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The History of Sleep: How We Came to Discover Sleep Stages

May 8, 2020

It’s safe to say that humans have been sleeping since the dawn of humanity… but in spite of this, much of our understanding did not occur until the 20th century. Let’s take a look at breakthroughs through the history of sleep that have brought us closer to understanding its stages.

Henri Pieron (1881-1964)

Henri Piéron was a French Scientist who in 1913 authored a book entitled “Le probleme physiologique du sommeil,” which was the first documented text to take a deeper look at sleep from a physiological perspective. This work is usually regarded as the beginning of the modern approach to sleep research. 

Piéron ran interesting experiments involving sleep-depriving dogs and then attempting to induce sleep in another dog by infusing them with brain extracts, serum and CSF from the sleep-deprived dog.” Throughout his career, he was focused on studying the physiological basis of behaviour as well as the science of dreaming.

Nathaniel Kleitman (1895-1994)

Dr. Nathaniel Kleitman was an American physiologist and sleep researcher who earned a Ph.D. from the University of Chicago’s Department of Physiology. Soon after completing his thesis of “Studies on the physiology of sleep” he joined the faculty in 1952. Known as the Father of American sleep research, he focused a large majority of his research on circadian rhythms and published the encyclopedia Sleep and Wakefulness in 1939. 

Then in 1953, Dr. Kleitman and his student Dr. Eugene Aserinsky discovered rapid eye movement (REM) during sleep.  This breakthrough in sleep science demonstrated that not all phases of sleep are completely passive and was arguably the most critical finding in sleep research in the twentieth century.

 

sleep cycles, sleep meditation
Kleitman (at left in both photos) and his student Bruce Richardson camped out in Mammoth Cave in Kentucky to study the body’s ability to conform to a non–24-hour cycle.
SUBHADEEP DUTTA GUPTA. Image taken from www.the-scientist.com

 

Kleitman often used himself as a subject in his sleep research, testing one of his hypotheses—that the 24-hour clock could be modified— by spending 32 days living in a deep cave in Kentucky with a student, where the two imposed a 28-hour day on themselves. Other interesting self-testing included an underwater submarine during World War II, a trek above the Arctic Circle, and staying awake 180 hours – to which he noted that “forcing someone to stay awake was an effective form of torture.” We would have to agree.

Prior to the incredible work produced by Kleitman, it was thought that the brain and body were in a completely inactive state during sleep.  By the late 1950s, another one of Dr. Kleitman’s students published research describing the cyclical nature of sleep (1).  Since then, sleep research has largely become focused on disordered sleep patterns, the implications of poor sleep on our health, and factors that contribute to improved sleep quality. 

Have you ever wondered what exactly happens when we sleep? 

We now know that sleep is about more than getting physical and mental rest and that not all parts of our physiologic and biochemical processes are inert while we sleep–certain hormones are active, memories are organized and stored, and our tissues heal.  We also know that the amount of sleep required varies depending on your age—infants, children, and teenagers need more sleep than adults since they are actively growing.

Sleep stages, sleep meditation, sleep help

The Sleep Cycle

We know that there are two types of sleep: non-REM and REM sleep.  We also know that within non-REM sleep, there are three different stages (it used to be four) where distinct brain activity occurs.  Every night we cycle through these stages several times for different lengths of time, but generally speaking non-REM cycles are longer in the beginning of the night while REM cycles are longer later in the night.

Here’s a fun visual representation we like from the helpful folks at Udacity:

Sleep Cycle – Stage 1 (Non-REM):  As soon as you start drifting off, your brain waves slow down into the alpha and theta zones.  This is a light stage of sleep where you can still be woken up easily.  Your muscles start to relax and your heart rate, breathing, and eye movements get slower.  Stage 1 non-REM lasts for only a few minutes and warms you up for deeper sleep (2).

 

Sleep Cycle –  Stage 2 (Non-REM):  Most of your total sleep time is spent in stage 2.  In this stage, your muscles continue to relax, heart rate and breath rate slow more, body temperature drops, and your eye movements stop (3).  Although overall your brain activity slows, your brain will experience “sleep spindles,” or short bursts of electrical activity that last for less than 2 seconds each. The term spindle is used because the shape of sleep spindle burst is often like that of a yarn spindle.  These are believed to play an important role in organizing your memory (4).

sleep stages, sleep meditation, sleep spindle
Stage-independent, single lead EEG sleep spindle detection using the continuous wavelet transform and local weighted smoothing (Tsanas, Athanasios and Clifford, Gari)

 

Sleep Cycle – Stage 3 (Non-REM):  This is where deep sleep occurs.  Your brain starts operating more in slower delta waves, and in order to feel rested in the morning, you need high-quality Stage 3 sleep.  Your heart rate and breath reach their lowest points during this stage and your muscles will be fully relaxed (3).  Furthermore, this is where a lot of tissue repair, growth hormone production, and immune system optimizing occur (2). You’ll be less responsive to your alarm clock or spouse trying to wake you up (although perhaps a bucket of ice water will do the trick)(maybe don’t try that at home).  

 

REM:  This stage first occurs about 90 minutes after you fall asleep and is when your brain starts to become more active and are most similar to the wakefulness pattern.  Your heart rate increases, your breathing becomes faster, and your eyes move rapidly while they are closed (hence the name “rapid eye movement” sleep).  This is also the stage where most dreaming occurs, and usually the phase where we remember our dreams more vividly (5).  Like non-REM sleep, REM sleep is also important for memory and learning and also seems to affect mood.  The amount of REM sleep we get appears to be highest when we are infants and then declines in adulthood (6).

sleep stages

How Can We Improve Sleep?

It’s clear that both non-REM and REM sleep stages are important to our sleep quality and in turn our overall health.  There are many factors that influence sleep including genetics, age, stress, and medications.

Tips on Improving Deep (NREM) Sleep:

Much of the focus is on effectively getting into Stage 3 non-REM sleep as this is where deep sleep occurs.  Without adequate deep sleep, we are more likely to feel unrested upon waking.  Having a proper winding down routine before bed is essential to enhancing your sleep quality. 

These sleep hygiene tips enable your brain and body to get into a relaxed state more easily (7):

  • Avoid stimulants (ie. caffeine) after lunch
  • Exercise daily, but not right before bedtime
  • Turn off all screens at least 1 hour before bed
  • Have a warm shower/bath or a cup of herbal tea
  • Meditate daily

It’s equally important to set up your sleeping environment so that you are less likely to be disturbed in the middle of the night (7). 

  • Make sure your room is pitch black or use a sleep mask over your eyes
  • Do your best to avoid having disruptive pets, children, partners sleep with you 
  • Set your room to a comfortably cool temperature 
  • Reserve your sleeping space for only sleep and intimacy—avoid eating, doing work, and watching TV in bed as it may lead to bad habits

Tips On Improving REM Sleep:

Since the discovery of REM sleep in the 1950s, there has been extensive research on the effects of poor REM sleep and how to prolong REM sleep in adults. Lower REM sleep time is associated with poor memory, mood dysfunction, and less ability to focus.  However, it’s all about balance as too much REM sleep can lead to some of the same concerns.

Research has shown that caffeine, nicotine, and alcohol all decrease REM sleep time (7). Therefore, avoiding those things can help increase your REM time.  Meditation also appears to benefit REM sleep time (8).  

sleep stages, sleep meditation, sleep better

Sleep & Meditation

Research has shown that meditation, in combination with other healthy lifestyle habits, has the ability to help improve overall sleep quality by decreasing the amount of time it takes for you to fall asleep and decreasing the number of times you wake up in the night.  Certain forms of meditation also appear to distinctly enhance REM sleep (8)(9).  Meditation is also an important key to improving symptoms of high stress and persistent feelings of anxiousness — both of which can contribute to poor sleep patterns.

Depending on what are doing throughout the day and which phase of sleep we are in at night, our brain will predominantly exhibit certain brain wave patterns (10).  

  • Alert wakefulness: beta
  • Relaxed wakefulness: alpha
  • Stage 1 NREM sleep: mostly theta, some alpha
  • Stage 2 NREM sleep: theta with sleep spindles and K complexes 
  • Stage 3 NREM sleep (deep sleep): delta
  • REM sleep: variable, but high activity similar to awake patterns

Like sleep, meditation favours activation of the parasympathetic (“rest and digest”) nervous system.  In both states, breath rate decreases, heart rate decreases, and blood pressure drops, among other physiological effects. During meditation, we are getting into the alpha and theta brain waves—the same ones that occur in the earlier stages of our sleep cycle (8).  However, meditation is not a direct replacement for sleep, as meditation does not activate the deep sleep (delta) brain waves which are necessary for complete rest.  Instead, meditation is a useful tool for improving the quality of nearly all stages of sleep.

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References:

  1. Stanford University: A Brief History Of Sleep https://web.stanford.edu/~dement/history.html
  2. Sleep.org: Understanding Sleep Cycles: What Happens While You Sleep https://www.sleep.org/articles/what-happens-during-sleep/
  3. National Institute of Neurological Disorders and Stroke.  Brain Basics: Understanding Sleep https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Understanding-Sleep#2
  4. The Journal of Neuroscience, Dec 7, 2011 31(49):17821-17834. Sleep Spindles in Humans: Insights from Intracranial EEG and Unit Recordings. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3270580/pdf/zns17821.pdf
  5. Harvard University: Natural Patterns of Sleep. http://healthysleep.med.harvard.edu/healthy/science/what/sleep-patterns-rem-nrem
  6. Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Neuroscience. 2nd edition. Sunderland (MA): Sinauer Associates; 2001. Available from: https://www.ncbi.nlm.nih.gov/books/NBK10799/ [Accessed 10 April 2020].
  7. Harvard University: External Factors That Influence Sleep http://healthysleep.med.harvard.edu/healthy/science/how/external-factors
  8. Nagendra RP, Maruthai N, Kutty BM. Meditation and its regulatory role on sleep. Front Neurol. 2012;3:54. Published 2012 Apr 18.  Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3328970/ [Accessed 11 April 2020].
  9. Black, D., O’Reilly, G., Olmstead, R., Breen, E. and Irwin, M. (2015). Mindfulness Meditation and Improvement in Sleep Quality and Daytime Impairment Among Older Adults With Sleep Disturbances. JAMA Internal Medicine, [online] 175(4), p.494. Available at: https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2110998  [Accessed 10 April 2020].
  10. National Sleep Foundation: Stages of Human Sleep https://sleepdisorders.sleepfoundation.org/chapter-1-normal-sleep/stages-of-human-sleep/
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