REM Sleep: There’s More Behind “Shut-Eye” Than You May Think

REM sleep
The stages of sleep, including REM sleep, are important to our physical and mental health.

For a long time, people thought that sleep was just a dormant state, or just something we had to do to get on with our daily lives. We now know that sleep is a lot more complicated than a passive state, and researchers have shown that sleep has stages that cycle throughout the night. All of them, especially REM sleep, are essential for our health and functioning. And we also know that our brains are actually very active during all stages of sleep, and different things happen during different sleep stages. If you couldn’t tell from your own experience, how much sleep we get, as well as the quality of sleep is definitely important.

Stages of Sleep

On average, including all sleep stages, a complete sleep cycle takes 90 to 110 minutes, with the first REM sleep period usually occurring about 70 to 90 minutes after falling asleep. At first, sleep cycles contain relatively short REM periods and long periods of deep sleep. Then throughout the night, REM sleep periods increase in length and the amount of deep sleep decreases. By the time you wake up, you will spend nearly all of your sleep time in stages 1, 2, and REM. Some phases are necessary to help you feel rested and have the energy to get through the next day. Other phases help you learn and form memories. Each sleep stage in any sleep cycle fulfills a physiological and neurological function, each of which is necessary for your body. So, if your sleep cycle is interrupted or if any stages are missing, some functions are not fully executed, and you may feel tired even after you think you got enough sleep. This is known as “sleep inertia”. If your REM sleep is disrupted, you won’t follow the normal sleep cycle the next time you fall asleep. Instead, you will go directly into REM sleep and have extended periods of REM until you “catch up” on this stage of sleep.

Since 1968, the widely accepted standard for sleep cycles went according to the Manual of Sleep Classification by Rechtschaffen and Kales. In this guide, there are four distinct stages, or phases, of sleep:

Sleep stage 1:

Stage 1 is when you are just between feeling awake and asleep, possibly lightly sleeping, and can be awakened again very easily.

Sleep stage 2:

Stage 2 is a deeper sleep but is still considered to be a fairly light sleep. At this stage, the body temperature lowers slightly, eye movements stop, and our brain waves slow down, and there are occasional bursts of rapid brain waves called sleep spindles.

Sleep stages 3 and 4:

Stages 3 and 4 (or N3) are considered to be our deep sleep stages. Stage 3 is the transitional period between light and deep sleep, and when you don’t experience any eye movement or muscle activity. Your brain also starts producing delta waves, which are extremely slow brain waves, interspersed with smaller, faster waves. Stage 4 is when your brain produces almost exclusively delta waves. Stages 3 and 4 are most restorative to the brain and body. It is when you are least able to be awakened, your muscles relax and grow, and are repaired by an increased supply of blood. Your body releases needed hormones work to boost immune function and builds up energy for the next day. People who are awakened during their deep sleep stages are not able to transition to a fully awake state immediately and often feel groggy and disoriented after they wake up. Deep sleep is when some people experience night terrors or sleepwalking, or when children wet the bed.

Non-REM sleep

Stages 1-4 are combined into what is known as NREM, or non-REM sleep. NREM sleep accounts for about 75% of the entire sleep cycle, and REM sleep makes up about 25% of the cycle. The stages start at stages 1-4, and then into REM sleep. The American Academy of Sleep Medicine (AASM) established a new system in 2007 which combined stages 3 and 4 into a single stage, referred to now as N3. Stages 1 and 2 were renamed N1 and N2, respectively. So, the AASM stages are: N1, N2, N3, and REM sleep is referred to as R.

REM Sleep

A REM sleep stage can last up to an hour. As your sleep cycles repeat, you will enter REM sleep several times during the night.

Your body is in REM sleep:

  • breathing becomes irregular, more rapid and shallow
  • limb muscles will become very relaxed, even paralyzed and unresponsive
  • rapid and random side-to-side movements of the closed eyes. These eye movements can be monitored and measured by a technique called electrooculography (EOG).
  • heart rate increases
  • blood pressure rises
  • males can develop penile erections
  • body temperature is not as tightly regulated so you might be awakened by irregular hot or cold temperatures.

The REM sleep stage is thought to be involved in the process of storing long-term memories, especially procedural and spatial memory, and learning. However, the exact mechanisms are not completely understood, and the learning may not be at the same extent as during deep sleep cycles. Some studies have shown that when people are deprived of REM sleep, they are unable to remember things that they were taught before going to sleep. Brain waves during REM sleep look very similar to how brain waves look during a wakeful state. It’s also been shown that a lack of REM sleep has been linked to certain health conditions, including migraines (See more about migraine triggers).

Studies have shown that animals also dream during their REM sleep stages.
Studies have shown that animals also dream during their REM sleep stages.

There are so many signals being sent to the cortex in the brain during REM sleep, but not all of them are for the purpose of learning. Some of the “random” signals that may form the basis for a story that the brain tries to interpret or find meaning in, which causes dreaming. We typically spend more than 2 hours each night dreaming, with the majority of dreams occurring during REM sleep. It is thought that the temporary paralysis that accompanies REM sleep is an inherent measure to protect us from injuries which could occur if we try to physically act out vivid REM dreams. Lucid dreaming is a dream state in which the person is completely aware that they are dreaming. 

REM Sleep Disorders

During REM sleep, signals are sent to the spinal cord to shut off movement, causing a temporary paralysis of the arms and legs. Abnormal disruption of this temporary paralysis can cause people to move while they are dreaming and trying to act out those dreams, and cause potential injury. This is called REM sleep behavior disorder. Despite being supposed to be paralyzed, people can move and walk around, or talk, scream or shout in their sleep. Some people may even hit or punch their partner in their sleep. Benzodiazapines can work to eliminate the disorder about 90% of the time. In other cases, antidepressants or melatonin may reduce violent behavior. However, you should also make the bedroom a safe environment, and remove any sharp or breakable objects.

A lack of REM sleep can impair the ability to learn complex tasks. This suggests that REM sleep is a vital component of our sleep patterns, particularly during early childhood development. Other sleep disorders usually involve less than adequate sleep that interferes with normal physical, mental and emotional functioning. Excessive sleep can also be a problem, such as a narcolepsy, or hypersomnia.

Depression is often accompanied by insomnia, or sometimes the opposite, hypersomnia. Those suffering from depression tend to experience REM sleep much earlier in their sleep cycles than normal, which suggests a disruption in the drive-regulation function. Since some antidepressants (are antidepressants for you?) deprive the patient of REM sleep, this may fix the abnormality. Since depression shares many risk factors and biological features with various sleep disorders, misdiagnosis is common. It’s important to get help if you are suffering from either depression or sleep disorders. 


American Academy of Sleep Medicine. International Classification of Sleep Disorders (Third Edition. Darien, IL: American Academy of Sleep Medicine, 2014.

Boeve, B. (2010) REM sleep behavior disorder: updated review of the core features, the RBD-neurodegenerative disease association, evolving concepts, controversies, and future directions. Annals of the New York Academy of Sciences;1184:15-54.

National Institute of Neurological Disorders and Stroke, National Institutes of Health. Brain Basics: Understanding Sleep. Retrieved on April 5, 2017 from Understanding Sleep Cycles: What Happens While You Sleep. Retrieved on April 6, 2017 from

Stickgold, Robert (2009). The Neuroscience of Sleep. Amsterdam: Boston : Academic Press/Elsevier. pp. 61–86.

Tsoukalas, I. (2012). The origin of REM sleep: A hypothesis. Dreaming. 22 (4); 253–283.

Walcutt, D. (2016). Stages of Sleep. Psych Central. Retrieved on April 6, 2017, from

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