cognitive performance and potentially even increase lifespan

As such, prioritizing good sleep hygiene and ensuring adequate REM sleep is essential. The better we sleep, the better we can live, dream, and thrive.


What kind of sleep is best?

The “best” kind of sleep is balanced, consisting of all the necessary stages in the sleep cycle, including both non-REM and REM sleep. This should ideally be uninterrupted and around 7-9 hours per night. 

What causes a lack of deep sleep?

A lack of deep sleep, also known as slow-wave sleep, can be caused by several factors, including stress, aging, an uncomfortable sleep environment, alcohol and caffeine, which can disrupt the sleep cycle. Various medical conditions and sleep disorders, like sleep apnea and insomnia, can also interfere with deep sleep.

What is a normal sleep pattern?

A normal sleep pattern or sleep-wake cycle, typically includes four to six cycles of non-REM and REM sleep stages throughout a single night’s rest. Each cycle lasts about 90 to 110 minutes. 

What happens if I get too much deep sleep?

Excessive amounts of deep sleep can indicate an underlying health issue. For instance, a prolonged deep sleep phase can occur in certain sleep disorders, like hypersomnia, which leads to excessive sleepiness during the day despite long sleep durations at night.

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