NREM & REM: The Two Types Of Sleep

The Importance of REM & NREM Sleep

Where once we thought sleep was just one state of being, we now know that it is, in fact, two completely different states of sleep. These two stages were defined by their ocular features- non-rapid eye movement (NREM), and rapid eye movement (REM), as they were the first discernable differences in this sleep discovery. When sleeping, the body does not just switch between these two states once per night, but instead, continuously cycles through the two until it’s time to wake, known as our sleep cycle.

If you have ever watched another person sleep at night, you have most likely noticed movement underneath the eyelids, as if the eyes are darting back and forth. This is the most typical sign of REM sleep or rapid eye movement sleep.

Many have probably heard this term before when discussing sleep, but what about its other half, NREM sleep? REM sleep is only one part of the body’s sleep schedule- NREM, or non-rapid eye movement, is the other side of the metaphorical sleep coin.

The Continuous Sleep Cycle

Each of the two sleep states dominates the brain for approximately ninety-minute cycles. Yet, the levels and stages of the two change depending on the time of night. As illustrated in the table below, there are four different stages to NREM, but only one for REM.

The first half of the night is defined by NREM sleep, as the body cycles through stages 1, 2, 3, and 4. Much of the early AM focuses on slow-wave sleep. Stages 1 through 4 refer to how deep the NREM sleep is, and how difficult it is to wake a person from this state. Starting in the latter half of the night, and gearing up in the early morning, REM sleep takes over.

Figure 8, page 82 in Matthew Walker's book Why We Sleep
So what’s the difference between these two states, and how do they both influence the body?

NREM Sleep and Brain Cell Synchronization

Where once we believed sleep was a state of hibernation, of shutting down the body’s system, we now know this far from the truth. In actuality, the brain and body are both in a state of perpetual activity.

Deep NREM sleep is when the millions of brain cells working within the body decide to operate in unison. This unbelievably adept neural collaboration between cells is what defines the deep slow-wave sleep stage, and it is the default mode of sleep. This brain cell synchronization cultivates a plethora of mental and physical benefits, with the most important being the saving of memories, from short term storage to long term.

Consider this for the moment- all of the brain cells firing off together are a group of synchronized swimmers hanging out at the public pool, the brain. Typically these cells, or swimmers, are splashing about, doing their own thing in the pool of our brains when we are awake.

When sleep ensues, and the first NREM cycle begins, these neurons start to operate together, commencing the system’s synchronized swimming routine. It is during NREM that one member of a swim team located in one region of the brain, can swim to a separate part of the brain, and teach this swim group their routine.

This passing along of a synchronized routine is symbolic of the transporting of stored information and experience. Each individual slow wave of NREM sleep is a synchronized swimmer passing along stored memories to another part of the brain. Each night these brain cells, or swimmers, will teach the routine, or the day’s experiences and memories, to other members that are located in the deeper part of the brain where long-term memory is stored.

With this in mind, NREM can be defined as the state of sleep that fosters information from the outside world and transfers it into stored memories. The brain cells or synchronized swimmers are cementing the routine they just learned.

REM, Dreaming, and Paralysis

When mapping electrical brain activity, it is impossible to tell the difference between a state of wakefulness with that of deep REM sleep. Both states activate the same parts of the brain. Further studies have uncovered that certain parts of the brain are actually up to 30% MORE active during REM sleep than they are when we are awake.

REM sleep is similar to the brain’s awake state, as those brain cells, or synchronized swimmers, are back to splashing about, swimming in all directions, and are, therefore, desynchronized. At this time, each swimmer is processing its own swim routine or informational pieces.

With so much desynchronized activity happening in the brain cells at this time, the brain does something unique to the REM state– it turns off all muscle activity, effectively paralyzing the body. Such paralysis does not affect the involuntary muscle movements like breathing, which continue to operate as a means to maintain life.

The only way sleep scientists can tell if a person is awake or in REM sleep, is by mapping muscle activity alongside the electrical brain activity. By monitoring the state of the muscles, whether they hold tension (which they do in both awake state as well as in NREM) sleep scientists can tell if an individual has reached the REM cycle stage, whereby their body is basically in a rag-doll state of being, completely limp.

REM sleep is when dreaming happens. This paralysis is a form of self-preservation, stopping the brain which is dreaming, from acting out the brain activity in real life. With all the brain cells desynchronized and splashing about, it is paramount that this brain activity does not translate to physical activity. Only after the REM cycle is completed, can the body come out of this paralysis. Sometimes people’s brains snap awake while their body stays in this paralyzed state, this is known as sleep paralysis.

REM Sleep Effects Social Interactions and Creativity

REM sleep is not only a state for dreaming, but it also facilitates and strengthens connections that the NREM brain cells, or synchronized swimmers, have just created. The routines/ memories that have been passed along to long-term storage are then backlogged with all other routines/memories the swimmers have learned and catalogued since birth.

It is this compiling of data that happens in REM sleep, which builds upon an individual’s ability to read emotional and social cues, as well as regulates our emotions and rationality.

This dreaming state also fuels our creativity. By compiling a backlog of all memories, our synchronized swimming routines, the brain can then create its own, greater swim routine, using all other routines as a foundation for new ones. It is during REM in which these connections are made and built upon. That’s why you can sometimes wake up with a completely new meaning or understanding of something- your brain made that new link in REM sleep. Daytime napping that achieves a whole cycle of NREM and REM sleep has also been linked to improved memory retention of things learned that day.

Why Eight Hours of Sleep Matters to NREM and REM Cycles

When people are having issues with their technology, many suggest turning it off and on again. Sleeping, and cycling through NREM and REM states, is essentially the same thing. By sleeping, our brain is making new connections and can come to conclusions that will pop into our head when we wake up.

Typically 8 hours of sleep is required to create and cement these connections in the brain. Individuals that lose just two hours of sleep might assume they are cutting down on their NREM and REM cycles by only 25%. Surprisingly, however, this is not the case.

Depending on which side of sleep was lost- whether going to bed later, or waking up earlier than usual- it can cut down on NREM and REM cycles by 60 to 90%!

This drastic reduction in effectiveness is a huge problem because an individual needs a balance of both states to fully benefit from sleep. Achieving full NREM sleep allows the brain to deposit memories from short-term storage to long-term, while REM sleep creates and cements these new connections in the mind each night. To learn more about how important these states of sleep are, check out our article on 4 Ways Sleep Affects Brain Function Big Time

So next time you’re thinking of cutting your sleep short, think again!