Sleep Series (1): The Science of Sleep and Circadian Rhythms

April / 2021

If you are concerned with leadership and talent, you should be concerned about sleep – a key to good health and peak performance.

Sleep is a critical component of life and survival for all living animals, especially humans.  While we still do not have an exact understanding of why we sleep or what biological processes are occurring during sleep, we do know that our bodies require significant periods of sleep on a regular basis to consolidate memories and learning, restore and rejuvenate, grow muscle and repair tissue, synthesize and balance hormones, and clear out waste products (i.e., metabolic toxins) from our brain via a lymphatic system that is only activated during slow-wave sleep.  In fact, during nighttime sleep our brain is very active – there is almost as much neural activity during sleep as there is during waking periods.

During the night, our brain cycles through two major types of sleep.  Non-REM sleep involves high amplitude, low-frequency rhythms, whereas REM (rapid eye movement) sleep is characterized by low amplitude, high-frequency EEG rhythms.  There are 4 stages of non-REM sleep that occur before we reach the REM stage.  According to results from physiological measurements, REM and non-REM sleep seem as different from each other as either is from wakefulness.  

The first state in a sleep cycle is light sleep (non-REM stage 1), followed by deeper sleep (non-REM stages 2-4), and a dream state referred to as REM sleep.  After the first REM stage is completed we cycle back down through non-REM stages, 4, 3, and 2 before cycling back up through them again to REM.

A full sleep cycle lasts about 90 minutes the first time through and is normally repeated several times each night, growing shorter each time.  The last two sleep cycles of the night are usually alternations between stage 2 and REM sleep.  Brains that are deprived of REM sleep will subsequently produce more of it (i.e., REM “rebound”). 

It is likely that each cycle of sleep has distinct neurorestorative processes.  This means it is important not only to get a sufficient quantity of sleep every day but also to get the quality of sleep your brain and body need.  This means getting sufficient REM and slow-wave sleep on a regular basis.

Also relevant to our understanding of sleep are our circadian rhythms.

  These are cycles of sleep and wakefulness lasting about one day.  Circadian rhythms occurring in an environment free of natural time cues (e.g., living in a dark cave) stabilize at a little over 24 hours.  At any given moment our degree of alertness depends on the part where we are in our circadian rhythm. 

People fall somewhere on a continuum, with “morning people” being on one end and “evening people” being on the other end of that continuum, but this changes as we age.  Young people tend to be “evening people” or to have no preference; while older people (e.g., over 65) are “morning people.”  There is reason to believe that nocturnal lighting, especially the “blue” lights of computer screens and smartphones has a disruptive effect on our circadian rhythms.

Although many aspects of sleep remain scientifically mysterious to us, there is no question that getting sufficient amounts of quality sleep on a regular basis is a pillar of human health, wellbeing – and performance.  Most adults require 7-9 hours of sleep per night for optimal health

Some people need less sleep than others – there are individual variations around the universally acknowledged 8 hours.  The quality of sleep during those hours is also important.  Sleep efficiency is the ratio of the total time spent asleep in a night compared to the total amount of time spent in bed (a sleep efficiency of 85% is typical).

There are both psychological and physical consequences associated with chronic sleep deprivation. 

Negative psychological and cognitive consequences of chronic sleep deprivation include: 

  • Irritability
  • Cognitive Impairment
  • Memory Loss
  • Impaired moral judgment
  • Impaired judgment regarding risk-taking
  • Impulsivity
  • Restlessness
  • Distractibility
  • Poor concentration
  • Depression
  • In acute situations, even hallucinations, and paranoia

The physical and medical effects on the human body are also profound.  Chronic sleep deprivation contributes to impaired immune functioning, increased risk of Type 2 diabetes, increased risk of heart disease, obesity, impaired psychomotor skills, and body aches and pains.

All of this is to say that both quantity and quality of sleep are critical for good health and maximum performance.  In another post, I’ll talk about some of the things you can do to help yourself sleep better.

About the author

Chris Frueh
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Christopher Frueh, Ph.D. is a clinical psychologist, Professor of Psychology at the University of Hawaii, and Clinical Professor of Psychiatry, University of Texas Health Science Center, Houston, TX. He has thirty years of professional experience working with military veterans and active-duty personnel and has conducted clinical trials, epidemiology, historical, and neuroscience research, primarily with combat veterans. He has co-authored over 300 scientific publications, including historical analysis of U.S. Army suicides dating back to 1819 and a current graduate textbook on adult psychopathology. Professionally, he has worked with combat veterans since 1991 and devotes much of his time to the military special operations community. He has also published commentaries in the National Review, Huffington Post, New York Times, Time, and Washington Post; and has been quoted in the Wall Street Journal, The Economist, Washington Post, Scientific American, Stars and Stripes, USA Today, Men’s Health, and Los Angeles Times, among others. Under the pen name Christopher Bartley, he has also published nine novels, including THEY DIE ALONE and most recently, A SEASON PAST.

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