Sleep Architecture

Some of you may know what healthy sleep feels like, but others may have never experienced it. No matter where you fall on the spectrum, it can be helpful to review what healthy sleep looks like to set reasonable expectations.

Sleep Stages

The different stages of sleep are broadly divided into two types:

  1. Rapid Eye Movement (REM)
  2. Non-REM.

This division in sleep is due to our bodies undergoing different processes within each stage…

  • In REM sleep: dreams and muscle paralysis occur — this is good because we aren’t acting out our dreams. However, we are unable to regulate our temperature by shivering if we’re too cold or spreading out if we’re too hot.
  • In non-REM sleep: Muscle tone is preserved — allowing us to regulate body temperature.

In total, there are 4 stages of sleep. The night begins with non-REM sleep. Non-REM sleep has 3 stages, before reaching Stage 4 (REM sleep):

Stage 1: nREM (light sleep)

Stage 2: nREM (light sleep)

Stage 3: nREM (deep sleep)

Stage 4: REM (REM sleep)

Picture from pipelineperformancegroup.com.
The four stages of sleep. Picture from blog.health.nokia.com

Lets unlock these stages a little more…

→ From being awake, you progress through each non-REM stage, 1 to 3.

→ At stage 3, you will be at your deepest sleep.

→ Your cycle then goes back on itself (i.e. goes from 3 to 1), until it eventually reaches REM sleep.

Stages of a normal sleep cycle. Picture from utzy.com

This progression from non-REM to REM takes approximately 90–110 min and is called an “ultradian cycle”. Your sleep consists of several of these ultradian cycles occurring in sequence throughout the night.

Now we’ve understood the basic structure that occurs within a night’s sleep (Stages 1–4), lets learn what each stage entails…

Stage 1 (non-REM)

Sense of falling is common in Stage 1. Picture from www.fleethoistics.co.uk
  • Stage 1 of non-REM is the lightest sleep (5–10% of a night) and is a nice transition between wakefulness and sleep.
  • It is common to experience a sense of falling, or “hypnic jerks”, in stage 1. This can be due to your nervous system and muscles relaxing when transitioning from wakefulness to sleep. During this slowing down process, nerves might misfire, which results in the muscular spasm.
  • We often retain some perceptual awareness in stage 1, so if we hear our names, we’ll wake up, but we are relaxed enough to drift to sleep.

Stage 2 (non-REM)

Body gets ready for deep sleep in Stage 2. Picture from www.fleetholistics.co.uk
  • Stage 2 is also a light stage of sleep, but deeper than stage 1, which means that it’s harder to arouse someone once they hit this stage. The body gets ready for deep sleep: heart rate slows and body temperature drops.
  • Most of our sleep is spent in this stage — approximately 45–65% of a given night.
  • Stage 2 is also sometimes referred to as “unequivocal sleep” because we know that you’re sleeping by this point based on changes in your brainwaves.
  • Some of the benefits of this stage of sleep include the encoding of semantic (e.g., words, facts) and episodic (e.g., events, experiences) memories.

Stage 3 (non-REM)

Body is in deeper sleep at Stage 3. Picture from www.fleetholistics.co.uk.
  • Stage 3 is the final stage that you’ll reach in non-REM, and it is also known as deep sleep, slow-wave sleep, delta-wave sleep, or restorative sleep.
  • The body is in slightly deeper sleep compared to stage 2. Stage 3 is the hardest to wake up from and is characterised by slow delta brain waves.
  • Stage 3 is where we get our bone, muscle, and tissue repair, but only makes up 20–25% of a night once we reach adulthood.

Stage 4 (REM sleep)

Most likely to experience dreams in Stage 4. Picture from www.fleetholistics.co.uk. .
  • After moving to stage 3, you quickly rise back up through stages 2 and 1 before entering your first bout of REM sleep (stage 4).
  • REM is considered a light stage of sleep and makes up the remaining 20–25%. This stage typically occurs after being asleep for around 90 minutes. However, the REM stage increasingly gets longer as the night goes by, which can eventually last up to an hour.
  • As the name might suggest, your eyes move rapidly in different directions in this stage. Also, one might experience vivid dreams and sleepwalking.
  • REM sleep is important for processing and encoding emotional and procedural (e.g., how to tie your shoes) memories.

Sleep cycles

  • The first third of the night is characterised by more deep sleep and little REM.
  • As your deep sleep tails off, REM will increase, leaving you with ultradian cycles consisting of stages 1, 2, and REM in the latter parts of the night.
  • This fluid structure allows us to capture the benefits contained within each stage of sleep even if you don’t get all the sleep you need on a given night. It also means that our bodies are adapt to sleep loss. Meaning if you lose sleep on a few nights, your body will differentially make up the types of sleep you lost the following nights automatically.
  • Your night is dominated by light sleep (comprised of stages 1 and 2 and REM), accounting for 80–90% of a given night. These will gradually give way to more Stage 2 through adolescence into adulthood.
These cycles are not static. The proportions of each stage of sleep will change as the night progresses. Picture from howsleepworks.com

Sleep Quantity

Recommended number of hours of sleep required. The National Sleep Foundation.

Just as the proportions of sleep stages change over the course of your life, the amount you sleep changes as well.

  • E.G. Younger people tend to get more REM and deep sleep, as they are still growing. However, there will still be people who are perfectly healthy at 6 hours or 10 hours, but they are statistically rare (around 5% of the population).

Infancy

Picture from askdrsears.com
  • At the beginning of your life, you needed a lot of sleep to support rapid growth and development. On average, you probably needed roughly 9–17 hours per night as an infant.
  • 70–80% of infants’ sleep time is spent in Stage 4 of the sleep cycle (REM sleep) in preterm infants and 50% in term infants. This decreases to 30% of sleep time spent in REM in 6 month infants. Adult levels of sleep time spent in REM (20–25%) is reached at 5 years of age.
  • The greater time spent sleeping in infants has been suggested to reflect the crucial role sleep plays in fostering optimal brain development, cognition, and behaviour.

Childhood-Adolescence

Picture from schoolfamily.com
  • As you moved through childhood, the amount of sleep required decreased from this amount decreased to 12–15, but you probably still needed 9–10 hours in adolescence.

Adulthood

Picture from livescience.com
  • Once you reach adulthood (aged 18+), the amount for most people settles around 7–9 hours per night for the rest of their lives.

Older adults

Picture from lifestyleoptions.com
  • After the age of 65, most people are recommended to get an average of around 7–8 hours per night, so not a huge difference to that at adulthood (aged 18–64).

Athletes

The amount of sleep you need can also fluctuate based on your activity level, metabolism, and stress levels.

For example…

  • Serious athletes generally will need at least 1 additional hour of sleep per night compared to same-aged peers.
Picture from telegraph.co.uk
  • In 2012 Olympics, Usain Bolt became the first man to win 6 gold medals in sprinting. And what does he consider to be the most important aspect of his training?…

“Sleep is extremely important to me — I need to rest and recover in order for the training I do to be absorbed by my body” — Usain Bolt.

Thats right, sleep.

Remember these are just guidelines, so it’s important to figure out how much sleep you need!

Tips

Now that you have a better understanding of the normal sleep process, read these three tips to become more informed on healthy sleep.

  1. Be patient — your sleep troubles developed over time, so the processes will take time before a normal sleeping pattern is reached.
  2. Healthy sleepers take approximately 15-20 minutes to fall asleep.
  3. After each sleep cycle, even healthy sleepers will have brief awakenings.
Click here to read our next blog that discusses the mechanisms of a healthy sleep in more detail, and provides another 3 useful tips you can use yourself to help improve your sleep.