Researchers have known about REM sleep since at least the 1950s. They managed to separate sleep into lighter and deeper stages, REM being the deepest. This stage is characterized by random and rapid eye movement, hence the name. It occupies around 20-25% of your total sleep architecture and is widely considered the most restorative and essential part of sleep. However, most of its functions remain a mystery to us. Over the years, theories have been suggested and scrutinized on what exactly happens during REM sleep other than the physiological symptoms we can detect, such as low muscle tone or an EEG pattern that resembles that of awake patients. We just cannot explain everything using our current technology. As a result, REM sleep is also known as “paradoxical sleep.” In this article, we will go over what is already known for a fact and showcase theories that have been proposed in recent years, in an attempt to bring across the proven and potential importance of uninterrupted, healthy sleep. By the end of this article, you will at the very least understand why longer, uninterrupted sleeping sessions are drastically healthier than the same amount of time spent sleeping, but in separate, smaller chunks. Let’s get into it.

REM Sleep – What We Know

While we aren’t aware of everything that goes on during REM sleep, we can detect certain events in our body that help us recognize this sleep stage. From these events, we can draw and document conclusions – and form various theories. Right now, we are going to focus on what we can prove and state as facts.

REM sleep is recognized by and named after rapid eye movement. Don’t be concerned about the name – the movement of your eyes in the REM sleep stage is less rapid than when you’re awake. The eyes follow PGO waves, and those waves originate in the brain stem. It is theorized that the PGO waves are involved in the eye movement of sleeping and wake animals (including us), and they appear right before we enter the REM sleep stage. At some point, we thought these eye movements were related to our sense of “vision” inside a dream since the REM stage is connected to vivid dreaming. However, even congenitally blind people (meaning those who are blind from birth) experience rapid eye movement.

Another way to recognize REM is through low muscle tone. To put it simply, your muscle movement is suppressed during this sleep stage, even though your brain activity is higher than during other sleep stages (which is why dreams can be more intense). Your face or fingers can still twitch, but the major voluntary muscle groups are relaxed. This paralysis is called REM atonia, and the lack of this phenomenon is sometimes called REM behavior disorder – a disorder that makes you act out your dreams.

Additionally, electroencephalography readings during the REM stage show fast, desynchronized, low amplitude neutral oscillation (brainwaves, in simpler terms). This is almost entirely opposite to how slow delta waves operate in NREM (non-REM) deep sleep. The theta rhythm in the hippocampus is equal to that of waking patients, with 40-60Hz gamma waves. On top of that, the electrical connectivity between different sections of the brain is not the same as that of a waking person. Among other things, this has been connected with how chaotic our dreams can be. As a whole, the brain tends to use up more energy during REM sleep than while the person is awake. NREM sleep energy usage is around 10-40% lower also.

While we’re in REM sleep, our blood and heart rate are considerably higher than in NREM sleep. Our breathing is closer to that of a waking person, and coughing is often suppressed. Body heat regulation is also suppressed during the REM stage, as we don’t sweat or shiver during it.

We spend most of the night in NREM sleep. The first REM cycle kicks in roughly 80 minutes after we fall asleep, and it initially doesn’t last very long – usually just a few minutes or less. However, as our sleep progresses, these cycles become longer and more frequent, with the longest one taking place right before we wake up. If you’re an adult, you can rely on around 90 minutes of REM sleep total, while babies can experience as much as 8 hours of REM sleep in one day. It’s assumed that this is because their cognitive abilities are still developing, and since the REM stage is crucial for mental repairs and growth, they need more of it.

Irregularities or interruptions in our REM sleep can lead to or indicate problems like REM rebound (the increasing frequency and regularity of rapid eye movement – usually occurring after a period of sleep deprivation or bad sleep quality), depression and a variety of other health issues.

REM VS Tonic Immobility

Have you ever seen a wilderness documentary where a rabbit or similar animal play dead? When they’re caught in a situation where they cannot run away (or fight), some animals will go completely rigid in order to avoid being detected or seriously injured by an attack. It has been observed in small birds or mammals, sharks, and lizards, among other creatures, and we call it tonic immobility, or the faint response. A theory suggests that REM sleep as a whole exists as an evolved version of this old defense mechanism. The sympathetic nervous system is more active during this sleep stage than when we’re awake – and this nervous system manages our “fight or flight” response.

Tonic immobility has been reproduced in controlled environments using electric shocks or mild stroking. This phenomenon has been used in stories of so-called “animal hypnosis,” where the tonic immobility response have been noted in smaller animals such as chickens. There have been claims that this response is also present with people undergoing severe trauma, although nothing conclusive has been proven.

Here is a list of similarities between REM sleep and tonic immobility, to help paint the picture:

–          In both states, your reflexes and muscle movement are suppressed. In a sleeping context, this is sometimes referred to as sleep paralysis.

–          Body heat regulation is changed during both of these states.

–          Notable eye movement, twitches, and jerking limbs are present in both REM sleep and during tonic immobility.

–          Both states have a relatively short duration in individual instances, going from just a couple of seconds to around 20 minutes (Note: REM sleep occurs more than once during the night).

–          The EEG pattern readings during REM sleep and tonic immobility are very similar. They feature additional theta waves, which are crucial for the patient’s memory and spatial awareness.

–          The biochemistry of the brain changes during both of these states. Serotonin and norepinephrine levels in the brain stem lower, while acetylcholine levels rise.

Tonic immobility is a last resort response to immediate and great danger. Its job is to help the body deal with and recover from serious trauma. Because of all the similarities in the list, we are led to believe that REM sleep is also meant to help us recover from stress or trauma through dreams. Additionally, some theorize that the dreams experienced in REM sleep serve as a sort of “virtual reality simulator” for the brain, where we mentally play out potentially threatening scenarios to figure out how to solve them or cope with them. The rapid eye movement that this sleep stage is named after could just be us trying to gather information within the dream, much like we would in a real dangerous scenario.

REM Helps Us Wake Up

The EEG readings of a person in REM sleep are very similar to those of an awake patient. On top of that, people who are woken up during REM sleep claim that their dreams were much more vivid than when they’re woken up during NREM. Researchers and scientists like W. R. Klemm propose a theory that REM assists the brain with waking up. The idea is that because the brain warms up during the REM stage, it acts as a sort of preparation process for waking up.

As Klemm explains in his study, a person goes through multiple REM cycles throughout the night. Each of those cycles represents the brain checking to see whether enough sleep had occurred. It partially explains why we have a REM cycle right before we wake up naturally. The brainstem arousal systems for REM and waking are very similar. It is therefore easy to conclude that REM sleep is a preparation for waking up. REM sleep is linked to mentally restorative and developmental processes, which explains why kids need more REM sleep than average (with babies spending roughly 50% of their sleeping time in REM stage).

Another hypothesis is that the REM stage lets different parts of the brain rest at different times, increasing our awareness while we sleep and making us more alert when we wake up. The idea is that this was an evolutionary benefit that kept early humans safe from various predators through increased alertness. When we swap from NREM to REM, a different part of the brain can have its “turn” being more active.

Thermoregulation Theory

To explain this theory, we need to look at homeostasis, specifically thermoregulation. A living organism needs a very specific combination of physical and chemical factors to metabolize properly. To maintain this ideal environment, we have evolved homeostatic mechanisms. Therefore, homeostasis is a dynamic balancing process through which our body maintains optimal conditions for every biological process we need. Thermoregulation is just another aspect of homeostasis and is how we maintain a steady body temperature even when the outside temperature is drastically different.

REM has been linked to warm-blooded animals, leading people to believe that it evolved parallel to thermal homeostasis. While we are in NREM sleep, our body and brain temperature drop. However, brain temperature rises considerably during REM sleep. While we’re in the REM stage, we can’t sweat or shiver, but our body finds alternative ways to regulate the temperature. Think of it as backup mechanisms for thermoregulation.

There’s a theory that our ancestors were nocturnal during ancient times, and that they slept during the day. NREM sleep primarily occurs in the earlier part of our sleep cycle, matching the daytime period of increased outside temperature (which is why our body cools down during that sleep stage). REM sleep occurs at the end of our sleep cycle, which corresponds to the twilight stage of that ancient cycle. During that time, the outside temperature was roughly equal to our regular temperature, so we didn’t need to shiver or sweat, and the need to contract our muscles was largely absent. This theory claims that the NREM and REM stages evolved out of how we slept back then.

The Protoconsciousness Theory

Have you ever had to rehearse a piece of dialogue? Or have you perhaps played pretend with your siblings as a child? The theory that REM sleep functions as the brain’s “VR simulator” likens this sleep stage to waking playtime in the way that we get to rehearse and act out hypothetical events in our mind. Playtime is incredibly vital for a young child as it helps them develop confidence, social skills, and interests, along with stimulating and improving their cognitive functions. REM sleep acts as a sort of mental repair mechanism, so it’s easy to see how this theory is plausible. Still, it has not been universally accepted as of yet, although more and more researchers are reaching similar conclusions and ideas in recent years.

Note: Even if this theory ends up being proven false, the positive effects of REM sleep on our memory retention and clarity the following day are obviously present.