REM Sleep


Written by Afy Okoye

Reviewed by Dr. Michael Breus

Our Editorial Process

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Rapid eye movement (REM) sleep is one of the two types of sleep. During this important period of rest, the body goes through distinctive changes that are associated with dreaming, the creation of long-term memories, learning, emotional processing, and brain development.

Though researchers are still learning about this active period of sleep, it’s clear that not getting enough REM sleep can negatively impact the body and mind. We cover the importance and function of REM sleep, along with the risks of not getting enough of this vital sleep stage.

Key Takeaways


    • Get enough REM sleep to help emotional processing and long-term memory creation.
    • Aim to get seven to nine hours of total sleep per night.
    • REM sleep may increase with certain health conditions or while taking some medications.

Understanding REM Sleep

Sleep is made up of several sleep stages that progress in a cyclical pattern throughout the night. The first three stages, which make up non-rapid eye movement (NREM) sleep, alternate with periods of REM sleep about every 90 to 120 minutes.

The body cycles through each stage of sleep around four to six times during the course of a night’s sleep. Each sleep stage is associated with characteristic changes in the brain and body.

  • NREM Stage 1: The first stage of NREM sleep is the transition from being awake to being asleep. In this stage, brain waves start to slow down.
  • NREM Stage 2: The second stage of NREM sleep is a state of light sleep. During this stage, brain activity is slowed but can have short bursts of activity.
  • NREM Stage 3: The third stage of NREM sleep is a deep sleep that is important for feeling rejuvenated in the morning. During this sleep stage, brain wave activity gets even slower, muscles relax, and it may become more difficult to be woken up.
  • REM Sleep: REM sleep is the final stage in the cycle. The first episode of REM sleep usually starts about 90 minutes after a person falls asleep. Brain wave activity, vital signs, and eye movement all increase during REM sleep.

During a typical night, about 18 to 23% of sleep time is spent in REM sleep. The first period of REM usually lasts around 10 minutes or less, but the amount of time spent in REM sleep usually increases as the night progresses. Later in the night, sleepers may spend around an hour at a time in REM sleep.

How Was REM Sleep Discovered?

REM sleep was first identified in 1953 after scientists observed that sleeping infants had phases of rapid-eye movements that alternated with less active periods of sleep. The notion of REM sleep was received with skepticism when it was initially proposed.

Over the following decades, scientific advances have allowed researchers to better study the activity within a sleeping brain. It’s now well established that REM sleep occurs not only in humans but also in many other animals, including mammals, birds, reptiles, and even cuttlefish.

What Happens During REM Sleep?

During REM sleep, a number of changes occur in the body and mind.

  • Eye Movements: The name “rapid eye movement” comes from the observation that a person’s eyes move rapidly from side to side during REM sleep.
  • Brain Activity: Brain activity during REM sleep is similar to what is seen while a person is awake. Some scientists refer to REM sleep as active or paradoxical sleep because brain activity is so similar to patterns during wakefulness.
  • Dreaming: Dreams can happen in any sleep stage, but are more likely to occur during REM sleep. Dreams in REM sleep may be longer as well as more emotional, vivid, and strange.
  • Elevated Vitals: During REM sleep, heart rate and blood pressure rise. Breathing can also become fast and irregular.
  • Paralyzed Movement: During REM sleep, many muscles in the body become paralyzed. Researchers believe that this temporary paralysis, called muscle atonia, keeps people from acting out what they dream.
  • Muscle Twitches: Even though skeletal muscles are immobilized during REM sleep, occasional muscle twitching still occurs. Emerging research suggests that the muscle twitches may activate certain brain regions and aid motor learning and development.
Part of what’s happening in REM sleep is that you move information from short-term memory to long-term memory.
Dr. Michael Breus

The Importance of REM Sleep

Sleep as a whole is important for health and overall functioning. Although researchers are still unraveling the many functions of REM sleep, studies suggest that REM sleep plays an important role in memory consolidation, emotional processing, and brain development.

  • Learning and Memory: REM sleep may have a critical role in forming memories and acquiring knowledge. One popular theory suggests that memories are sorted and retained or pruned during REM sleep.
  • Processing Emotions: REM sleep may also play a part in how people process emotions or remember emotionally charged events. Research suggests that REM sleep affects the level of emotion people attach to a memory.
  • Brain Development: REM sleep is likely important for brain development. Up to 50% of sleep is spent in REM sleep during early infancy. Later in life, REM sleep lasts longer after periods of learning.

How Much REM Sleep Do You Need?

The amount of time spent in REM sleep varies across life stages, with babies and children spending more time in REM sleep than adults. While infants may spend half of their sleep time in REM sleep, adults only spend around 18 to 23% of sleep in REM.

The time an adult spends in REM sleep varies from person to person. Adults generally need from 7 to 9 hours of sleep each night for optimal health. But so far, experts have not agreed on specific recommendations about the amount of REM sleep the average adult needs.

Scientists are still learning about how REM sleep is regulated and how much is required. However, it appears that REM sleep is controlled by groups of brain cells and functions homeostatically, which means that the body will naturally increase REM sleep when necessary.

What Happens if You Don't Get Enough REM Sleep?

Not getting enough REM sleep can have far-reaching effects. A variety of substances, medications and health conditions can impact the length and quality of REM sleep. Reducing the amount of REM sleep a person gets can affect their childhood development, learning, memory, and even pain tolerance.

Research suggests that being deprived of REM sleep interferes with implicit learning, a form of learning that occurs outside of a person’s awareness. Challenges in implicit learning can cause impairments in automatic tasks or activities that don’t require conscious recollection.

Losing REM sleep may also increase sensitivity to pain. One study showed that after being deprived of a full night’s REM sleep under laboratory conditions, people were able to tolerate pain for shorter times than people who were not REM-deprived.

About The Author

Afy Okoye

Staff Writer, Sleep Health

Afy is a writer and creative strategist in San Francisco with a master’s degree in international health policy from the London School of Economics. She has written for VeryWell Health,, and Paste magazine and edited peer-reviewed journal manuscripts for Elsevier. Afy says her work with The Sleep Doctor is anything but “sleepy.” She enjoys the opportunity to learn new information and share knowledge that gives people the power to make better choices. Afy also likes to read non-fiction, do creative writing, and travel solo.

  • POSITION: Side Sleeper
  • TEMPERATURE: Hot Sleeper

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