REM sleep and NREM sleep

Scientists differentiate between REM sleep and the three NREM (non REM) sleep stages. They use i.a. brain, muscle and eye activity to distinguish the current sleep stage.

For instance, the REM sleep brain waves are quite like those from you're either awake or in NREM sleep stage 1. But when looking at the muscle and/or eye activity you can tell the precise sleep stage.

The 4 Sleep Stages

There used to be 5 sleep stages. American Academy of Sleep Medicine (AASM) changed this in 2007.

As of 2007, there are 4 sleep stages. These are:

1. "doze off" - sleep stage 1
2. light sleep - sleep stage 2
3. deep sleep - sleep stage 3
4. REM sleep - sleep stage 4

Together, we call the first 3 sleep stages for NREM sleep (non rem sleep). That's the sleep stages, that are not REM sleep.

Sleep cycles

A sleep cycle is the name for one round trip through all 4 sleep stages. A round tour through sleep cycle stages, takes between 90 - 110 minutes. Ideally you should complete 4 - 6 sleep cycles every night.

In your first sleep cycles, you spend relatively more time in the deep sleep stage, and less time in REM sleep. After completing 2 - 3 sleep cycles, you may not experience anymore deep sleep that night. Instead, you get to sleep more REM sleep.

You primarily deprive yourself from all the good things, REM sleep does for you, if you don't sleep enough!

It is normal to wake up after completing each sleep cycle. That's no cause for concern, provided you fall asleep again within a short while.

What happens in the sleep stages?

The best way to explain each sleep stages is by using a library as an analogy of your brain. So if you imagine your brain is a library, with new books arriving continuously, in one steady stream. Meanwhile, customers are all over the place, looking at all the book shelves.

Stage 1 - The 'Doze Off' Stage

In our library analogy, this is where the library guards prepare shutting down for the night. They check if all customers and employees have left the building. If someone or something is not quite ready for night mode, it's quick and easy to get back to day mode.

The 'guards' have now shut off the lights and initiated the first stage of light sleep. They have tested if it was 'safe' to shut you down. You sleep very light in this stage, and you can wake up easily. You would often even deny having been asleep, if woken up from this stage.

If someone is in this stage of sleep, and you e.g. turn off the TV, they will wake up and say: "Hey ... I was watching that" - and they would not know (or admit), that they we're in fact asleep.

During this stage your pulse gets slower, as does your breathing and eye movements. Your muscles starts relaxing, and you may experience occasional muscle twitches. We call these the myoclonic jerk, and they are no reason for concern.

Your brain waves are now slower than, when you were awake. Your heartbeat and eye movements also slows down.

This stage lasts 5 to 10 minutes.

Stage 2 - Light Sleep

Following the library analogy. Now it is time for the library personnel to move all the newly arrived books to the correct book shelve. That means putting it next to other books on the same topic. This process also makes room in the short term storage, for all the books, that will arrive tomorrow.

They have tested sleeps effect on your memory, in many independent scientific experiments. The results are clear. Those who had the most spindles, were also the ones who could best remember e.g. word pairs. If you are studying for e.g. an exam, you should aim for an 8-hour sleep, rather than 6. You will remember and understand the material much better. This has been tested scientifically.

Some sleep scientist believe that those who have the most spindles, are the most intelligent people. You experience the most spindles during the latest two hours of an 8 hours sleep.

Likewise, it seems that the spindles also help you remember movements. Many musicians and athletes have experienced inexplicable improvements overnight.

The spindles also seem to protect your sleep by not waking you up. When they occur, you are less likely to not respond to sounds, touches etc. If there was an unfamiliar noise from the street, you wouldn't wake up if it happened during a spindle. It appears, that the brain sends out a K-complex signal. That seems to ask your 'control center' permission to temporarily not respond to stimuli. Shortly after it gets permission to proceed, you get the spindles.

In sleep stage 2, your muscles are even more relaxed that in stage 1. Your brainwaves and heartbeats slows even further down, and your body temperature drops.

Stage 3 - Deep Sleep

In our library analogy, it is now time for the cleaning staff to make the library spotless. Everything gets hosed down. There will be no dust, cobwebs, bits of paper or anything else unnecessary in the library.

When woken up from this stage, you would need 30 - 45 minutes before you start making any sense. That's probably the time it takes to empty the cleaning fluids out of the brain.

If you talk in your sleep, walk in your sleep, wet your bed, it happens while you are in the deep sleep stage.

You can have dreams in this stage, but it is rare. If you do, they tend to be more realistic, than the dreams you have in your REM sleep.

Stage 4 REM Sleep

In our library analogy, we can compare REM sleep to the process of updating all indexes. This way, we can find the information at warp speed, when required.

REM sleep is great for creativity and problem solving. REM sleep generates new, unexpected connections, between what you already know and the information in the new book.

Many scientists call REM sleep for the dream sleep stage. Most of the dreams, we can remember, happen in REM sleep. You can however have dreams in the deep sleep stage as well. The dreams you experience during your REM sleep, can be fairly unrealistic.

Advertisement

Let's say your new book/experience was about e.g. outrunning a T-Rex dinosaur. REM sleep will then probably categorize the book with the time you escaped a smilodon. REM sleep is also associating these two experiences. This way, you're better prepared to escape other dangerous animals in the future.

One good guess of why we dream, is that the brain looks through old experiences, to associate them with the new ones. Another interesting guess is, that the brain 'removes' the strong emotions from experienced danger. This idea has helped lots of veterans with PTSD.

Your muscles are paralyzed while in REM sleep. This happens to protect you, prevent your physical body from acting out your dream.

Otherwise, you would attack the dinosaur, outrun Usain Bolt or throw a punch at George Frazier. I trust whoever sleeps next to you is happy for the paralysis.

Advertisement

If you suffer from REM sleep behavior disorder, your muscles aren't paralyzed completely, during REM sleep. In another sleep disorder, narcolepsy, this paralysis can happen while you are awake.

For healthy adults, the only thing, you can move during REM sleep is your eyes. Your eyes move rapidly from side to side beneath your closed eyelids. The name REM is an abbreviation of Rapid Eye Movement.

If you keep a rat awake for a longer period (up to 10 days), it would almost only sleep REM sleep, in the first many hours of sleep. This proves, that when it really matters, REM sleep is the most important of all sleep stages.