What Happens During REM Sleep

What Happens During REM Sleep?

If you know just a little about REM sleep, you’ll know it’s the sleep that is most associated with dreaming. And you might wonder just what is going on that is causing you to have such vivid and illogical dreams?

I wondered the same thing so I spent a few hours researching about everything that happens during REM sleep.

What happens during REM sleep?

The body undergoes a number of different physiological processes including intense brain activity that is indistinguishable from being awake, the fast eye movement that gives REM its name, a complete paralysis of the body and accounts for the majority of your dreaming.

The reasons that these processes occur is less well understood but we know that REM sleep is important from experiments that have been conducted when depriving people and animals of REM sleep with numerous adverse effects.

REM sleep seems to have some function to different types of memory formation but it is unclear if this is due to these processes or if they are simply a byproduct of brain and body activity.

That’s the short and snappy answer, but read on for more detail, including a list of the processes that go on during REM sleep and also some information on dreaming and why we do it – including Freud’s thoughts on the matter!

What Happens During REM Sleep?

The following is a list of the notable physiological conditions that we have observed that happens during REM sleep:

1. Electrical activity in the brain (brain waves) is similar to being awake when measured by oxygen and glucose metabolism. It’s 11-40% lower in non-REM sleep.

2. Your eyes move back and forth beneath your eyelids – this is the process that gives REM sleep its name.

3. Areas of the brain that are active during REM sleep are the opposite of the ones activated during non-REM sleep. The amygdala being one example that is active that you may have heard of.

4. Male humans normally experience nocturnal penile tumescence (the scientist way of saying ‘morning wood’) during REM sleep.

5. Body temperature is not well-regulated which can cause you to become uncomfrotable with more extreme temperatures.

6. You experience the inhibition of motor neurons, which causes a complete paralysis of the body which is why you occasionally wake up not being able to move, the state being called ‘sleep paralysis’.

7. This is the part of sleep where you will do the majority (80% by one estimate) of your dreaming.

If you’re wondering exactly what is meant by the ‘rapid eye motion’ in REM sleep and what it looks like, check out this video, it perfectly shows what’s going on in a timelapse of 90 minutes in just 26 seconds.

What’s the purpose of REM sleep?

Observing the processes that go on during your REM sleeping state is relatively simple, deducing what those processes are for is much more difficult.

That said, we have made some progress in this area and I’ve outlined what I could find below.

·  Memory. Research into sleep has shown that it must have some effect on memory, we can deduce this from denying sleep to demonstrate that memory becomes impaired.

In the case of REM sleep, it seems like it helps build three types of memory. Procedural memory, like learning to throw a ball. Spatial memory, like remembering how to get around a new neighbrhood. Emotional memory, dealing with emotinoal events and using them to change behavior.

It has been hypothesized that the intense brain activity and dreaming that we experience during REM sleep is a result of the processing of information into long-term memory.

It’s strange to think about how dreams could come about simply as a product of our brain moving things around! One theory goes that the eye movement that gives REM sleep its name is from your brain looking to that place in the dream!

·  Defensive Immobilization. Another interesting idea is that REM sleep is in some way useful to us as a deterrent against predators because of its similarity to ‘playing dead’.

This reflex that many animals use as a defense mechanism shows strikingly similar characteristic to REM sleep, including paralysis of the body and the thermoregulatory changes.

·  No purpose. One popular theory is that REM sleep does not do anything in particular, that the physiological processes are simply byproducts of the random brain activation that occurs during sleep.

When the brain is doing one thing, it’s non REM and when it’s doing another, it’s REM.

These are just a few of the most common theories. The importance of memory in regards to sleep is well documented so we can say it’s likely that REM sleep shows some purpose there, but most of this is just conjecture.

Sleep is an extremely difficult area to study and it seems we just don’t know everything yet!

How do we know REM sleep is important?

Sleep is poorly misunderstood relative to other biological processes. It’s simple enough to see why we eat and why we drink, but would it not be more advantageous to spend those 8 sleeping hours awake and doing productive things like building shelters or gathering food?

(Or checking smartphones?!)

If you want a comprehensive answer to the questions “Why do we sleep?” then you should check out the big article I wrote on it, here I’m just going to talk about REM sleep.

We know that REM sleep is very important. We can test this by examining the effects of depriving humans or animals when they have been subject to REM sleep deprivation. Prolonged REM sleep deprivation in animals leads to death in experiments, and in both humans and experimental animals, REM sleep loss leads to sever behavioral and physiological changes.

More evidence comes our way in the prevalence of REM sleep in nature. If REM sleep were not so important to us, we might expect that there were some animals that function well without it.

As it happens, all mammals (which are the animals with the largest brains) and some birds exhibit some amount of REM sleep, so we can deduce that it must fulfill some important function in mammals.

Why do we dream?

In 1899, Sigmund Freud published his famous book called “The Interpretation Of Dreams”. He believed that the scenarios that took place in your dreams could be decoded and reveal hidden desires.

He wrote that, among other things, all dreams have some kind of connection to the previous day’s experiences and that each dream has a ‘latent content’ which is a hidden meaning that lies beneath the surface of what’s happening in the dream.

This was based more on conjecture than well-grounded science and is not a popular theory today.

Like many aspects of sleep, the true nature of dreaming is still a mystery to us, but we know it’s connected to REM sleep.

Studies have shown that sleepers awakened during the REM stage of sleep are more likely to be able to give narrative descriptions of dreams, theyr can describe their dreams better and report them as being longer. It is estimated that 80% of dreams happen during the REM phase.

One theory is that it aids in our creativity. After waking from REM sleep, we are more ‘hyperassociative’ which means that we are likely to see connections in things that we might not otherwise, a hallmark of the creative process.

This has been demonstrated by showing that people awakened from REM sleep have performed better in creative endeavors such as anagrams and problem-solving.

If the ‘why’ behind sleep is something that interests you then you might be disappointed to learn that we still do not have a full understanding. There are 4 competing theories that have been proposed over the years.

I outlined all this in my article on ‘Why Do We Sleep?’ along with my thoughts, I particularly found the 4th theory very intriguing. Click the link for more.


Ultimately, we don’t know that much about REM sleep or the other phases of sleep. The current scientific consensus seems to be that the most restorative and refreshing period of sleep is what we call ‘deep sleep’ and is the final phase of non-REM sleep.

This appears to be the type of sleep that is most useful in making us feel good and rested in the morning.

If that’s a goal of yours then you should have a look at my guide on getting more deep sleep. It’s a good complement to the information in this one.

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