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The Mysteries of Sleep: How This Small Death Helps Us Live

We learn why the intermediate stage between life and death is such an important, essential, and very productive part of our life. Our internal clock.

Photo of a sleeping toddler in the bed. You can see scalp, face and arms.© CC0, dagon_, Pixabay

1. Foreword written by editorial staff

In a text attributed to Homer (approx. 850 BCE), he called sleep death’s little brother. Buddha (Siddhartha Gautama, approx. 500 BCE) described sleep as the small death and saw sleep virtually as a spiritual rebirth. In the Quran, sleep is a type of death: Allah takes the souls at the time of their death, and those that do not die [He takes] during their sleep. Then He keeps those for which He has decreed death and releases the others for a specified term.​ (Surah 39, Verse 42 (43),

In contrast, today the small death (la petite mort) at least applies to the orgasm. In some interpretations, however, sleep is the small death in which the unconscious comes to the surface. Both have to do with a loss of control, and both are “productive.” However, a person can also experience the feeling of a small death when a romantic relationship or deep friendship ends.

Rainer Maria Rilke - Das Stundenbuch (The Book of Hours)

Rainer Maria Rilke wrote the following in Das Stundenbuch (The Book of Hours):

Ich kann nicht glauben, dass der kleine Tod,
dem wir doch täglich übern Scheitel schauen,
uns eine Sorge bleibt und eine Not.
Ich kann nicht glauben, dass er ernsthaft droht;
ich lebe noch, ich habe Zeit zu bauen:
mein Blut ist länger als die Rosen rot.

Unofficial translation:

I cannot believe that the small death
whom we see every day hovering over our head,
remains a concern and a necessity.
I cannot believe that it is a serious threat;
I still live; I have time to build:
my blood is flowing as deeply as the roses are red.

Picture with bed in dark cornfield with kid counting sheep. Right the setting full moon.© CC0, Gellinger, Pixabay
Sleep disorders can seriously interfere with normal functioning. Types of disorders include arousal disorders, dyssomnias, parasomnias associated with REM sleep, and also other parasomnias.

Arousal disorders, dyssomnias and parasomnias

Arousal disorders include confusional arousals, sleepwalking, and night terrors.

Dyssomnias often involve stereotypical movement disorders, hypnic jerks, talking in your sleep, and nightly leg cramps or spasms of the musculature.

Parasomnias associated with REM sleep include, for example, nightmares, sleep paralysis (narcolepsy and cataplexy), penis disorders that appear during the night, asystole (flatline) associated with REM sleep, and rapid eye movement sleep behavior disorder (RBD).

Other parasomnias include Bruxism, nocturnal enursis, somatoform disorders, nocturnal paroxysmal dystonia, sudden death, primary snoring, child sleep apnea, sudden infant death syndrome (SIDS), and benign neonatal sleep myclonus.

The link to the topic of sleep on Wikipedia is very informative and explains just how important sleep is for us. Sleep deprivation is a type of torture. Why do even insects and worms need sleep? Well, we do know that genes are the reason, and we have already decoded some tasks of such genes. But the mystery has not yet been solved.

Nevertheless, the following paper is very interesting. It shows us how important it is to get “healthy sleep.” In "What makes a good night’s sleep?", we also describe in detail the necessary steps to achieve this.

We would like to thank Dr. Gottfried Schatz for sending us his paper to publish — after it appeared in the Neue Zürcher Zeitung (NZZ, Swiss newspaper).

2. The Mysteries of Sleep: How This Small Death Helps Us Live

According to Hermann Alexander Diels (1848–1922) in "Die Fragmente der Vorsokratiker" (The fragments of the Presocriatics, 17th ed. 1974, p. 171), the Greek philosopher Heraclitus of Ephesus made the following statement: Those who are awake have a single and common world, but in sleep each person turns away from this and enters their own world. Heraclitus saw sleep as an intermediate stage between wakefulness and death.

Painting oil on canvas, NIghtmare, by Johann Heinrich Füssli (1741-1825) Painted 1781.© Public Domain, Heinrich Füssli, Detroit Institute of Arts

According to Wikipedia, this painting, called "The Nightmare" is in the permanent collection at the Detroit Institute of Arts.

There is a slightly different version of the painting (Der Nachtmahr, eng: The Nightmare) dated 1802, which can be seen in the Goethe House in Frankfurt.

Johann Heinrich Füssli was a painter from Switzerland who spent much of his life working as Henry Fuseli in England. The image was originally on a 2002 DVD from Directmedia Publishing GmbH.

Nachtmahr, or nightmare, a dream that is accompanied by negative emotions such as anxiety and panic.

Sleep is one of the most important patterns of behavior of both humans and animals, but we still don’t know why we sleep. Two and half centuries after Heraclites, sleep still remains one of the biggest unsolved mysteries of biology.

Sleep decreases our reaction to environmental stimuli, causes certain electrical brain signals, and can easily be ended — in contrast to fainting or hibernation. If we are prevented from sleeping, we develop a sleep deficit (link to Der Spiegel, German magazine), which we then try to eliminate as quickly as possible by sleeping more intensively and for longer periods of time. Since even scorpions, flies, and cockroaches have this sleep requirement, our need to sleep most likely developed more than a half a billion years ago.

But how did it develop? Most likely from the Circadian clock found in every living creature that links metabolism and behavior to the rotations of the earth. This internal clock is even found in simple bacteria and makes itself known whenever we fly through multiple time zones and end up being exhausted even if it is the middle of a sunny day.

2.1. The two control circuits

The core of our internal clock is a tightly packed bundle of nerves found deep in our brain where genes turn themselves on and off every 24.4 hours and in this way control the release of sleep hormones (melatonin and "somatotrop..") in the brain. This “central clock” ticks a little slower than the day-night cycle, but is reset daily to a new 24-hour cycle by light signals received by the eyes. Our internal clock ensures that we sleep at night and are active during the day.

How much sleep we need is regulated by a second control circuit, about which we know very little. It causes a newborn to sleep up to 17 hours a day, a six-year-old child from 9 to 11 hours, and an adult an average of 7 to 9 hours.

As we age, our need to sleep does not decrease; instead, our sleep is usually not as deep and we have regular periods of wakefulness.

As only about one in two adults in the Western world manages to get the sleep they need, there are many people who suffer from a chronic sleep deficit.

This impairs our ability to communicate, make decisions, and learn and also affects our hormone metabolism and the effectiveness of our immune system.

2.2. Sleep deprivation and sleep genes

Sleep deprivation impairs the precision of a bee’s waggle dance, which a bee does to show the other bees the direction to the food source. And sleep deprivation of two to three weeks is deadly for rats and flies; they develop wounds and are no longer able to metabolize their food. I do not know of any solid evidence which shows that sleep deprivation is also deadly for humans.

Excerpt from Wikipedia on sleep

Sleep is a state of external relaxation in both humans and animals. During sleep, many vital signs are very different from the state of wakefulness. The pulse, respiratory rate, and blood pressure sink in primates and higher organisms during NREM sleep, and brain activity changes.

Having our eyes closed and increased tenseness in the middle ear during NREM sleep supports this function. During REM sleep, also called “paradoxical sleep,” we go through certain states that are very similar to being awake, in particular, increased brain activity (we most frequently remember dreams from this phase) and an increase in the heart and respiratory rate as well as the blood pressure. The musculature is an exception to this “active sleep state” as it is blocked in REM sleep (sleep paralysis).

Sleeping cat baby, beige, male among other sleeping cats.© Public Domain, Watchduck, Wikipedia

The need to sleep differs substantially from person to person and may well be partially controlled by genes. Genetically identical twins have similar sleeping patterns and habits whereas this does not hold true for fraternal twins.

Redaction comment

See also twin studies and falsified studies conducted by psychologist Cyril Lodowic Burt (1883–1971). But the accusations against him that began in 1974 as the Burt Affair are controversial and have never been conclusively proven.

Only about 5 % of all people can do well in the long term on six hours of sleep. However, a few years ago researchers found a family in which the mother and daughter slept only 6.5 hours and the other family members the typical 8 hours. It turned out that the mother and daughter had a mutated gene, which the researchers called DEC2. When this gene variant was implanted in mice, it decreased their need to sleep.

Only about 5 % of all people can do well in the long term on six hours of sleep.

A gene related to the DEC2 gene is also found in fruit flies and is part of their internal clock. For this reason, researchers suspect that the control circuit for our need to sleep developed from our internal clock. Perhaps it was an advantage for our distant biological ancestors to be able to temporarily avoid the strict dictation of the internal clock, thanks to this new control circuit.

It is not only DEC2 that controls the sleep patterns of humans and animals; instead, it is very likely that there are dozens or even hundreds of such genes. Two of these influence the electrical transfer of signals in nerve cells in fruit flies. If these genes are changed or destroyed, the flies have less of a need to sleep or even suffer from insomnia.

2.3. The mysteries must still be revealed

The discovery of “sleep genes” did indeed slightly open the door to the mysteries of sleep, but it will most likely take some time until we are able to identify all of the genes involved in sleep and to understand their modes of action. However, science is patient; once it has its foot in the door, it doesn’t give up until it is able to open the door completely and reveal the well-guarded secrets.

Marine mammals and birds sleep with half of their brain awake. Whales and dolphins, for example, can then still swim to the surface to breath, even though they are sleeping, and some birds can likely sleep while they are flying. In doing so, these animals only open one eye, the eye associated with the side of the brain that is awake. Sleeping dolphins direct their gaze toward the middle of their pod, perhaps to prevent individual members from leaving and running into danger.

A Common Raccoon (Procyon lotor) seen near a bike path near Schererville, USA.© Public Domain, Dmytro S., Wikipedia
Dormancy should not be confused with hibernation. The following animals are dormant in winter: brown bears, raccoon dogs, raccoons, European badgers, some bats, and squirrels.

On the topic of internal clocks and chronobiology, see also Circadian rhythms, which drive our sleep-wake and day-night cycle. Our chronotype determines the times when we are most likely to sleep.

However, most animals sleep with both halves of their brain and as a result are more exposed to external risks. Why hasn’t evolution eradicated this dangerous behavior? Could it be that our brain replenishes its energy resources while we sleep? It is the organ that is most hungry for energy. Although it only makes up 2 % of our body weight, it uses 20 % of our body’s energy.

This explanation conflicts however with the fact that during the sleep phases in which we dream most often and our eyes move quickly behind our closed eyelids, our brain doesn’t use less energy, but in fact more. Another possibility is that our sleeping brain removes harmful metabolic products that accumulate when we are awake.

When we sleep, the distance between our brain cells increases, which could make it easier for the circulating spinal fluid to rinse the brain.

The most interesting explanation for our need to sleep is that our sleeping brain repeats and consolidates things we experience when we are awake. Trivial aspects are deleted and room for new memories is created. When we experience or learn something, the nerve cells in our brain form new connections and these are strengthened each time the experience or the new information is repeated.


If a rat learns to run through a maze, hundreds of nerve cells exchange electrical signals in a certain rhythm and in this way save the information about the path they learn. If the rat sleeps, the same nerve cells repeat the same dialog in the same rhythm, over and over — and sometimes much more quickly than when the rat was awake.

The next morning after having had a good night’s sleep, the rat remembers what it learned the day before and runs through the maze without any effort.

However, if the rat is woken up during the consolidation process, it forgets the path.

The outcomes of human studies are less clear, but they speak for the fact that sleep also allows our brain to either delete or permanently save the knowledge we acquired while we were awake.

2.4. Dreams, another mystery

And what about our dreams? From time immemorial, they have inspired our fantasy and even today they hold many mysteries.

Oil painting "The Dream of the Knight" by Antonio de Pereda (1611-1678) from ca. 1650.© Public Domain, Antonio de Pereda, Real Academia de Bellas Artes de San Fernando

The father of psychoanalysis, Sigmund Freud (1856–1939), saw in dreams our attempt to process unresolved experiences and desires (Sehnsucht). Perhaps dreams simply arise from random electrical nerve signals which simulate irrational and fantastical occurrences that the large part of our brain (cerebrum) then processes as well as it can into a coherent story.

Sleep is a place of refuge that we often long for when our life becomes difficult. And the no-man’s-land between waking and sleeping can reveal the world to us in a wondrous distortion and with unexpected connections. Will the darkness of these places of refuge soon have to give way to the bright light of science?

The pioneering sleep researcher William C. Dement doubts this: As far as I know, there is only one certain reason why we have to sleep: we get sleepy. The realm of sleep will certainly retain its mysterious darkness for a long time to come,

3. Editorial

This article appeared in the Neue Zürcher Zeitung (NZZ) in a slightly different version on August 24, 2015, on page 27 of the feuilleton section. The article was titled "Rätsel Schlaf" (The mysteries of sleep) with the subtitle "Nicht der Bruder des Todes" (Not the brother of death) instead of "Helfer des Lebens" (How this small death helps us live).

Dr. Gottfried Schatz, (1936–2015), emeritus professor at University of Basel was a biochemist. Wikipedia: Gottfried Schatz played a leading role in the study of the formation of mitochondria and is one of the individuals who discovered mitochondrial DNA. His realization that this DNA encodes for only a few proteins was crucial for his further research that dealt with the import of proteins into mitochondria and the breakdown of proteins within mitochondria.

You can read more about his work and books at the end of the article The Meaning of Life, Natural Science, and Belief in Religion. On, you can also read his article Epigenetics: We Influence Our Genes and the Genes of Others.

Shortly before publishing this version of his article, I was sad to learn that Gottfried Schatz had died on October 1, 2015, after suffering from a serious disease. When answering my follow-up questions about this article, he had mentioned that he was undergoing additional treatment that would hopefully give him a few more months to live.

4. Scientific studies on sleep

Dr. Chiara Cirelli of the University of Wisconsin in Madison, Wisconsin, is a neuroscientist who successfully researched and published on the topic of sleep starting in 2003. Dr. Cirelli, along with her long-term colleague Dr. Giulio Tononi, developed a comprehensive hypothesis about the function of sleep.

According to this hypothesis, sleep helps the brain renormalize synaptic strength acting as a counterbalance to the net "growing" of synaptic strength based on neuroplasticity that occurs when we are awake.

Dr. Cirelli developed a combination of molecular and genetic procedures and was able to identify hundreds of genes whose expression during sleep cause changes in neurons and glial cells.

In a second, complementary approach, she conducted a large-scale study and found several drosophila that have resistance against sleep deprivation. See also DNA profiling.

With her team, she conducted mice studies to examine how sleep and wake phases affect oligodendrocytes. In a healthy brain, these helper cells respond to damage by wrapping nerve axons with myelin. This is an insulating layer made up of fat and protein that allows for the quick transmission of signals. Thanks to the myelin sheath, the electrical impulses “hop” along the axons.

TRAP - innovative method to examine gene activity

Cirelli and her colleagues were able to examine the gene activity in previous defined cell types using their innovative method called TRAP. It was already known that as well as the sleep-wake cycle, the time of day can also have an effect on the gene expression of brain cells.

The team therefore used a control group of mice that they then kept awake during the usual sleeping periods. Simply putting a treadmill in the cage achieved this.

It was determined that in the oligodendrocytes of the sleeping mice, the genes responsible for the formation of myelin were turned on. This led the researchers to believe that the myelin sheaths are built up primarily during sleep.

In contrast, when the mice were awake, genes that are connected to cellular stress and cell death were active. See programmed cell death and apoptosis.

In addition, it was shown that during sleep twice as many of the precursor cells for oligodendrocytes came into being as during periods of wakefulness. Cells that later develop to become oligodendrocytes reproduce most productively during the REM sleep phase, which is when most of our dreams occur.

After just a few hours of sleep, the number of precursor cells (progenitor cells) increased. It had previously been assumed that this was a much longer process.

It was already known that the activities of neurons change during the sleep and wake phases. However, now we know that the way these helper cells work in our nervous system varies during the course of the sleep phases.

Dr. Cirelli also saw that chronic sleep deprivation can worsen multiple sclerosis syndromes (MS or encephalomyelitis disseminata, ED). In MS, the body’s own immune system attacks the myelin sheath of neurons in the brain and spinal cord, which can lead to a number of neurological disorders. A connection in MS patients between sleep and the severity of their symptoms has not yet been confirmed.

It would be interesting to know whether or not disease mongering can, in a manner of speaking, steal a person’s sleep, This would then be a vicious circle, which in any case would cause poor sleep.


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