The Architecture of Sleep

If you have ever been suddenly woken up, deep into the night, you’ll know it’s a very disorientating experience. When you wake up naturally, you rouse gently in a less confused state. This is because in these separate instances you have woken up in different stages of sleep.

Sleep has two main states, these are defined by the movement of our eyes:

  • Non-rapid eye movement (NREM)
  • Rapid eye movement (REM)

Having the correct proportions of each of these types is important to getting good and restful sleep.

The Sleep Cycle

Going from being awake to sleeping isn’t like flicking a simple on/off switch. Sleep has different stages and depths where your brain and body go through specific motions.

Within the seven to eight hours that we should be sleeping, we cycle through these NREM and REM stages in ninety-minute blocks …

  • To start, we initially plunge quickly through the stages of NREM sleep and trundle along in deep sleep.
  • After a while, we climb back into lighter NREM, eventually spending some time in REM.
  • We then drop back into deep sleep again at the start of the next ninety-minute cycle.
  • For every cycle, an increasing amount of time is dedicated to REM sleep, creating an asymmetric pattern.

But what happens during these phases, and why are they necessary?

NREM vs. REM Sleep

NREM Sleep

Stage 1 – this is light sleep, the first destination after wakefulness with tiny dream-like thoughts and easy arousal back to being awake.

Stage 2 – here, breathing slows and body temperature drops.

Stages 3 and 4 –this is deep sleep. Any sound, touch or light from the outside world is tightly controlled, with entry to the brain blocked. This is why it is hard to rouse someone from deep sleep.

This is an important stage for growing and repairing the body, increasing blood flow to various tissues, releasing important hormones and re-energizing.

The brain is reviewing the information that it has received throughout the day. Without the mental chatter of consciousness, our brain waves are long, slow and coordinated.

This pattern allows effective communication between different brain regions. Information is selected and pruned to form memories; the important memories being retained by creation of pathways in the brain, whilst needless ones are discarded from our temporary and fragile short-term storage.

REM Sleep

REM sleep is our dreaming sleep. Despite being asleep, our brain activity is very similar to when we are awake – lots of action; short, sharp and cluttered waves of electrical activity.

The exact functions of REM sleep are still not fully understood, but it is thought to be important in memory formation and learning. The memories selected in NREM sleep are now played back to us, helping us contextualize, learn and integrate them into the real world.

Despite being close to waking, our bodies are completely still, a mechanism to prevent us from turning this pseudo-consciousness into potentially risky sleep-walking or acting out dreams.

When deprived of REM sleep, both mental and physical dysfunction ensues. Indeed, when falling asleep after a period of REM deprivation, our sleep cycle patterns shift to snatch back as much of it as possible, favoring longer periods of REM sleep [1].

Where does snoring come into this?

There are no definitive rules as to when snoring and sleep apnea occur during the sleep cycle, but studies have found certain trends. It is thought that regular snoring occurs more during NREM sleep. This would explain why snorers don’t wake themselves up with the sound of their own snoring.

Obstructive sleep apnea is commonly associated with REM sleep [2], despite this some studies have found just as many cases of worsened apnea during NREM sleep [3].

References

  1. Walker M. Why We Sleep. London; Penguin, 2017: p107.
  2. El-Kersh K, et al. Effect of Sleep State and Position on Obstructive Respiratory Events Distribution in Adolescent Children. Journal of Clinical Sleep Medicine 2016; 12(4): 513-517. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4795277/
  3. Siddiqui F, et al. Half of patients with obstructive sleep apnea have a higher NREM AHI than REM AHI. Sleep Medicine 2006; 7(3): 281-285. https://www.ncbi.nlm.nih.gov/pubmed/16564214

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