REM Sleep: What Is Rapid Eye Movement Sleep?
Quick Summary
Rapid Eye Movement (REM) sleep is a unique stage where your brain is as active as when you're awake, but your body's major muscles are temporarily paralyzed. This state is essential for processing emotions and strengthening certain types of memories.
The temporary paralysis during REM sleep, called atonia, is a protective mechanism that prevents you from physically acting out your often vivid and emotional dreams.
A serious condition called REM Sleep Behavior Disorder (RBD) involves the failure of REM sleep paralysis, causing people to act out their dreams. RBD is a strong early predictor of brain conditions like Parkinson's disease in some populations.
Disruptions in REM sleep are linked to significant health issues, including insomnia, depression, and post-traumatic stress disorder (PTSD).
Ever woken up from a dream so vivid it felt real? You were likely in the middle of Rapid Eye Movement (REM) sleep, a period of the night that is as critical as it is strange. REM sleep is a state defined by a contradiction: your brain is alive with activity, much like it is during the day, yet your body is almost completely still.
So what’s going on during REM sleep and why are dreams so unusual during REM sleep?
What Is Rapid Eye Movement (REM) Sleep?
Rapid Eye Movement (REM) sleep is a distinct stage of sleep that involves an electrically active brain, rapid eye movements, and a near-total paralysis of the body's skeletal muscles. First identified by researchers Aserinsky and Kleitman in 1953, the discovery of REM sleep changed our understanding of sleep, revealing it to be an active and complicated process rather than a simple period of rest (Aserinsky & Kleitman, 1953).
Is REM Sleep The Same As “Paradoxical Sleep”?
The REM sleep stage is often called "paradoxical sleep" because it's a puzzle: brain scans show activity patterns that look very similar to those of someone who is fully awake and alert, yet the body is almost completely still (Siegel, 2020).
How Much Of A Night’s Sleep Is REM Sleep?
For a healthy young adult, REM sleep makes up about 20-25% of the total time spent asleep. But REM sleep doesn't happen right away; you typically enter your first REM period about 80 to 100 minutes after falling asleep, after cycling through the other stages of sleep.
These REM periods then repeat roughly every 90 minutes, becoming longer and more intense in the final hours of the night (Keenan & Hirshkowitz, 2022).
But what exactly is happening inside the brain and body to create this unusual state?
What Does the Brain Do During REM Sleep?
During REM sleep, the brain goes through a major shift in activity, which can be observed using polysomnography, a comprehensive test used to diagnose sleep disorders. This activity has two main types of features: those that are continuous and those that happen in short bursts.
The most important continuous feature is the brain's electrical activity. An electroencephalogram (EEG), which measures brainwaves, shows a low-voltage, high-frequency pattern that looks almost identical to the EEG of an awake, active brain (Siegel, 2020). This is very different from the slow, powerful brainwaves seen in deep, non-REM sleep.
At the same time, the brain sends signals that cause a deep loss of muscle tone, a state of temporary paralysis known as atonia. This temporary paralysis is a critical protective measure. It is actively created by the brainstem, which sends signals down the spinal cord to quiet the nerve cells that control your muscles (Chase & Morales, 2000). This ensures you don't physically act out the vivid, and sometimes aggressive, dreams that are common in this stage.
The short bursts of activity that give REM sleep its name include:
Rapid Eye Movements: The characteristic flurries of quick, jerky eye movements that occur behind closed eyelids. These movements are closely linked to the visual imagery of dreams (Dement & Kleitman, 1957).
Muscle Twitches: Despite the general paralysis, small muscle twitches in the face, fingers, and toes can break through.
Irregular Body Functions: Your body's automatic functions become irregular. Heart rate, blood pressure, and breathing can speed up and become variable, reflecting the intense brain activity (Hanlon et al., 2022).
How Does the Brain Control the Switch into REM Sleep?
The brain controls the switch into REM sleep using a complex network of neurons (nerve cells) located deep within the brainstem, an area connecting the brain to the spinal cord. This system works like a biological flip-flop switch, with specific groups of neurons turning REM sleep "on" while others turn it "off" (Siegel, 2020).
The "REM-on" system is driven primarily by neurons that use the neurotransmitter acetylcholine, a chemical messenger in the brain. These cells, located in an area of the brainstem called the pons, become highly active to promote the alert brainwaves and other features of REM sleep (Brown et al., 2012). Another group of neurons that produce melanin-concentrating hormone (MCH) also helps start and lengthen REM periods (Komagata et al., 2019).
For REM sleep to begin, the "REM-off" system must be silenced. This system is made up of nerve cells that release chemical messengers called monoamines, including norepinephrine and serotonin.
During wakefulness, these neurons are active and keep you alert while suppressing REM sleep. As you transition into REM, these monoamine neurons fall silent.
This drop in activity is essential; it releases the "brake" on the REM-on neurons, allowing the REM state to begin (Siegel & Rogawski, 1988). This shutdown of norepinephrine is also what allows the pathways responsible for muscle atonia to become active, ensuring the body remains still.
Why Is the Brain So Active and Emotional During REM Sleep?
The brain is so active during REM sleep because it is busy with intense internal work related to emotion and memory. Brain scan studies, which measure blood flow and energy use, show that the brain's overall energy use, or metabolic rate, during REM sleep is as high as, or even higher than, during quiet wakefulness (Braun et al., 1997).
Why Are REM Sleep Dreams So Bizarre?
During REM sleep, activity is not the same everywhere in the brain. Certain areas become supercharged while others quiet down:
Activation of the Brain's Emotional Center: The most significant increases in activity occur in the limbic system, the brain's emotional core. Areas like the amygdala, which is central to processing fear and other strong emotions, and the hippocampus, which is involved in memory, become highly active (Maquet et al., 1996). This intense activation is believed to be the reason why dreams during REM sleep are often so vivid, bizarre, and emotionally charged (Schwartz & Perogamvros, 2020).
Quieting of the Brain's Logic Center: In contrast, parts of the dorsolateral prefrontal cortex, the brain region responsible for logical reasoning, critical thinking, and self-awareness, become much less active (Maquet et al., 2000). This may explain many of the strange characteristics of dreams, such as our lack of insight (not realizing we are dreaming), jumbled timelines, and acceptance of bizarre scenarios without question (Schwartz et al., 2005).
This unique pattern of brain activity suggests that REM sleep provides a special environment for the brain to work through emotional experiences without the filter of logic.
But what purpose do these strange dreams serve?
What Is the Function of REM Sleep and Dreaming?
The primary functions of REM sleep and dreaming appear to be focused on managing emotions and strengthening memories. While you sleep, your brain isn't just resting; it's actively working to process the day's events, helping you learn and prepare for the future.
One leading theory is that REM sleep helps to "reset" or "readjust" our emotional circuits. By reactivating emotional memories in a brain state where norepinephrine - a chemical associated with stress - is absent, REM sleep may strip away the sharp, painful edge from difficult experiences (Tempesta et al., 2018). It allows the brain to process the memory and its meaning without re-experiencing the full emotional intensity, a process sometimes described as "sleep to forget the emotion, but remember the event." (Tempesta et al., 2018).
REM sleep is also critical for strengthening certain types of memories. While deep sleep is important for locking in facts and events, REM sleep seems to be particularly important for:
Skill Memory: Skills and habits, like learning to play a musical instrument or ride a bike, are strengthened during REM sleep (Li et al., 2017).
Creative Problem-Solving: The unique chemical environment of REM sleep may allow the brain to make new and creative connections between different ideas. This can lead to creative insights and solutions to problems that seemed unsolvable during the day (Cai et al., 2009).
What Happens When REM Sleep Is Disrupted?
When the carefully balanced processes of REM sleep break down, it can have serious consequences for both mental and physical health. Problems can range from a general instability of the REM state to a complete failure of its core components, leading to a group of conditions known as REM parasomnias.
Many common health problems are linked to poorly regulated REM sleep. The stability of this sleep stage can be a powerful indicator of underlying stress, mental health conditions, and even future neurological disease.
How Does Unstable REM Sleep Contribute to Insomnia?
In people with chronic insomnia, REM sleep is often described as being "restless" or unstable. This is particularly true for a severe subtype of the disorder known as Insomnia with Objective Short Sleep Duration, where individuals are in a state of 24-hour hyperarousal, or a persistent state of high alert (Vgontzas et al., 2013).
This hyperarousal state prevents the brain from fully settling into a restorative sleep pattern, and it disrupts the emotional processing functions of REM sleep. One study found that restless REM sleep prevented the amygdala from properly resetting overnight, meaning the brain's fear center remained overly sensitive (Wassing et al., 2019). Instead of helping to resolve emotional distress, this unstable REM sleep can keep a cycle of anxiety and worried thinking going, making it harder to fall asleep and stay asleep on subsequent nights (Riemann et al., 2012).
How Does Sleep Apnea Affect REM Sleep?
For individuals with obstructive sleep apnea (OSA), REM sleep is a particularly risky time. The deep muscle paralysis, or atonia, that is essential for keeping you still during dreams also relaxes the muscles that hold your upper airway open. As these muscles relax, the airway is much more likely to collapse.
This often leads to more frequent, severe, and prolonged breathing interruptions, known as obstructive events, specifically during REM sleep. These repeated events severely fragment the REM stage, preventing the brain from sustaining this restorative process.
This fragmentation has serious consequences, driving spikes in the body's 'fight-or-flight' response that increase blood pressure and strain the cardiovascular system. It also harms thinking abilities that rely on intact REM sleep; for instance, one study demonstrated that when breathing events disrupted REM, participants had significantly more trouble with spatial memory tasks the following day (Varga et al., 2014).
What Is the Link Between REM Sleep and Psychiatric Conditions?
Disruptions in REM sleep are a key feature of several major psychiatric disorders, reflecting underlying issues with emotional regulation.
Major Depressive Disorder (MDD): Depression is strongly associated with a pattern of REM sleep "disinhibition." This means people with depression often enter their first REM period much faster than normal (a shortened REM latency) and may spend more total time in REM sleep (Kupfer, 1976). This is thought to reflect an imbalance in the brain's chemical messengers that control the sleep-wake cycle.
Post-Traumatic Stress Disorder (PTSD): In contrast to depression, PTSD is characterized by highly fragmented REM sleep. The brain's adrenergic system, which produces adrenaline, becomes overactive, causing frequent awakenings from REM sleep (Hanlon et al., 2022). This constant disruption prevents REM sleep from performing its function of processing traumatic memories, trapping the individual in a cycle of repeated distress.
What Is REM Sleep Behavior Disorder (RBD)?
REM Sleep Behavior Disorder (RBD) is a serious sleep disorder in which the normal muscle paralysis of REM sleep fails. This condition, known as REM sleep without atonia, causes individuals to physically act out their dreams, which are often vivid, action-packed, and violent (Schenck et al., 1987).
A person with RBD might shout, punch, kick, or leap out of bed while dreaming they are defending themselves from an attacker. These actions can cause serious injury to the individual or their bed partner.
The most critical aspect of RBD is its powerful connection to a group of brain diseases called synucleinopathies, which get worse over time. These include Parkinson's disease, Dementia with Lewy Bodies, and Multiple System Atrophy.
The onset of RBD can appear years or even decades before the motor and cognitive symptoms of these diseases, making it one of the strongest known early predictors for their development (Dauvilliers et al., 2018).
What Are Other REM-Related Sleep Disorders?
Besides RBD, other conditions involve the separation of the different parts of REM sleep:
Nightmare Disorder: This is defined by recurrent, intensely disturbing dreams that cause awakenings and significant distress. These nightmares arise almost exclusively from REM sleep (Gieselmann et al., 2019).
Recurrent Isolated Sleep Paralysis: This involves a temporary inability to move or speak either when falling asleep or waking up. It occurs when the muscle atonia of REM sleep intrudes into wakefulness, which can be a terrifying experience, often accompanied by hallucinations.
Narcolepsy: This neurological disorder is fundamentally a problem with the brain's ability to control the lines between sleep and wakefulness. It is caused by the loss of neurons that produce hypocretin (orexin), a key chemical for maintaining alertness. Symptoms like cataplexy, a sudden loss of muscle tone triggered by strong emotions, represent the intrusion of REM atonia into the waking state (Siegel, 2020).
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Frequently Asked Questions: REM Sleep
Q1: What is REM sleep and why is it important?
A1: Rapid Eye Movement (REM) sleep is a unique stage of sleep where your brain is highly active, similar to when you are awake, but your body's major muscles are temporarily paralyzed (Aserinsky & Kleitman, 1953). This stage is important for several key functions, including managing emotions, strengthening memories for skills, and creative problem-solving. By processing emotional experiences, REM sleep helps "reset" the brain's emotional circuits, which can soften the impact of difficult events (Tempesta et al., 2018).
Q2: Why are your muscles paralyzed during REM sleep?
A2: Your muscles are paralyzed during REM sleep as a protective measure to prevent you from physically acting out your dreams. This state, called atonia, is actively created by your brainstem, which sends signals to quiet the nerve cells that control your muscles (Chase & Morales, 2000). This paralysis ensures you remain still and safe, even when your dreams are vivid or action-packed.
Q3: What happens if you don't get enough REM sleep?
A3: Not getting enough REM sleep can have serious consequences for both mental and physical health. Disruptions to REM sleep are linked to insomnia, as a state of hyperarousal can lead to "restless" REM that fails to resolve emotional distress (Riemann et al., 2012). It is also a key feature in psychiatric conditions like depression and PTSD, where it can reflect an imbalance in the brain's chemical messengers and an inability to process traumatic memories (Kupfer, 1976; Hanlon et al., 2022).
Q4: What is REM Sleep Behavior Disorder (RBD)?
A4: REM Sleep Behavior Disorder (RBD) is a serious sleep disorder where the normal muscle paralysis during REM sleep fails. This causes individuals to physically act out their dreams, which can involve shouting, punching, and kicking (Schenck et al., 1987). RBD is significant because it is a strong early predictor of neurodegenerative diseases like Parkinson's disease, often appearing years or decades before other symptoms develop (Dauvilliers et al., 2018).
Q5: What is sleep paralysis?
A5: Sleep paralysis is a temporary inability to move or speak that occurs when you are falling asleep or waking up. It happens when the muscle atonia that is normal during REM sleep intrudes into a state of wakefulness. While it can be a frightening experience, especially since it is sometimes accompanied by hallucinations, it is a recognized REM-related sleep disorder.
Q6: How can I get better quality REM sleep?
A6: While you can't directly control your sleep stages, you can adopt habits that promote a healthy, high quality sleep. The best strategies include maintaining a consistent sleep schedule by going to bed when sleepy and waking up at the same time daily, even on weekends. It is also helpful to avoid alcohol before bed, as it can suppress and fragment REM sleep. Finally, managing stress and creating a cool, dark, and quiet bedroom can help support your body's natural sleep processes (Bach et al., 2002).
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Written By The Better Sleep Clinic
Reviewed By Dan Ford, Sleep Psychologist
