Exploring the Mystery of REM Sleep

Rapid Eye Movement (REM) sleep is one of the most known and talked about stages of sleep (there are five stages in total). It’s also by far the most mysterious.

The random eye movements that REM sleep is named after, the sleep paralysis, and other unique characteristics make this stage of sleep stand out to researchers.

Many studies have been conducted to try to get to the bottom of REM sleep, but somehow it seems that there are still more questions than answers when it comes to figuring out its purpose and functions.

Here’s a summary of what we know so far:

The Basics of REM Sleep

REM Sleep When It Occurs
The sequence of sleep stages during one night. Graphic courtesy of myDr

One of the earliest recorded observations of REM sleep was taken by Roman poet Lucretius in the first century B.C. He noticed that one of his hunting dogs was twitching in his sleep and wrote that it looked like the dog was chasing prey in his dream. However, it wasn’t until the 1950s that researchers discovered that sleep happens in different stages and became interested in the details of REM sleep.

We spend approximately 25%, or one quarter, of our night in REM sleep. The periods of REM sleep start out short and lengthen as the night progresses, with REM sleep coming in the cycle every 90 minutes. These REM stages can last anywhere from 10 minutes to an hour, and a third of the time spent in REM sleep involves rapid eye movements.

We know that during REM sleep we experience our most vivid dreams and that within those dreams, we often revisit significant parts of our day. One of the biggest hypotheses regarding REM sleep is that there’s a connection between REM sleep and memory, although researchers still disagree over whether this connection is true or false (more on that later).

What REM Sleep Does to Our Bodies

Most of us know that during REM sleep we dream and experience rapid eye movements. But are those eye movements the only physical change going on during REM sleep? Far from it! Research has shown that there is a LOT of physical stuff going on during REM sleep. The mysterious thing about it is that these physical changes are not always healthy, and it’s hard to pinpoint their exact functions.

For example, here are some of the physiological changes that take place during REM sleep:

  • Changes in autonomic nervous system functions
  • Rise in sympathetic nervous system activity
  • Cardiopulmonary changes
  • Lower oxygen levels
  • Impaired thermoregulation
  • Phasic eye movements and muscle twitching
  • Homeostatic deregulation
  • Muscle paralysis
  • High brain metabolic demand
  • Sexual activation

Logic tells us that all of these physical changes that take place during REM sleep MUST be serving some sort of evolutionary of physiological function, but that function remains unclear. In fact, some of these changes, such as cardiopulmonary changes and changes in breathing during REM sleep can be dangerous for vulnerable populations.

REM Sleep and Emotional Regulation/Memory Consolidation

As mentioned previously, many researchers believe in a link between REM sleep, emotional regulation, and memory. This was just a hypothesis until a few years ago, when a study was able to show a strong correlation between REM sleep and memory.

This study, conducted by Boyce et al. (2016), used optogenetics to turn off neurons associated with memory in mice during REM sleep. The next day, the mice couldn’t perform a spatial memory task learned the day before, compared to a control group who performed it successfully. The researchers also tried turning off these neurons outside of REM sleep but noticed no difference in memory.

Similarly, a study by Karni A. et al. (1994) found a connection between REM sleep and performance on a perceptual task in human trials. In their experiment, subjects improved on the skills learned the day before after having a regular night’s sleep. When REM sleep was disturbed, there were no performance improvements, and supressing non-REM sleep had no effect on performance.

This link shows how REM sleep plays a role in long-term memory and mastery. Have you noticed if you cram for a test all night without sleeping, when you get to class you’ve suddenly forgotten everything you’ve been studying? But when you break up your studying into blocks and sleep in-between, you absorb what you learned better and perform well on your test?

Creatives and successful people have learned to use this characteristic of sleep to their advantage. When you hit a roadblock on something you’re working on, getting a good night’s sleep can inspire you with the answers you need to solve your problem the next day. Many creatives keep a notebook beside their bed in case they have a breakthrough spurred by their dreams.

There’s also a link between quality of sleep and memory. Those who get daily aerobic exercise tend to sleep better and have more vivid dreams, whereas poor sleep quality is associated with dementia and Parkinson’s. Not getting enough sleep can contribute to memory loss or impairment in patients with these disorders, which is why it’s important to make sleep hygiene a priority upon diagnosis.

Despite these links, some scientists don’t believe that REM sleep is connected to emotional regulation or memory consolidation. According to Siegel, studies of people with repressed REM sleep due to drugs or brain damage show that these people don’t experience memory loss or impairment. He also notes that experiments where REM sleep is fully suppressed in animals show no changes in memory or learning.

REM Sleep and Neurodegenerative Disorders

To continue our discussion on REM sleep and memory, it’s important to look at the role of REM sleep in neurodegenerative disorders. One study conducted by Postuma et al. (2009), found that patients at a sleep disorder clinic who were diagnosed with REM Sleep Behavior Disorder (RBD) were at a higher risk for developing a neurodegenerative disease, particularly Lewy body dementia or Parkinson’s disease.

RBD is a disorder where REM sleep occurs without the usual muscle atonia, or sleep paralysis. These people may kick, punch, or cry out during sleep in association with vivid dreams experienced during REM sleep. In the study, patients’ risk of developing a neurodegenerative disease was 17.7% just 5 years after diagnosis of RBD, 40.6% at 10 years, and 52.4% at 12 years.

These researchers believed RBD may be related to a degeneration of sleep-related nuclei in the brainstem. Similar findings are shown in research by Arnulf, I. et al. (2000), in an exploratory study of patients with Parkinson’s who experience hallucinations and RBD. A postmortem study of one patient’s brain found Lewy bodies in the subcoeruleus nucleus, a part of the brain involved in REM sleep control.

More research into the relationship between REM sleep and neurodegenerative disorders is needed to improve patient treatment.

Is REM Sleep a Defense Mechanism?

Whether you believe that the purpose of REM sleep is memory consolidation and emotional regulation or not, there are other theories out there that are just as interesting. One of these theories was put forward by Ionnanis Tsoukalas, a researcher who believes that REM sleep may be connected to an ancient defense mechanism known as tonic immobility.

In a 2012 article published in the journal Dreaming, Tsoukalas points out that there are many commonalities between tonic immobility and REM sleep, including:

  • Sleep paralysis
  • Similar EEG patterns
  • Loss of muscle tone and suppressed reflexes
  • Length that varies between 5 seconds and 20 minutes
  • Eye movement/twitching
  • Similar changes in brain biochemistry
  • Body’s ability to regulate heat is compromised
  • Changes in breathing and heart rate

For those who aren’t familiar with the term, tonic immobility is when animals ‘play dead’ in emergency situations. Also called the ‘fight-flight-or faint response’ or animal hypnosis, tonic immobility is a last-resort reaction to extreme danger. From an evolutionary standpoint, this reflex is believed to help the body cope with traumatic situations.

During tonic immobility, chemicals in the brain such as acetylcholine are released which reduce pain and increase drowsiness. These same biochemical markers are present during REM sleep, which could suggest that dreaming and the REM state developed as a way to help the body deal with stress and trauma and recover during sleep.

Similarly, evolutionary psychologists believe that REM sleep and dreams are evidence for ‘threat rehearsal’ or ‘threat simulation theory’, whereby our dreams simulate real-life threatening situations. The function of dreams in this theory is rehearsing the different ways to deal with these threats, so we’re better prepared to deal with (or avoid) them when we’re awake.

What are the Consequences of REM Sleep Deprivation?

We all know that sleep deprivation can be challenging. Our bodies need sleep to work properly and for us to be at our best. Some of the less-than-ideal symptoms of sleep deprivation include fatigue, clumsiness, increased appetite, as well as put you at risk for more serious health problems. But what happens when we’re deprived specifically of REM sleep?

In a 2017 paper titled Dreamless: the silent epidemic of REM sleep loss, Rubin Naiman posits that modern society is causing an epidemic of sleep deprivation, and specifically REM sleep deprivation, that is contributing to snowballing health concerns affecting society today. As we know, many factors surrounding modern living can impact the quality and quantity of sleep we’re getting.

For example, trying to fit in work, family, and a social life can have people skipping sleep. Working overtime can too. Excessive exposure to artificial light or electronic devices (especially before bed) and reliance on alarm clocks to wake us up unnaturally also affect sleep. Using an alarm clock can wake us up in the middle of a REM sleep cycle, and we don’t know what exactly the implications of that might be.

Naiman notes that recreational substances including alcohol and cannabis can help people get to sleep but suppress or disturb REM sleep. Prescription drugs like sleeping pills and anti-depressants may contribute to less REM sleep and reduced sleep quality too. Some psychological disorders have been connected to irregular or dysregulated REM sleep, like depression.

Even though a lot of this information points to sleep loss and less restful sleep in general, Naiman believes that loss of REM sleep (and dreams) is important in and of itself.

He explains:

[su_quote]Dream eyes transcend waking egoic perspectives, opening us to greater social and spiritual consciousness and revealing a numinous world behind the world[/su_quote]

In this way, dreams serve an important purpose.

One thing we do know is that REM sleep loss increases the inflammatory response. Inflammation is responsible for a lot of the chronic illnesses that we experience as a society today. Getting proper sleep and doing our best to keep inflammation at bay is important for our health and wellbeing. REM sleep loss is also known to increase the risk of obesity and, as mentioned before, contributes to memory loss.

An interesting study by Roehrs T. et al. (2006) wanted to dig deeper into the relationship between sleep loss and acute/chronic pain. In human experiments, they found that subjects had increased sensitivity to pain. This sensitivity, referred to as hyperalgesia, was more significant for patients in the REM sleep loss group compared to the control group when reacting to radiant heat stimulus.

Why are these findings so significant? According to the research team:

[su_quote]These findings imply that pharmacologic treatments and clinical conditions that reduce sleep and REM sleep time may increase pain[/su_quote]

So, it’s possible that people who are on sleeping pills or anti-depressants that reduce REM sleep time may experience acute pain or worsened chronic pain, without realizing that sleep is a factor.


Even though there has been a fair amount of research done on the subject of REM sleep, it still remains a bit of a mystery. If sleep and dreaming is supposed to be restorative, why do we experience potentially dangerous physiological changes during REM sleep? Does REM sleep help with memory and emotions, act as a defense mechanism, or something else?

Despite this research and speculation, it’s possible that the true function of REM sleep remains unknown.