Why We Sleep

Summary of “Why We Sleep”: Matthew Walker, professor of neuroscience and psychology as well as director of the Sleep and Neuroimaging Lab at UC Berkeley unveils all the mysteries that surround sleep.

By Matthew Walker, 2017, 368 pages Note: this is a guest review written by David Jedresac of the blog Apprendre Retenir Agir (“Learn Remember Act”)

Review and summary of the book Why We Sleep

Part 1. What is sleep?

In today’s society, many of us sleep less than we should. Are you personally getting enough sleep? Two-thirds of adults in developed countries do not get eight hours of sleep. This may not come a a surprise, however, the consequences may. Matthew Walker wastes no time in getting right to the heart of the matter. The book is meant to be informative, but Matthew’s mission is to get us to sleep more and better. Not getting enough sleep destroys your immune system and increases your risk of cancer. Your chances of getting Alzheimer’s increase drastically.

Lack of sleep makes you vulnerable to cardiovascular disease, stroke, and congestive heart failure. Many psychiatric illnesses are made worse by lack of sleep, including depression, anxiety, and suicidal ideation. It also increases the risk of obesity. Your whole understanding of sleep will change when you read the book. We might think that the 3 pillars of good health would be diet, exercise, and sleep. According to Matthew, this is partly wrong, sleep is more than a pillar, it is a foundation on which the other two are built.

1.1 Circadian rhythm

The circadian rhythm is defined by a hormone called “melatonin“. When this hormone increases, the desire to sleep increases. Melatonin is subject to certain external elements. These include the sun, age, and DNA. Each person’s rhythm is different. This is why we speak of “early sleepers” or “late sleepers”. So, for some people, the peak of melatonin occurs early in the evening and then decreases early at dawn.

The “early sleepers” represent 40% of the population. The “late sleepers” represent 30% of the people, they go to bed late and get up late, sometimes in the afternoon. The last 30 percent are in between. Failure to respect your rhythm will cause your brain to malfunction. In fact, it will not be functional until it reaches its rhythm. For example, if you are a night owl and go to bed at 8 p.m., chances are that by 4 a.m. your prefrontal cortex will not be functioning properly. Like a cold engine. This is due to the genetic code, your DNA. Melatonin, however, has no influence on sleep, it just triggers it.

In other words, melatonin does not contribute to sleep itself, it simply initiates it. With time differences, the circadian rhythm is put to the test. The author explains that when he travels, he has to deal with this particularly painful time difference. For example, a flight from San Francisco to England. There is an 8-hour difference between London and California. So, when it’s midnight in London, it’s only 4 pm in California. Falling asleep will not happen until eight o’clock in the morning, when everyone is waking up. The body eventually gets used to it, but the process is slow. Each day, the suprachiasmatic nucleus (the 24-hour biological clock located in the heart of your brain) readjusts itself by a single hour. It will therefore take 8 days for the rhythm to be in sync with the location.

1.2 Caffeine

Sleep is defined by two factors. As we have seen before: the circadian rhythm is one of them. There is a second. Adenosine is the second factor, it is a neurotransmitter independent of melatonin. Adenosine, unlike melatonin, keeps increasing throughout the day. If you have an all-nighter, adenosine will be very high. However, in the morning, even if you didn’t sleep at night, you may be reasonably alert, thanks to fairly low melatonin (which is regulated by your circadian rhythm). Adenosine is placed on receptors in the brain to signal that we are tired.

The role of the stimulant caffeine is to block receptors. Rather than giving the signal to fall asleep as adenosine does, caffeine stimulates that part.  Adenosine can no longer play its role, and we will not feel sleepy for a while. Caffeine usually takes effect 30 minutes after ingestion. It takes 5-7 hours to reach half-life. The half-life is the fact that caffeine still has 50% of its effects on the body. It is therefore important to take this into account before going to sleep. Having a coffee with your evening meal seems like a bad idea. Indeed, if you take a coffee at 7 pm, the caffeine will still be 50% active at 2 am (which is still considerable).

Caffeine is evacuated from the body by an enzyme in the liver, which is more or less effective in different individuals. This is what makes caffeine more or less stimulating for some people. This stimulant, the most consumed in the world, is found in coffee (even decaffeinated), tea, coca, and some dark chocolates.

1.3 The sleep cycle

While we sleep, the brain follows a distinct pattern each time. The sleep cycle is very clear and has been clearly identified, we see that it follows phases. During certain phases, the eyes are in motion, they move from one side to the other furtively. The brain waves are then active almost like in the waking state. Then, in other phases, the eyes become quiet and still. The waves are then slowed down. These phases are repeated every 90 minutes. This is REM sleep (Rapid Eyes Movement). Then, NREM sleep (No Rapid Eyes Movement), which is deep sleep. Deep sleep has 4 levels of depth. During the cycle, the brain follows 5 almost identical phases of 90 minutes. This means that we need 7.5 hours of sleep, which we round up to 8 hours to be sure that the sleep cycle is completed.

How sleep cycles work

In this diagram, we see that the phases are quite different, and this difference is very important. In the first three cycles, sleep is mostly deep and then REM sleep takes over. Deep sleep and REM sleep have two distinct roles, and we will see throughout this summary the role of both. In any case, you should know that missing 2 hours of sleep out of 8 makes you lose about 65% of REM sleep. This means that your sleep is significantly lacking with just 2 hours less sleep.

1.4 Who sleeps?

When did sleep appear in evolution? The answer is simple, sleep has always existed. One of Matthew’s theories is that sleep was present from the beginning and that it is wakefulness that is “anomalous”. This means that sleep repairs the energy we use when we are awake. Who sleeps? Which species? All of them, without exception. Even insects. We can’t analyze the brain waves of insects. However, researchers have been able to ascertain through their behavior that they require sleep. Sleep is different in all species. For example, it seems that most fish, insects, and reptiles do not have REM sleep (dream phase). In any case, at the moment researchers have not been able to prove it.

It is possible, however, that they do have a dream phase that is simply different from ours, undetectable with current technology. Bats sleep 19 hours and elephants only 4 hours. Why do we have such different sleep needs? We don’t really know; the complexity of the brain and the size of the body certainly play a role. Nevertheless, all living species sleep in their own way, in ways that are suitable for them. For example, during REM sleep, the body is paralyzed and cannot move. In humans, this function is to avoid replicating what we dream about in our beds (rather practical). For dolphins, this phase is hardly possible, because they constantly need to swim in order not to be carried away by the current and lose control completely. This is why they only have an NREM (deep) phase.

Another difference between animals and us

Another difference between species and us humans is the resting of one part of the brain. We have two hemispheres in our brain and some species are able to rest one of them while leaving the other one working. As each species has evolved differently, so have its needs. This is particularly true for birds. During a flock of birds, you can be sure that most of the birds are sleeping. Only the two birds at the ends sleep with only one hemisphere. This is to monitor the environment while they are sleeping.

This is also the case for dolphins for the same reasons mentioned above. Humans are not able to do this. Instead, we seem to have a similar, but much less efficient variation. When we first sleep in a new environment, we maintain a certain level of alertness; for example, during the first night in a hotel. However, we still rest both hemispheres at the same time, unlike species that are able to alternate.

We are special

Matthew outlines his evolutionary theory, which is very interesting. REM sleep serves in part to regulate emotions and improve our problem-solving ability (explained in detail in Part 3). At the time of Homo Erectus (predecessors of Homo Sapiens), they had mostly NREM sleep, as most species slept in tree branches to avoid predators. However, REM sleep paralyzes the body, so Mother Nature could not grant it to them in order to protect them from fatal falls during sleep. In the course of evolution, Homo Erectus (and thus, Homo Sapiens) discovered fire and thus could sleep on the ground.

Naturally, REM sleep came in very large quantities. Given the benefits of REM sleep, it is possible that this is what made Homo Erectus progress so much in terms of intelligence. Moreover, since REM sleep allows the management of emotions, it is also what made human beings evolve as deeply social beings. The evolution of sleep could therefore explain why Homo Erectus ended up becoming what we are today. It is safe to say that we have the most elaborate sleep of any species.

1.5 Chronology of sleep

The fetus

Even when we are in the womb, we sleep a lot. This is the period when we sleep the most in our entire existence. In a 24-hour period, the fetus consumes 6 hours of NREM sleep, 6 hours of REM sleep, and 12 hours of intermediate sleep. It is only in the last trimester of pregnancy that the fetus experiences its first state of wakefulness. However, this is only 2 to 3 hours per day. When the baby moves in the womb, it is in REM sleep. Although the baby is certainly not dreaming as we do.

Note that the REM sleep paralysis that we experience is not yet active in the fetus. The extra fetal REM sleep allows for normal brain development. Synaptogenesis is a phase that involves the creation of millions of connections between neurons called “synapses”. In other words, this is the phase where the mainframe computer is installed. In fact, it is largely REM sleep that makes this possible.

Note that if we block REM sleep, the neuronal connections are completely disrupted. The consumption of alcohol blocks REM sleep. Moreover, and unfortunately, a pregnant woman who drinks alcohol causes the fetus to lose REM sleep, which is essential for its development. Drinking alcohol while breastfeeding has the same effect. The brain has no notion of debt, and lost REM sleep hours are never recovered.

The child

Unlike adults, a child’s sleep is polyphasic. It is fragmented during the day and night. It is necessary to wait between 3 and 4 months for the suprachiasmatic nucleus (which handles the circadian rhythm) to develop into biphasic sleep. At the age of one year that the suprachiasmatic nucleus adopts the circadian rhythm. Finally, at the end of adolescence, the modern monophasic pattern is established. NREM sleep dominates the childhood period.

The adolescent

This is where things get complicated. We often believe that a 16 year-old “must” go to bed early in order to get up early (given the start time of classes, taking into account the travel time and the preparation time before heading out). This is biologically unnatural. The circadian rhythm of a teenager is very delayed unlike an adult. Where an adult begins to show signs of fatigue at 10:00 pm / 11:00 pm, the teenager has a peak of wakefulness.

It is only a few hours later that he will have a rise in melatonin. This is rather inconvenient, considering parents would like their teenagers to go to bed at 9 p.m. so they feel well rested in the morning before heading off to school. Let’s look at it the other way around. It’s the school start time that is problematic, not the teen’s circadian rhythm. Telling a teenager to “go to bed at 10 p.m. and be up and running by 6 a.m.” is like telling an adult to “go to bed at 7 p.m. and be up and running by 3 a.m. At this time, sleep is still essentially REM sleep. The brain continues to evolve, shedding some connections to make new ones.

This means learning and retaining new things. The maturation pathway ends at the tip of the frontal lobe, which is the home of rational thinking and critical decision-making. This is why adolescents often have difficulty making decisions and often misjudge danger. Depriving a teenager of NREM sleep increases the chances of psychiatric disorders, such as schizophrenia, bipolar disorder, depression, attention disorders, etc.

People in their 40s and older

The elderly need as much sleep as adults. However, they generally get much less sleep than adults. This is due to the fact that the brain atrophies unevenly. Unfortunately, the first part to deteriorate is the middle frontal area above the bridge of the nose, which is responsible for deep sleep. This leads to a very sharp decrease in NREM sleep. The loss of sleep, therefore, does a lot of damage to the brain. Just as if we deprive an adult of sleep, an elderly person has an increased risk of diseases, including Alzheimer’s disease (more on this later).

Often, health problems in the elderly can be related to lack of sleep, something that doctors or family members may not be aware of. The rhythm of the elderly is much more similar to that of adults. Melatonin tends to come earlier. The elderly are therefore more likely to be early risers. Their sleep is also more fragmented due to the need to go to the bathroom during the night as well as other factors.

Part 2. Why do we sleep?

At the beginning of this part, Matthew Walker announces a new exceptional treatment. This treatment would extend your lifespan, reinforce memory and creativity, make you more attractive, help you stay slim and avoid snacking. It would prevent cancer, and dementia and would repel colds as well as the flu. On top of all that, it would decrease the risks of having a heart attack, a stroke, and even diabetes. And that’s not all, it could make you happier, less depressed, and less anxious. Of course, he is talking about a good night’s sleep.

2.1 The benefits of sleep

One of the most important benefits of sleep is learning. Learning and retaining information are linked to good sleep. A part of the brain called the hippocampus enables us to store information but in a very limited way. Like remembering where we left our car keys, for example, it is the hippocampus that is in charge. Then the information is transferred to the cortex, which is actually long-term memory. The author’s research team conducted a test to prove this theory.

He had two groups of young adults, one taking naps, the other not. At noon, the participants had to remember 100 pairs of faces and names to test their short-term memory (the hippocampus). Shortly thereafter, the napping group took a nap, and the other group did something else but did not sleep. At 6 o’clock in the evening on the same day, another learning experience happens again. The nap group had a better memorization result (by 20%), and the other group had, however, stable concentration. The NREM sleep allowed the hippocampus to be flushed out during the nap, thus restoring learning capacity. This means that sleeping well prepares you to learn well.

Sleeping after learning

After learning, good quality sleep is like pushing he “save” button. A phenomenon called “consolidation” protects the new data. In 1924, two German researchers by the name of John Jenkins and Karl Dallenbach compared the learning capacity between sleep and wakefulness. Participants began by retaining facts that were stated orally. After 8 hours, the goal was to have one group awake and the other that had spent the night sleeping. The result was clear: those who slept consolidated the information. Those who stayed awake had fuzzy recall [1].

Many other kinds of research have been done since, and we now understand how sleeping enables us to “remember”. During NREM sleep, waves travel back and forth between the hippocampus and the neocortex at the top of the brain. The hippocampus stores short-term memories. The neocortex, on the other hand, is in charge of long-term or even lifelong memories. So, the brain sends a messenger who takes care of the transfers between the hippocampus and neocortex during deep sleep.

Memories are selected

NREM sleep does not transfer all the content learned from the hippocampus into the neocortex, it selects what its owner wants to keep. When you pay attention to a piece of information, you are likely to retain it after sleep in your long-term memory. However, if you learn something you are not interested in, you are likely to forget it. For example, gossip from your neighbor may not interest you; NREM sleep has the intelligence to sort it out for you. On the contrary, if you are learning a language, it will make more effort to retain it provided you devote enough attention and consistency to it.

Increasing motor skills

Sleeping reconfigures neural connections. This makes it possible to improve by practicing. Matthiew Walker crossed paths with a pianist in 2000 when we did not yet know as much about sleep, following a conference. The pianist said to him, [Sometimes when I insist on learning a particular piece, I can’t master it. Then in the morning, after I’ve slept, I can play it perfectly.] A sudden light bulb went off in Matthew, and he decided to pursue this theory. A good decade later, there is no doubt.

It is by practicing and sleeping that one reaches perfection. Whether it’s piano, basketball, tennis, flying an airplane, surgical procedures, etc., improvements come during the night, not during the practice itself. It is the last two hours of sleep that allow this to happen, as this is when brain wave surges related to reinforcement are most present. NREM sleep does not only allow good memorization, it allows you to become an Olympic champion. We also know today that neuronal reconnections following a stroke take place during sleep. Day after day, stroke patients have new connections formed, which allow a certain level of damaged areas to recover. This gradual recovery determines the relearning of many faculties. [2]

2.2 Lack of sleep

This part is not the most pleasant to read, but it is one of the most interesting. Let’s focus on the consequences of sleep deprivation. Sleep deprivation has been deemed too extreme to appear in the Guinness Book of World Records. In fact, the records accept a man climbing into a hot air balloon at an altitude of 39,000 meters and then free-falling at 1,358 km/h at top speed breaking the sound barrier.

Sleep deprivation is considered worse than that. Lack of sleep, even if mild, causes us to lose concentration. There can be many consequences to this. One of them is traffic accidents. Just after ten days of 6 hours of sleep per night, performance is reduced as much as after 24 hours without sleep; that is, a 400% increase in microsleeps (very brief loss of consciousness), which can easily prove to be fatal in a car driven at 50 or 100 km/h.

We don’t realize that we are sleep deprived

We are very bad at judging our state of fatigue. A person who gets a few consecutive, short nights of sleep may think he is fine. However, he has just gotten used to his state of fatigue, but he actually has much slower reflexes and diminished concentration and potentially micro-naps. Fatigue is responsible for 1.2 million accidents each year in the United States. After 3 decades of research, we know the recycling rate of a human. After 16 hours of wakefulness, the brain begins to malfunction. We need more than 7 hours of sleep to preserve our cognitive performance.

Seven nights of 7 hours of sleep makes the brain malfunction as much as one sleepless night. 3 full nights of sleep (knowing that it is less than what a weekend includes) is not enough to catch up. Lastly, humans cannot recognize how much sleep they are lacking. The author also gives a point of attention to tired drivers that I share in this summary. If you are dosing off at the wheel, please pull over. This is life-threatening and can lead to other people dying. If you feel drowsy or are, God forbid, falling asleep, stop for the night. If, however, you decide to continue anyway, pull off the road at a safe parking area and take a quick nap (20 to 30 minutes). Do not drive immediately to avoid sleep inertia.

Wait another 20 to 30 minutes and even have a cup of coffee if you wish. After that, get back behind the wheel, but the rebound will only be for a short time, so it’s not really worth it. It’s best to stop completely and get a full night’s sleep.  It’s better to stop when you still can, rather than wait until it’s too late.

Is napping useful?

Napping does indeed allow for a concentration rebound. However, it is short-lived and is not as effective as a good night’s sleep. It can be helpful when we are sleep deprived. However, no drug, no caffeine, no nap can replace the complex functions of the brain. If you want the many and varied benefits of sleep, you have to… well, sleep. Napping is still a useful supplement to good sleep. There is, however, one exception. People with a subtype of the gene called BHLHE41 (also called DEC2) may naturally sleep less. In fact, they sleep only six hours and no more, even when they have the opportunity to sleep more. This gene is extremely rare, there is more chance of being struck by lightning (1 in 12,000) than having this gene. So, it is very unlikely that you have it.

Disturbed emotion

Through the use of MRI, research found that the amygdala, the key location where emotions are triggered, had an increase by lack of sleep, up to 60%.  We can see the amygdala as a gas pedal and the prefrontal cortex as the brake (the prefrontal cortex governs willpower, among other things). The amygdala helps regulate emotions. Lack of sleep upsets the balance between the two, making negative emotions much more problematic. Furthermore, an area behind the amygdala called the “striatum” (impulsivity and satisfaction center) is bathed in the chemical dopamine and becomes hyperactive in sleep-deprived people. In other words, sleep-deprived people will be highly receptive to immediate pleasures, which is directly related to procrastination, in addition to being emotionally out of whack, especially with regard to negative emotions. [3]

Alzheimer’s disease

People who sleep little during their adult life increase their chances of developing Alzheimer’s disease. This is due to the deposition of a toxic protein called “amyloid beta“. This protein attacks the neurons in a targeted way. The area that is attacked is the frontal lobe, which is responsible for NREM sleep. Unfortunately, it is NREM sleep that enables new memories to be made, and amyloid destroys NREM sleep.

To dispose of this toxin, the brain deals with it during neural cleaning. This is done during NREM sleep. How does it work? The size of the brain’s glial cells sometimes decreases by 60% during NREM sleep. This allows the cerebrospinal fluid to efficiently clean up the metabolic waste left over from the day’s neuronal activity. Amyloid deposits are therefore flushed out during neuronal cleaning [4].

2.3 Cancer, heart attacks, and shortened lifespan

Concerning heart attacks, lack of sleep again has a major impact, in addition to bills, tobacco, alcohol, etc. Lack of sleep increases the time your body activates its sympathetic system. The sympathetic system (a rather misleading name) is the “fight or flight” system that your brain activates when faced with danger. It activates the stress hormone cortisol, increases blood pressure and heart rate [5]. Your sleep-deprived heart beats faster and the blood pumping through your vascular system increases as does your blood pressure. In addition, growth hormone, which is released at night, is stopped by lack of sleep, despite the fact that it replenishes the walls of our blood vessels. This chain of consequences increases heart attacks. Incidentally, during daylight saving time in the northern hemisphere, there is an increase in heart attacks the following day due to the fact that we sleep one hour less because of the time change.

Risk of obesity

Lack of sleep also increases the risk of obesity. The cause is due to hormones that are related to food, in particular, the hormone ghrelin, which makes you feel hungry, and leptin, which makes you feel full. Both hormones are disrupted with a lack of sleep. Ghrelin increases, which makes us feel hungrier when we are not, and leptin decreases, no longer properly signaling that we are full. In addition, there is an increase in endocannabinoids, which stimulate appetite and increase the urge to snack. This is a particularly detailed part of the book; however, there are no references.

Decreased testosterone

Sleeping less makes us become less attractive and on top of that, we find other people less attractive. The testosterone levels in men dip. As a result, they become more tired and less concentrated. They also have a lower libido, making it difficult to have an active, fulfilling, and healthy sex life. In women, sleeping 6 hours a night causes a 20% decrease in the follicle development hormone that is essential for female reproduction. The chances of getting pregnant are therefore reduced.

Reduced immune system

Recent studies conducted by Dr. David Gozal of the University of Chicago show that lack of sleep amplifies cancers. Tests were produced on mice that were injected with malignant cells. The sleep deprived mice suffered a 200% increase in the growth rate and size of the cancerous tumor. Immune system cells called “macrophages” are one of the root causes of how sleep loss affects cancer. The M1 cells that fight cancer decrease. On the other hand, M2 cells increase due to lack of sleep, which increases the growth of tumors. The combination of the two explains the growth of tumors in the mice that experienced it. The World Health Organization has classified night work as ” possibly carcinogenic “.

Part 3. Why do we dream?

Why do we dream?

Even today, we do not know exactly the function of dreams. There is no study with sufficient evidence to demonstrate it. However, our knowledge of dreams has improved considerably. Thanks to MRI, we know how the brain reacts during REM sleep (i.e., during the paradoxical phase, which is when dreams occur). When you start dreaming, 4 main brain regions are activated: 1 – visuospatial regions, located at the back of the brain, which are responsible for complex visual perception; 2 – the motor cortex, which is responsible for movement; 3 – the hippocampus and the ones next to it, which preserve your autobiographical memory; 4 – the deep emotional centers of the brain, the amygdala and the cingulate cortex.

The meaning of dreams is not yet fully understood. What is certain is that Freud’s theory in the past was wrong. Freud’s theory in 1899 was that dreams were repressed desires of the day that went unfulfilled, which Robert Stickgold of Harvard University proved to be false. He asked 29 adults to keep a detailed logbook for two weeks. In 299 descriptions obtained, only 1% to 2% of the events while awake occur in dreams. Therefore, it is not a rerun of when you were awake. We should kindly embrace dreams as they happen.

3.1 Nocturnal therapy

During REM sleep, the concentration of noradrenaline is nonexistent. Norepinephrine is a stress-related substance. Over 24 hours, the amount of norepinephrine is lowest during REM sleep. Matthew hypothesized about dreams. REM sleep could reduce the visceral and painful emotional charge attached to painful memories. A true night-time therapy. To put this theory to the test, Matthew gathered two groups. The goal was to show emotional images at two times of the day. Group A saw the images in the morning and then 12 hours later in the evening. Group B saw the images in the evening and then, 12 hours after a night’s sleep, in the morning. Both groups were emotional upon first viewing.

Upon the second viewing, Group A had a deep and negative emotional reaction, if not more so than the first viewing, and they reported feeling the same painful feelings with equal intensity. Group B, who had slept through both sessions, reported a characteristic decrease in the degree of emotion when they viewed the images a second time. MRI images showed a significant reduction in reactivity in the amygdala, the emotional center. To be effective in this dream therapy, one must dream about the experience in question, it is not enough to be in REM sleep.

Post-traumatic stress disorders

One specific area that is not subject to this rule is post-traumatic stress disorder. These people present with a condition that the brain is unable to cope with. War veterans often suffer from this type of disorder. A soldier who experiences this often has the same nightmare over and over. The amount of norepinephrine is particularly high in the brain, which is a dysfunction as we saw earlier. Matthew met Dr. Murray Raskind, who was working in a VA hospital, following a publication of his research on dreams.

Raskind told him that some combatants had been cured of their nightmares by taking a drug called prazosin. The utility of this drug is to lower blood pressure. However, it has a side effect of suppressing norepinephrine during REM sleep. The brain seems to want to process an emotion until it gets its way. Since the trauma is too high in post-traumatic stress, the brain insists. After taking prazosin, veterans had their emotions successfully processed. There are still many questions to be answered about this as treatment is still incomplete, but this is a great first step in treating post-traumatic stress disorder.

Deciphering experience

When we lack REM sleep, we perceive the outside world as more threatening. Matthew did an experiment, showing faces with different expressions. People lacking REM sleep were not able to accurately distinguish between emotions. The compass for emotional navigation via telltale cues on others’ faces lost its sensitivity north. As a result, participants in the experiment saw people with friendly, pleasant expressions as threatening. Some participants literally suppressed their sensible ability to read the social world around them. Matthew thinks of the police, military, doctors, nurses, emergency services, and security guards who are directly affected by this because if they are sleep deprived, it would mean that they are no longer able to properly assess a given situation.

3.2 Creativity

It is during REM sleep, i.e. the time when we dream, that creative power is at work. Many artists have been able to take advantage of the power of dreams to accomplish their work. This is the case of Paul McCartney with the songs Yesterday and Let it Be, Keith Richards of the Rolling Stones with the introduction to Satisfaction (discovering in the morning with amazement his creation without realizing it!) or Dimitri Mendeleev whose dream was the periodic table of elements. The brain employs associations to be logically conscious. It associates memories from the whole bank during REM sleep to make dreams. Matthew conducted an interesting experiment on patients.

They were awakened 4 times in the middle of the night. Twice at the beginning of the night, once during REM sleep and once during NREM sleep. Then, a second time at the end of the night and as before, once during REM sleep and once during NREM sleep. Patients found themselves more creative while in sleep inertia (awake, but still somewhat asleep). Not only that, but they were also much better at solving problems.

Problem solving

As we saw earlier, the brain works by association. Semantic knowledge is like a pyramidal family tree, which is a bit like mind maps. Robert Stickgold did an experiment similar to Matthew’s. When subjects wake up during REM sleep, the brain ignores associations, the brain creates shortcuts without hierarchy, with obvious links, favoring connections between distant concepts. Unlike when the experimental subjects were awake during NREM sleep, the dreaming subjects had a much higher problem-solving ability. In the waking state when we try to be creative, it is as if we are looking through the wrong lens. When we dream, we have the wide-angle lens of the dream, being able to measure all the information stored and the combinatorial possibilities for outstanding creativity.

Lucid dreams

Science has proven that lucid dreams are possible. People who mastered lucid dreaming could be tested. They were able to communicate with the examiners with their eye movements. Let’s not forget that during REM sleep, the body is paralyzed, except for the eyes (Rapid Eyes Movement). We don’t know yet if lucid dreaming is beneficial or not. This may be the next evolution of sleep in human beings because voluntarily controlling the benefits of REM sleep would be very interesting. However, the jury is still out on this.

Part 4. Improving sleep

Here the author discusses the most significant sleep-related problems. Starting with sleepwalking. Sleepwalking disorder refers to sleep disorders involving movement. It occurs during NREM sleep (i.e. during the non-dreaming phase). Insomnia is having trouble sleeping. It is not to be confused with not allowing yourself time to sleep or not respecting your circadian rhythm. Insomnia is a real sleep disorder, and if it lasts, it is better to consult a sleep specialist without taking sleeping pills (we will see why next). For narcolepsy, the first symptom is daytime hypersomnolence which represents sleep attacks during the day.

The second symptom is waking up with paralysis of the body, the impossibility of speaking or moving which is particularly unpleasant and even frightening. It is actually the paralysis of REM sleep that is abnormally prolonged during the awakening. And the worst for last, the fatal family insomnia. I got chills while reading this passage. This is caused by an unwanted version of the prion proteins (which have a very useful function originally). These abnormal proteins attack the thalamus, responsible for sleep, making it like Swiss cheese according to autopsies.

This results in… complete inability to sleep until death. Michael Corke was a 40-year-old devoted husband and music teacher at a high school in New Lexon, south of Chicago. He began having trouble falling asleep until he couldn’t fall asleep at all. After six months of not sleeping, he was bedridden and despite his young age his neurological condition was that of a senior citizen in the final stages of senile dementia. He died a few months later at the age of 42. There is no known treatment for this disease. Did I not say it was bone-chilling?

4.1 What keeps us awake

Artificial light

The artificial light we have in our homes today prevents the production of melatonin. Matthew recommends limiting artificial light before going to bed. Especially the light from phone screens or screens in general that emit blue light. The “yellow light” or “eye comfort shield” option on some screens can alleviate this problem.


Drinking alcohol has two consequences. The first is fragmenting sleep. The second is suppressing REM sleep and its benefits. I personally thought that alcohol helped me sleep, because I did, but it is true that I dream much less after a night of drinking. That being said, drinking alcohol causes one to lose a lot of problem-solving ability as well as creativity as we have seen. The author has no specific advice other than to drink alcohol in the morning (which almost no one does) or not drink at all. Unfortunately, the effects on learning are such that even after several days, information is not crystallized in the brain. For that, you need a full night of quality sleep [6].

Body temperature

Room temperature is very important because it affects your body heat. The human body is made to lose body temperature at night, because if we sleep outside, we would be subject to the natural temperature drop of the planet. It is the heating of houses that has disturbed this. The ideal temperature is precisely 18.3 degrees Celsius. Between 15 and 19 degrees Celsius will do the trick. The temperature should not be too low, but especially not too high. This temperature is calculated taking into account standard sheets and pyjamas.

4.2 Why not take sleeping pills

Matthew Walker strongly advises against taking sleeping pills. Sleeping pills do not improve sleep, quite the opposite. All sleeping pills act as sedatives in the same way as alcohol. They make it easier to fall asleep, but deteriorate the quality of sleep itself. A team of doctors examined all the studies published to date on modern sleeping pills. [7] The conclusion of this study was that the effectiveness of sleeping pills was considered dubious. The benefits are small or nonexistent. The learning capacity that sleep allows is therefore greatly reduced when taking sleeping pills since sleep is degraded.

The profits of pharmacies

Moreover, the profits made by “Big Pharma” as Matthew says, are staggering. Ambien, one of the sleeping pills, brought in 4 billion dollars in only 24 months. One could understand why they are still widely used (and wrongly). Unfortunately, no sleeping pill is really effective today, only natural methods will allow you to enjoy the benefits of sleep.

Try this instead

Matthew advises cognitive behavioral therapy for insomnia (CBTi) to get better sleep. Here’s everything you need to do to implement the method:

  • Caffeine and alcohol reduction
  • Remove screens from the bedroom
  • Establish a regular bedtime schedule, including weekends
  • Go to bed only when you start to fall asleep and avoid the couch in the early or middle of the evening
  • Do not stay in bed for a significant period of time
  • Avoid daytime naps if you have trouble sleeping at night
  • Reduce anxiety-producing thoughts and worries by practicing mental deceleration
  • Eliminate visible clocks in the room

Exercise also helps with falling asleep but should be avoided at least 2 hours before going to bed. You can also find advice on the National Library of Medicine website.

4.3 Why society is wrong

In our modern society, we have very little respect for sleep. It is the same for many countries and many companies. This is not the case for NASA or Google who take sleep seriously. Not only to please employees but because healthy sleep increases productivity. Studies have been done to prove that poor sleep leads to a lower work rate and a lower speed of accomplishment of basic tasks. Employees also find fewer and less appropriate solutions to problems encountered at work. [8] This is in addition to the fact that sleep deprivation also makes people less honest and lazier. This whole chain of causal effects makes companies less efficient and less enjoyable to work in.

The author then goes on to talk about schools that start far too early. As we saw earlier, 16 year-olds have a circadian rhythm that is 2 to 3 hours earlier than adults. Making them wake up at 5 or 6 o’clock for those who take the bus early is very counterproductive. This is because sleep allows for learning and memorization. This is clearly not an optimal model, even in France. The same is true for doctors. During their extensive studies, future doctors generally get little sleep. They are therefore likely to associate this with little importance towards sleep. Consider the case of a physician who has slept poorly at night. No matter how much knowledge or experience they have, they will potentially make more mistakes. This has a direct impact on the people who need care.

4.4 A new understanding of sleep

In this section, Matthew Walker outlines his views on improving the system. It’s a bit of an idealistic vision that is ambitious, but, effectively, we need it. It concerns the change of bulbs for less harsh lights that would favor natural melatonin, customized adaptive heaters, changes of habits as well as a drastic societal change that puts more emphasis on sleep. As we have seen before, starting school later, flexibility of working hours for workdays. Naturally, the major obstacle is the perception that we have about sleep and the fact that we tend to underestimate its importance. Sleep is indeed essential and should in no way be neglected.

For information on sleep, you can visit this site: https://www/sleepfoundationg.org

Conclusion on Why We Sleep by Matthew Walker

Considering that the book is extremely dense in terms of scientific and non-scientific information, it is difficult to take and adapt the information. The best conclusion I can draw that may resonate with you is to take your sleep seriously once and for all. You have seen all the many benefits, such as learning, memorization, creativity, problem solvinghealthy management of emotions among other benefits, but also everything that a lack of sleep causes. Would you like to potentially get Alzheimer’s disease just because you neglected your sleep? Matthew Walker has done a tremendous amount of work for this book and demonstrates the facts about the need for sleep. The brain is much more than a computer as it works even when we sleep.

For this work to be effective, we must respect it, out of respect for ourselves. The question to ask yourself is, after reading this summary, are you going to value your sleep? For my part, I have gained a newfound respect for my sleep after reading this book. I now even look forward to sleep because of all the daily benefits that I reap from it. I am more productive, more zen, more creative (significantly more), I have a better memory, and I have an overall feeling of well-being. With a full-time salaried job as well as a blog project in my “spare time”, I manage to hit my 8 hours almost every day, with occasional insomnia, I admit.

What helps me the most is going to bed at almost the same time every day and getting up at the same time. I do this despite my job requiring me to get up at 4 a.m. I strongly encourage you to value your sleep, your whole body will thank you for it. And I recommend this book if you wish to take an even deeper look at the science behind sleep.

David Jedresac from the blog Apprendre Retenir Agir (“Learn Remember Act”)

Strong points:

  • Extremely exhaustive in its subject matter
  • Numerous evidence-based studies
  • Includes all the compelling reasons to value sleep

Weak points:

  • Complex scientific terms
  • Key points should be addressed earlier on in the book

My rating : Why We Sleep by Matthew Walker Why We Sleep by Matthew Walker Why We Sleep by Matthew WalkerWhy We Sleep by Matthew WalkerWhy We Sleep by Matthew WalkerWhy We Sleep by Matthew WalkerWhy We Sleep by Matthew WalkerWhy We Sleep by Matthew WalkerWhy We Sleep by Matthew Walker

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Read more reviews on Amazon about “Why We Sleep”

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A handy little guide to the book, Why We Sleep by Matthew Walker.

The 4 main parts of the book:

  1. What is sleep?
  2. Why do we sleep?
  3. Why do we dream?
  4. Improving sleep

Frequently Asked Questions (FAQs) about Why We Sleep

1. How has Matthew Walker’s book Why We Sleep been received by the public?

The book has been a great success with readers and has made Walker famous in his field of expertise. The book became an international bestseller, including a No. 1 Sunday Times bestseller in the United Kingdom and a No. 8 New York Times bestseller.  It has been published in Spanish by Paidós and in traditional Mandarin Chinese by Commonwealth Publishing Group.

2. What has been the impact of Matthew Walker’s book Why We Sleep?

This book has helped the average person to understand the benefits of sleep and the importance of sleep, to develop a high regard for sleep, and also to understand the consequences of not getting enough sleep.

3. For whom is the book Why We Sleep intended?

If you’re a human being, this book is for you.

4. What is sleep according to Matthew Walker?

In his book, Matthew Walker states that he believes that sleep is not a switch, but a resting routine for the brain and body.

5. How does lack of sleep impact humans according to Matthew Walker?

According to the author, even a mild lack of sleep leads to a loss of concentration. There can be many drastic consequences to this.

The benefits of sleep versus the harms of insomnia

The benefits of sleep The harms of insomnia
Strengthens the immune system Destroys the immune system
Keeps us attentive and alert Undermines our attention and alertness
Makes us creative and boosts our imagination Reduces our ability to feel, imagine, and create
Contributes to a positive mood and emotional control Affects our mood and emotions
Keeps the body healthy Increases the risk of obesity

Who is Matthew Walker?

Matthew Walker

Matthew Walker was born in 1972 in Liverpool, UK, where he graduated in neuroscience from the University of Nottingham in 1996. He also received his PhD in Neurophysiology from Newcastle University in 1999. Matthew Walker is a professor of neuroscience and psychology and taught psychiatry at Harvard University for about three years. Matthew is the founder and director of the Sleep and Neuroimaging Laboratory at the University of California, Berkeley, where he has taught neuroscience and psychology since 2007. He is the author of numerous scientific studies published in leading journals. He spent four years writing his first, best-selling book “Why We Sleep” published in October 2017, in which he contends that sleep is the pillar of good health, and depriving ourselves of it may be the cause of many deadly diseases, including dementia.

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