What Is REM Sleep?

Rapid eye movement (REM) sleep is one of the four stages the brain goes through during the sleep cycle. It is marked by several physiological changes, including muscle relaxation, eye movement, faster respiration, and increased brain activity.

This period of the sleep cycle usually takes place about 90 minutes after a person first falls asleep. Each REM sleep cycle typically occurs every 90 to 120 minutes. People spend approximately 25% of their total time asleep in REM sleep.

Sleep needs vary by age, but the Centers for Disease Control and Prevention (CDC) suggests that adults need around seven to eight hours of sleep each night. Since REM sleep accounts for about a quarter of your total sleep, you should spend around 120 minutes in REM sleep each night.

This article discusses the signs and effects of REM sleep. It also explores some steps you can take to improve your REM sleep.

Signs of REM Sleep

The brain and body go through a number of changes that are characteristic of this stage of sleep. Some key signs of REM sleep include:

• Body temperature changes
• Body twitching, particularly in the face, arms, and legs
• Increased blood pressure
• Increased brain activity that is similar to awake states
• Increased heart rate
• Increased oxygen use by the brain
• Rapid eye movements
• Rapid, irregular breathing
• Sexual arousal

Most people also experience a state of temporary paralysis known as atonia. During REM sleep, the muscles that prevent body movements become active, leading to temporary paralysis. This is a normal function of REM sleep and prevents you from physically acting out dreams.

REM Sleep vs. NREM Sleep

REM sleep is distinguishable from NREM sleep by the different brain wave patterns and eye movements that characterize each type of sleep. REM sleep is marked by the suspension of homeostasis, rapid eye movements, and increased brain activity. NREM sleep includes three distinct stages characterized by gradually slowed brain waves.

There are also important physiological differences between REM and NREM sleep. REM sleep is initiated by the secretion of acetylcholine and the inhibited production of serotonin and other monoamines

When Does REM Sleep Happen?

There are four different stages of sleep. NREM sleep accounts for the first three stages, and REM sleep is considered the fourth stage.

• Stage 1: This is the first stage of NREM sleep that involves the process of falling asleep. The body becomes more relaxed during this period of sleep, and brain activity begins to slow. This stage is very brief, lasting around five minutes.
• Stage 2: During this stage of sleep, body activity and brain waves slow. People spend about half of their time sleeping in stage 2 sleep. This stage typically lasts between 10 and 60 minutes.
• Stage 3: Also known as deep sleep, this stage involves slower body activity and brain waves. This period of sleep is important for memory and learning. Stage 3 usually lasts 20 and 40 minutes.
• Stage 4: This is REM sleep, when body and brain activity increase, rapid eye movements begin, and dreaming occurs.
  

It is important to note that these stages do not follow a perfectly sequential pattern as you sleep. During the first sequence, stages 1, 2, and 3 occur, and then stage 2 begins again. It is after this second occurrence of stage 2 sleep that REM sleep first appears.

A complete sleep cycle takes roughly 100 minutes to complete. Four to five cycles may occur each night, depending on how long a person sleeps.

Impact of REM Sleep

REM sleep plays an important role in brain development as well as other functions including mood, dreaming, and memory.

Dreams

Dreams happen during the rapid eye movement (REM) stage of sleep. In a typical night, you dream for a total of two hours, broken up by the sleep cycle.

Researchers do not fully understand the exact reasons why we sleep. They do know that newborns dream and that depriving rats of REM sleep greatly shortens their lives. Other mammals and birds also have REM sleep stages, but cold-blooded animals such as turtles, lizards, and fish do not.

Brain Development

Research suggests that REM sleep serves an important role in the development of the central nervous system (CNS) during infancy. The high activity levels in the brain during this stage of sleep may play a role in developing and strengthening neural connections. 

Memory

Dreams may be one way that the brain consolidates memories. The dream time could be a period when the brain can reorganize and review the day’s events and connect new experiences to older ones. Because the body is shut down, the brain can do this without additional input coming in or risking the body “acting out” the day’s memories.

Some researchers believe that dreams are more like a background “noise” that is interpreted and organized. This activation-synthesis theory suggests that dreams are merely the brain’s attempt to make sense of random signals occurring during sleep.

Emotional Processing

REM sleep is also believed to play an important part in emotional processing. Dreaming may be a part of this process. Research suggests that lack of sleep contributes to decreased emotional memory consolidation and poor encoding of emotional memory.

Effects of a Lack of REM Sleep

REM sleep plays an important role in a number of functions, including learning and memory. Interruptions to REM sleep can sometimes result in problems. As a result, the lack of REM sleep is linked to several health concerns, including the following.

Increased Weight

Reduced REM sleep is associated with changes in leptin levels and may be associated with increased appetite and weight.

Memory Consolidation

The pons also sends signals to cerebral cortex by way of the thalamus (which is a filter and relay for sensory information and motor control functions deep in the brain). The cerebral cortex is the part of the brain involved with processing information (learning, thinking, and organizing).

The areas of the brain that are “turned on” during REM sleep seem to help learning and memory. Infants spend almost 50% of their sleep time in REM sleep (compared to 20% for adults), which may be explained by the tremendous amount of learning in infancy.

Movement

REM sleep usually begins after a period of deep sleep known as stage 3 sleep. An area of the brain called the pons—where REM sleep signals originate—shuts off signals to the spinal cord. That causes the body to be immobile during REM sleep.

When the pons doesn't shut down the spinal cord's signals, people will act out their dreams. This can be dangerous because acting out dreams without input from the senses can lead to accidents and physical harm such as running into walls and falling down stairs. This condition is rare and different from more common sleepwalking and known as REM sleep behavior disorder.

Sleep Disorders That Affect REM Sleep

There are a number of different sleep disorders that can cause problems with REM sleep. These include:

• REM sleep behavior disorder (RBD): People who have this condition may not experience muscle paralysis during REM sleep, which can lead to acting out dreams, resulting in disrupted sleep and injury.
• Nightmare disorder: People with this condition experience intense, terrifying nightmares during REM sleep. This leads to disrupted sleep and considerable distress.
• Narcolepsy: This condition involves having episodes where a person suddenly goes from wakefulness to REM sleep. 
• Sleep apnea: People with this condition experience brief lapses in breathing that lead to repeated waking. While this does not specifically affect REM sleep, it does contribute to worse sleep quality and duration.

How to Improve REM Sleep

There are things that you can do to make the most of your REM sleep each night.

Follow a Sleep Schedule

Go to bed at the same time each night and wake at the same time each morning. Following a sleep schedule can help maximize the amount of quality sleep, including REM sleep, that you get each night.

Watch Your Alcohol Intake

Keep your alcohol intake light before going to bed. Research has found that even moderate alcohol intake in the evening can interfere with REM sleep. Light alcohol intake doesn't seem to have the same impact, but moderate to heavy consumption delayed the onset of REM sleep and led to fewer REM sleep phases during the night.

Remember Your Dreams

You can develop your ability to remember your dreams by keeping a journal near your bed and writing down everything you can about your dreams when you first wake up. After a few weeks, your ability to remember your dreams will improve.

Some people claim that they have lucid dreams, which are dreams in which they can participate and change the dream as it develops. Lucid dreaming can be triggered through a number of techniques, though little research has been done on it.