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Why We Sleep: Unlocking the Power of Sleep and Dreams

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Neuroscientist and sleep expert Matthew Walker provides a revolutionary exploration of sleep, examining how it affects every aspect of our physical and mental well-being. Charting the most cutting-edge scientific breakthroughs, and marshalling his decades of research and clinical practice, Walker explains how we can harness sleep to improve learning, mood and energy levels, regulate hormones, prevent cancer, Alzheimer's and diabetes, slow the effects of aging, and increase longevity. He also provides actionable steps towards getting a better night's sleep every night.

360 pages, Kindle Edition

First published September 28, 2017

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About the author

Matthew Walker

26 books1,889 followers
Matthew Walker is a British scientist and professor of neuroscience and psychology at the University of California, Berkeley. His research focuses on the impact of sleep on human health and disease. Previously, he was a professor of psychiatry at Harvard Medical School.

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Displaying 1 - 30 of 16,877 reviews
Profile Image for Bill Gates.
Author 10 books509k followers
December 12, 2019
Back in my early Microsoft days, I routinely pulled all-nighters when we had to deliver a piece of software. Once or twice, I stayed up two nights in a row. I knew I wasn’t as sharp when I was operating mostly on caffeine and adrenaline, but I was obsessed with my work, and I felt that sleeping a lot was lazy.

Now that I’ve read Matthew Walker’s Why We Sleep, I realize that my all-nighters, combined with almost never getting eight hours of sleep, took a big toll. The book was recommended to me by my daughter Jenn and John Doerr. Walker, the director of UC Berkeley’s Center for Human Sleep Science, explains how neglecting sleep undercuts your creativity, problem solving, decision-making, learning, memory, heart health, brain health, mental health, emotional well-being, immune system, and even your life span. “The decimation of sleep throughout industrialized nations is having a catastrophic impact,” Walker writes.

I don’t necessarily buy into all of Walker’s reporting, such as the strong link he claims between not getting enough sleep and developing Alzheimer’s. In an effort to wake us all up to the harm of sleeping too little, he sometimes reports as fact what science has not yet clearly demonstrated. But even if you apply a mild discount factor, Why We Sleep is an important and fascinating book.

Because this is a short review, I’ll answer a few questions that I suspect are top of mind for you.

Does everyone really need seven or eight hours of sleep a night? The answer is that you almost certainly do, even if you’ve convinced yourself otherwise. In the words of Dr. Thomas Roth, of the Henry Ford Hospital in Detroit, “The number of people who can survive on five hours of sleep or less without impairment, and rounded to a whole number, is zero.”

Why do we sleep? After all, when you’re sleeping—and all animals do—you can’t hunt, gather, eat, reproduce, or defend yourself. Yet Walker concludes that the evolutionary upsides of sleep are far greater than these downsides. In brief, sleep produces complex neurochemical baths that improve our brains in various ways. And it “restocks the armory of our immune system, helping fight malignancy, preventing infection, and warding off all manner of sickness.” In other words, sleep greatly enhances our evolutionary fitness—just in ways we can’t see.

What can I do to improve my sleep hygiene?

- Replace any LEDs bulbs in your bedroom, because they emit the most sleep-corroding blue light.

- If you’re fortunate enough to be able to control the temperature where you live, set your bedroom to drop to 65 degrees at the time you intend to go to sleep. “To successfully initiate sleep … your core temperature needs to decrease by 2 to 3 degrees Fahrenheit,” according to Walker.

- Limit alcohol, because alcohol is not a sleep aid, contrary to popular belief. While it might help induce sleep, “alcohol is one of the most powerful suppressors of REM [rapid-eye-movement] sleep,” Walker says.

- If you can possibly take a short midday nap like our ancestors used to and some Mediterranean and South American cultures still do, you should (but no later than 3 pm). It will likely improve your creativity and coronary health as well as extend your lifetime.

It took me a little longer than usual to finish Why We Sleep—ironically, because I kept following Walker’s advice to put down the book I was reading a bit earlier than I was used to, so I could get a better night’s sleep. But Walker taught me a lot about this basic activity that every person on Earth needs. I suspect his book will do the same for you.
Profile Image for Tharindu Dissanayake.
283 reviews505 followers
October 13, 2021
"The shorter your sleep, the shorter your life span"

This is not a book that I had in any of my reading lists, and only picked up because the title seemed interesting while I was searching for some other books. I'm really glad that I did so, because this turned out to be one of the most incredible books I've ever read: full of enlighteningly descriptive insights on many aspects related to sleeping.

"Wakefulness is low-level brain damage, while sleep is neurological sanitation."
"When sleep is abundant, minds flourish. When it is deficient, they don’t."

The books contains four main standalone parts, starting with explaining what sleep really is, then moving across how/ why should we sleep and dream, and finally on establishing proper sleeping habits. The reader will have the opportunity to learn about different stages of sleep and their functions with a staggering amount of examples and research references to better comprehend the principles outlined. And unlike most health related books, Walker's writing is excellent for readers of any prior background on the area. It made the reading experience very smooth and entertaining.

"REM sleep is what stands between rationality and insanity"
"The REM-sleep dreaming brain was utterly uninterested in bland, commonsense links – the one-step-to-the-next associations. Instead, the REM-sleep brain was shortcutting the obvious links and favoring very distantly related concepts. The logic guards had left the REM-sleep dreaming brain."

It is indeed alarming - as the author has stated throughout the book - how unaware we are about the importance of sleep to all beings. I, for one, had never even dreamed of such severe implications due to poor quality or reduced sleeping, but shared the common misconception of being wake up more is important for success in all areas in life. This book not only correct such mistaken beliefs but will cause a paradigm shift in how we should embrace proper sleeping habits, and soon.

"Humans, modern-living or pre-industrial, need less than seven hours of sleep therefore appears to be a wishful conceit, and a tabloid myth."

I cannot emphasize enough, how important it is for every single person to read this book, and cannot thank the author enough, for this is undoubtedly one the most helpful books one can ever read. I believe everyone should read this - irrespective of any and all variables - and the only worry you will have is not having read it sooner. Read this book, and as soon as you can!

"Memories formed without sleep are weaker memories, evaporating rapidly."
Profile Image for K.J. Charles.
Author 59 books8,142 followers
October 6, 2017
This book is genuinely terrifying. The author, a sleep scientist, lists the devastating consequences of getting less than 7-9 hours regularly and it is so much worse than you might have thought. SO much worse. We're basically all going to die.

I'm not even kidding--being just an hour short on sleep a day will do serious damage to your immune system almost immediately, and the Western world is in the grip of a massive sleep deprivation epidemic. Lack of sleep is a carcinogen, literally. It also destroys your ability to control your emotions and understand those of others, your memory, your creativity; it predisposes you to eat more *and* to put on more weight; oh, and it is closely linked to ADHD for the young and Alzheimers for the old.

Basically, if you go on Twitter and think "why is everyone and everything so absolutely awful" it's probably related to society-wide chronic sleep deprivation that people don't even realise they have. This book is genuinely horrifying (ironically, it will keep you up all night fretting). Some of the more striking findings are the absolute madness of night shifts and junior doctor rotas, the self destructive cruelty of school starts that require kids to be awake at 6, and the hecatombs of deaths caused by tired drivers. We've once again managed to set up a social structure apparently designed to cause as much mental and emotional harm as possible to humans. Well done us.

I would really like to dismiss all this as alarmist nonsense but the weight of research and the author's qualifications for writing this makes that quite hard, so instead I might just go to bed early forever. Really very scary and depressing to read, but seriously important. (Also highly readable and clearly written, unlike many books by experts for laypeople.)
Profile Image for Emily.
687 reviews623 followers
November 19, 2017
For once, I actually mean five stars in the sense of "everybody should read this book." This book is highly readable but contains stunning information I'd never seen anywhere else (and includes numerous references to serious primary literature).

I was reminded (stay with me here) of ancient Egyptian funerary practices. After carefully embalming organs like the heart and liver, and placing them in canopic jars, the Egyptians pulled the brain out with a hook and threw it away, because they didn't really know what it was for. This is how most modern people approach sleep. We know it must be sort of important, because why else would it be there, but we're quite foggy on the specifics and tend to give it short shrift. At worst, we see it as an "annoying and enfeebling" obstacle to other uses of our time.

Some standout topics here: your natural day/night pattern and the buildup of a chemical called adenosine in your brain that makes you sleepy, which contribute independently to your sleep cycle; and how caffeine and jetlag get you off your rhythm. (This was particularly interesting to me because I read this on a long flight. I never sleep on flights to Europe and this book explains why: I'm not sleep deprived enough to have excess adenosine to make me sleepy, plus it doesn't feel like nighttime yet when we depart. So my brain isn't interested in sleeping. When I arrive, my goal is to stay awake until 9pm and at first, it's easy. That's the "day" part of the circadian rhythm giving me a bit of a boost. But soon, that fades away and the extra adenosine comes crashing down.) The role of sleep in processing memories and new information: sorting out what's important, solidifying newly gained understanding, and turning traumatic experiences into bearable memories. How all creatures sleep, but in different ways that make the brain-repairing effects of sleep compatible with their environments. Some things that we think aid sleep, like alcohol and sleeping pills, are only useful if your goal is to lie inert in bed; they don't lead to true, restorative sleep.

Oh, and the doctor who developed the system for medical residents, and insisted that long shifts and little sleep were essential training, was a big-time cocaine addict.

There's some genuinely frightening information here as well. Sleep deficits cannot be made up (sleeping in on the weekends doesn't help) and lead to shorter lifespans. Lack of sleep contributes to Alzheimer's disease, mental illness, and cancer. (The WHO categorizes night shift work as a probable carcinogen.) Drowsy driving is more common than drunk driving and more dangerous. We may be seriously harming the country's teens by forcing them to wake up and go to high school at an hour so inimical to the circadian rhythm of that age group.

I already follow the author's advice about "sleep hygiene" so I was mostly attuned to the scientific information and arguments here about social ills. Many people in my sleep-deprived cohort may be genuinely alarmed to read this book. But that doesn't mean you shouldn't! I read so many nonfiction books with titles like this one that are ho-hum--but this one's a humdinger.

Review copy received from Edelweiss.
Profile Image for Emily (Books with Emily Fox).
531 reviews58.6k followers
Currently reading
August 11, 2021
I'm only 50% into and while it's good, if you have anxiety or if you're not sleeping well... don't read it!

I didn't need to stress myself more about sleeping badly. Now I know exactly how bad for me it is XD

PS. Guys, this isn't my official review, this is just me joking around that it's stressing me out lol
Profile Image for Mario the lone bookwolf.
797 reviews3,631 followers
June 14, 2020
The best book about the importance of sleep and the dangers of a lack of it.

Often it´s our own fault, because we eat too much too late, consume media before going to bed, don´t exercise, float the mind with negative and repetitive thoughts that come back at night, sadly not as succubi and incubi, but more the nightmarish evil, not sexy, demon style thing. Even if full 8 hours are reached, the quality can be so low that healthier people with an optimistic mindset find more regeneration with lesser sleep than that.

The consequences of sleeping too less because of work, too many hobbies or mental problems are as devastating as overweight, smoking, drinking, and many other harmful activities one normally avoids, but doesn´t care when it´s about finishing just one more level, one more chapter, one more project for work, one more beer with friends, one more episode, one more cancer, heart attack, virus infection due to a weakened immune system...

The funny thing is, we mostly don´t to it because of existential necessity, but to consume any kind of medium, have a longer good time with friends and family and intuitively think that the time is better invested in those activities than in 1 or 2 more hours of unproductive, forever lost hours of sleep. Cutting down to under 7, 6, sometimes even less seems legit to get more out of life and we don´t realize that we don´t just pay the expensive long-term price of higher mortality and more sickness, but that the following day is not as productive as creativity, workflow, concentration, and perseverance drastically drop and so we are slower, worse in any aspect, and unmotivated. Even if one sleeps the full 8 hours, the consequences of once sleeping too less or even not can reduce the performance for days, just as alcohol does the days after the hangover. Look how sad you make that poor little brain buddy there behind your eyes, what were you thinking when you did that, that reading is more important or what?

But, of course, it´s also societies fault and by forcing kids and teens to wake up far too early to go to school and pressing the last out of every working person, the current conventions produce immense unnecessary harm that could easily be avoided by better, progressive models of society and, once again, shining Scandinavia enters the limelight with the mantra "Social benefits and social security in a fair and strong eco-social welfare state make happy people."

Any drug around and before sleeping *cough beer cough* is a bad idea, alcohol before sleeping helps to fall asleep, but kills REM- sleep and sleeping pills are strong drugs with severe side effects like for instance killing oneself when accidentally overdosing. If there is already trouble with insomnia, one adds more problems to it by using chemical methods instead of finding out what the real cause is, changing something and searching help. In extreme cases, good old pharma is the only option, but many may not even try alternatives.

A big, but unsolvable, problem is the positive effect of sleep deprivation on people with depression and similar mental diseases. I don´t know how the harm of both illnesses could be quantified and compared, but both options seem to be horrible. To be desperately unhappy with full sleep and floating the body with stress hormones while diving ever deeper into the vicious cycle or too sleep far too less and be happier and more motivated, but meanwhile damaging the whole body.

This lucid dreaming thing is so extremely individual that one person might be close to unable to ever produce something satisfying while the other can do it as if it was nothing. That´s just random luck or bad luck, some people can add years and more quality to their lives by being conscious and creating any, totally real dream and fantasy wonderland and understanding personal problems, traumas and even solving them, while others can´t crack the brains code how to unlock the treasure chest.

A wiki walk can be as refreshing to the mind as a walk through nature in this completely overrated real life outside books:
July 2, 2019
Something to ponder; every living thing on earth is subject to the circadian (24 hour) rhythm. It is understandable why animals and plants need to be awake in daylight hours. Less so for fish that for thousands of generations have lived in underground rivers and have over the millenia lost the ability to even sense light. Even less so for bacteria. But still, all of us have this endogenous clock keeping time within us, keeping time with the sun.

In the 1930s, a scientist, Nathaniel Kleitman and a colleague attempted to change their body clocks. They spent a month in a cave, 140 feet underground with no natural light and a constant temperature of 54 °F. They used lanterns to regulate their "daylight". Each day they slept for 9 hours, worked for 10 and rested for another 9. They measured the rhythm of their body temperatures but could not adjust either that or themselves to the 28-hour cycle, it stubbornly remained at 24 hours no matter what.

One of the most intractible sleep disorders is that where the person's body clock does not conform to the universal circadian rhythm. The example given in the book is of a boy whose cycle shifts by an hour a day. For a few days a month he sleeps and is awake and working efficiently at the same time as his schoolmates. But nothing the doctor, the author could do, or any medication, could stop his natural wanting to sleep and wanting to wake to a 24 hour rhythm. The disorder made education very difficult, but as a man, he can work for himself and choose his own hours.
Profile Image for Trevor.
1,294 reviews21.7k followers
August 16, 2018
So, this book is both a must read and deeply, deeply disturbing. I’ve been having trouble sleeping for the last few years and now I’m going to have to do something about it, simple as that, because the consequences of not sleeping properly are appalling.

For instance, it provides you, free of charge, with an increased risk of diabetes, dementia (in all its fun and various guises), weight gain, heart disease and even accidental death. And the situation is getting worse. We are losing sleep at a rate of knots as we squeeze the nights from both ends. Add to that the fact that our world is now awash with night-time blue light – the frequency of light we have used to tell us it is day-time ever since before we were even fish – and this particular self-created train wreck just keeps a-roll’n along.

There were times in this where he would say things and I would think, ‘oh yeah, see that, you’ve gone too far this time’ – for instance, his saying that driving with a sleep deficit is worse than driving while drunk, having done both, I figured I knew better. But then he justifies this by saying that when you are drunk your reaction times are reduced, but you generally still react – but when you are sleep deprived you drop (without warning) into micro sleeps and while in them you do not react at all. You know, you are asleep.

And then he reminds us of the stereotypical truck driver (by the way, in most states in the US, there are more truck drivers than any other occupation). Truck drivers are often over-weight, which is directly correlated with sleep apnoea, that is, a condition likely to increase the number of times you fall into micro-sleeps. Did I mention I found this book terrifying?

The other bit of this that really struck me was the correlation between anxiety and a lack of sleep. It is almost as if we are unable to trust people as we get less and less sleep. And this also translates into an inability to lay down new memories – that is, learn things. In fact, something students often do is stay up all night studying for an exam – on the basis of ‘never do today what you can do five minutes before it is almost too late’. But such a lack of sleep is likely to leave them feeling under-confident, anxious and also seriously impaired in their ability to actually learn and remember anything they have spent the night staring blankly at.

This is part of the reason why he says the shift in the US towards earlier school starting times is such a bad idea. He presents an evolutionary biology just-so story that goes: adolescents need a safe-ish way to move out of the parental nest. They do this by their body clock shifting so they stay awake later (when their parents are asleep), so they can interact with other young people in a relatively safe environment, and this means they therefore wake later than their parents too. But then we force them out of bed at 6 or earlier to cross town to go to a school that starts at 7am, and getting up at that time feels to them like getting out of bed at 4am, bad things are likely to happen. How can they possibly learn in that state? Whether or not the evolutionary story is right, it does seem teens do need to stay up later and to sleep in longer, and we ought to respect that. It also seems there is such a thing as night-owls, and our forcing them to work at the crack of dawn is just as cruel and just as stupid as our forcing teenagers to do the same thing.

You need to get hold of this book and to read it – and it is written by someone who does research in the field, so, not just some random guy who likes nice good sleep-in in the morning and figures you should like it too. I can’t tell you how many times I thought while reading this, ‘oh, for god’s sake’. This was not the mirror I felt I needed to look into at the moment, but then, I guess that means it is exactly the mirror I needed to look into.
Profile Image for Greg Swierad.
44 reviews217 followers
July 28, 2020
Sleeping is probably the biggest productivity hack I know. If you don't get enough sleep every day or don't get regular sleep, this is the most important thing you should work on. Lots of bad decisions are made due to lack of sleep so no excuse just make sure you sleep well.
As important as sleeping is, writing a whole book about it feels like it's too much. I liked a lot of the things in this book but thought it was too long.
My biggest lesson from this book is to avoid sleeping pills whenever possible, and if there is a severe sleep problem you should see a sleep doctor for help.
You can read the full summary of this book together with the main action points in the BooksInAction app as well as here: https://www.mentorist.app/books/why-w...
Profile Image for ❀ Lily ❀.
77 reviews15.9k followers
January 24, 2021
4.5 - Very well researched and the studies/arguments are explained in a way that's very accessible and easy to understand.
Profile Image for Nicole.
446 reviews13.5k followers
May 15, 2023
Ciężko mi było przebrnąć przez początek, bo miał dużo informacji, o których wiedziałam. Później zrobiło się już typowo naukowo, czyli to co lubię najbardziej.
Niesamowicie ciekawa i otwierająca oczy.
Profile Image for Moeen Sahraei.
29 reviews27 followers
March 4, 2021
Five giant stars. This book is extremely precious because it is the intuitive summary of more than 50 years research on different facets and functions of sleep, and also because it is written by a proficient neurologist in a way that anyone can easily understand the intricate functions of the brain,hormones,body etc.
The author first thoroughly explains the endogenous reasons of sleep ( melatonin and adenosine ) and then describes two different phases of sleep ( NREM and REM ). Then he illustrates why we need sleep and how deadly and pernicious it is to avoid 8 hours sleep each night.
Several kind of cancer, Cardiovascular disease, diabetes, overweight, mental illnesses like depression and anxiety, memory loss, Alzheimer and so many disorders in learning process all ensue from sleep deficiency.
After reading this book you will definitely realize that sleep is such a blessing.
Profile Image for Mohamed Shady.
626 reviews6,648 followers
May 9, 2019
الموضوع طلع خطير يا جماعة، لو منمناش كويس هنموت، حرفيًا هنموت والله.
Profile Image for Warwick.
824 reviews14.5k followers
April 6, 2019
Matthew Walker really, really thinks we all need some serious shut-eye, and he's not messing around when it comes to getting you on board – he hits you with both barrels on page one, and never lets up:

Routinely sleeping less than six or seven hours a night demolishes your immune system, more than doubling your risk of cancer. Insufficient sleep is a key lifestyle factor determining whether or not you will develop Alzheimer's disease. Inadequate sleep—even moderate reductions for just one week—disrupts blood sugar levels so profoundly that you would be classified as pre-diabetic. Short sleeping increases the likelihood of your coronary arteries becoming blocked and brittle, setting you on a path to cardiovascular disease, stroke, and congestive heart failure […] sleep disruption further contributes to all major psychiatric conditions, including depression, anxiety, and suicidality.

And this is supposed to help me sleep better!? At least before, I just used to lie there going over the same three lines from ‘I Just Can't Wait to be King’; now, if I so much as drift into momentary consciousness at two a.m., I end up paralysed with alertness, calculating the gradually rising odds that my obese, cancer-ridden body will only cease to be a concern thanks to the merciful onset of my crippling dementia.

Eventually Walker just comes right out and admits that as far as the science is concerned, ‘wakefulness is low-level brain damage’, at which point you start to wonder how far he's really going to take this whole unconsciousness thing. But by then the damage is done. Your life is different. Come evening, when Hannah is pouring herself a glass of Sancerre and playing Gaga, I now appear in the doorway in my slippers, with a hot-water bottle clutched under one arm and a toothbrush jutting from my jaws. It may feel antisocial, but anything seems preferable to inviting the heart disease, obesity, cystitis, tennis elbow and plagues of locusts that Walker is otherwise promising.

A while back I got a Fitbit, which allows me to see in appalling detail just how much sleep I sometimes fail to get – the hypnograms, with their discrete stages of slumber, never quite stretching as far as you'd like them to. Thanks to this book, it's now possible to quantify exactly what I'm missing out on during such nights, as scientists have mapped more of the neurochemical processes involved than I ever realised: the deep, NREM sleep where memories are carefully transferred from short-term to long-term memory; then the ‘informational alchemy’ of REM-sleep dreaming, which sharpens creativity and conjures up solutions to our daytime problems.

The importance of sleep can be further appraised by its evolutionary heritage – it goes back about as far as life on earth. Walker finds that even ‘the very simplest form of unicellular organisms that survive for periods exceeding twenty-four hours, such as bacteria, have active and passive phases that correspond to the light-dark cycle of our planet’. Sleep is about the first thing natural selection locked in for us, and as far as we can tell every animal does it.

One always understood that sleep was a healthy thing, but somehow a full night of it is still often viewed as a luxury. On the evidence of this book, it's more like a medical necessity. Given working practices in many parts of the world, this is a big problem, and indeed part of Walker's mission is to explain that much of the developed world is suffering from a serious, chronic sleep deficit which is ultimately ‘a slow form of self-euthanasia’ – he is talking not just to individual sleepers, but to businesses and governments who have some responsibility to take what he says into account.

The difference between a four-star book and a five-star one is that while I might love both of them, I can keep a four-star book to myself, whereas a five-star book is one I can't shut up about to everyone around me. On that basis, despite its occasional infelicities, Why We Sleep makes the grade. It's passionate and clearly written, summarises a huge amount of research about which I knew little, and addresses a subject that obviously deserves the attention. It would take someone a lot more cynical than me to read this and not silently decide to make a few lifestyle changes – on which note, if you'll excuse me, I have some intensive, hi-octane pillow time to get to.
Profile Image for Clif Hostetler.
1,079 reviews712 followers
April 21, 2021
The less you sleep the shorter your life span will be. Do I have your attention yet? If so read this excerpt from the beginning of this book (p3-5), and you will understand why this book caught my attention.

This book is divided into four parts. Part 1 defines the nature and types of sleep, describes how the need for sleep changes over a life span, and goes on to discuss the evolutionary origins of sleep. Part 2 describes why you should sleep and lays out the dire consequences of not sleeping. Part 3 explains how and why we dream, and Part 4 takes on the broader societal issues in dealing with sleep needs. An Appendix is included for "Twelve Tips for Healthy Sleep."

The primary message of this book is to emphasize the importance of adequate sleep. There are some suggestions included for obtaining adequate sleep, but the primary message is why it's important for health. An indication of how important is that lab mice that are deprived of sleep die sooner than those deprived of food.

The book ties the lack of sleep to numerous illnesses, and then proceeds to make the case that lack of sleep is either the cause or part of a negative feedback loop making the illness worse. By describing physiological and neurological interactions the author is able to show how lack of sleep is involved in these processes. Then population and diseases statistics are referenced to verify the involvement sleep or lack of sleep.

For many readers of this book the author will come across as an alarmist because he takes issue with so many things that we assume to be part of normal life. He makes a case that the early hours for beginning school makes no sense for optimum student performance. He sites one study that showed the average IQ of students in a school district was increased by starting school later. The author also makes a case for ending the practice of giving medical interns long work hours.

Some readers will not appreciate the negative things that the author has to say about caffeine and alcohol. Incidentally, if you think alcohol helps you to sleep you need to see what this book has to say about that.

The following are four things I learned from this book that I decided are worth highlighting here:

1. Sleep is the process by which the body removes waste products of metabolism from the brain. (This includes amyloid proteins which are associated with Alzheimer disease.)

2. People who are sleep deprived show reduced sensitivity to insulin. (This is a precursor for diabetes.)

3. Sleep deprived people experience hormonal changes that increases hunger and decreases satiation. (This leads of obesity and the resulting consequences including diabetes and heart disease.)

4. Sleep plays an important role in changing new memories into long term memories. (Sleep is better than studying all night.)

The following are excerpts and quotations taken from the book with my introductory remarks:

Are you a night owl or morning lark? Here's a link to an excerpt (p20-25) on that subject.

Here's a link to an excerpt (p68-61) about Biphasic sleep.

Lack of sleep is such a common experience for many of us that at first it's hard to believe the case being made by this book:
"...linking it [lack of sleep] to numerous neurological and psychiatric conditions (e.g. Alzheimer's disease, anxiety, depression, bipolar disorder, suicide, stroke, and chronic pain), and on every physiological system of the body, further contributing to countless disorders and disease (e.g., cancer, diabetes, heart attacks, infertility, weight gain, obesity, and immune deficiency). No facet of the human body is spared the crippling, noxious harm of sleep loss." (p133)
The book makes a convincing case that:
"We are … socially, organizationally, economically, physically, behaviorally, nutritionally, linguistically, cognitively, and emotionally dependent upon sleep." (p133)
I've included the following quotation since it applies to many today who live busy lives, including me somtimes. Researchers have evaluated performance of sleep impaired individuals and have found some sobering facts:
Most worrying from a societal perspective, were the individuals in the group who obtained six hours of sleep a night, something that may sound similar to many of you. Ten days of six hours of sleep per night was all it took to become as impaired in performance as going without sleep for twenty-four hours straight. (p136)
Here's another quotation that caught my eye:
There is no major psychiatric condition in which sleep is normal. This is true of depression, anxiety, post-traumatic stress disorder (PTSD), schizophrenia, and bipolar disorder. (p149)
Regarding cardiovascular health:
Adults forty-five years or older who sleep fewer than six hours a night are 200% more likely to have a heart attack or stroke during their lifetime, as compared with those sleeping seven to eight hours a night.(p165)
Concerned about cancer?
…the scientific evidence linking sleep disruption and cancer is so damning that the World Health Organization has officially designated nighttime shift work as a "probable carcinogen."(p186)

Lack of sleep can leave you more prone to Alzheimers disease. World Economic Forum, Jan.3, 2018

Sleeping Too Little in Middle Age May Increase Dementia Risk, Study Finds New York Times, April 20, 2021

The Mysterious Link Between COVID-19 and Sleep The Atlantic, December 21, 2020
Profile Image for Andy.
1,377 reviews467 followers
January 2, 2021
This is artful science-writing, except that the science seems sketchy. It is fishy, especially in the context of the author's lambasting of Big Pharma, that he is a self-styled entrepreneur (https://www.sleepdiplomat.com/entrepr...) working with Fitbit and Google, presumably on the types of gadgets he recommends in the book.

Nerd addendum:
The general point is reasonable: people should get enough sleep. Fine -- that hardly requires a book. The potential plus-value here is the fear-mongering to motivate people to get more sleep, but I found his scare-stories frustratingly kooky. For example, the idea that zillions of lives would be saved by flu vaccine if only people got enough sleep is an enormous stretch. It is dangerous in general to extrapolate from laboratory observations, evolutionary psychology theory or principles of physiology to clinical/health policy recommendations. Yet much of the book is gee-whiz reporting on animal studies and "neurobollocks" research (see: Brainwashed: The Seductive Appeal of Mindless Neuroscience.)
Also, the problems of people who suffer from true sleep disorders are different from the general public problem of poor sleep hygiene. For example, people with debilitating insomnia may benefit from cutting out all caffeine, but even if that were true the evidence presented in the book doesn't justify telling everyone to do that.
Although I don't agree with all its points, the following article catalogs important problems in the book: https://guzey.com/books/why-we-sleep/. Other low-score Goodreads reviews list other non-facts. Some might find Guzey's tone off-putting but I try to focus on evidence and I appreciate that he makes verifiable statements of fact. One of Guzey's main falsifiable claims is that there's a U-shaped curve of mortality vs. sleep duration. He gives references to the peer-reviewed scientific literature. I checked one from the journal Sleep (https://www.ncbi.nlm.nih.gov/pmc/arti...) and it does say what he says it says: "In the pooled analysis, short duration of sleep was associated with a greater risk of death (RR: 1.12; 95% CI 1.06 to 1.18; P < 0. 01) ... . Long duration of sleep was also associated with a greater risk of death (1.30; [1.22 to 1.38]; P < 0.0001) ... . Conclusion: Both short and long duration of sleep are significant predictors of death in prospective population studies." This one fact by itself is a huge problem for Walker's book.
I think that in science, substance needs to matter more than surface.

Update Jan. 2021:
Please see comment stream below for interesting discussion.
Profile Image for Kamil.
213 reviews1,130 followers
May 26, 2018
There's an overwhelmingly positive experience I had with this book. For most of it, Walker talks about his research (and his colleagues) surrounding the sleep and those arguments are fascinating and convincing.
However, there are moments, mostly closer to the end of it, when you feel like you are listening to a sales pitch. First of all, I dislike when somebody uses percentage without reference, ie "it's a 150% growth" as it might easily mean it was 1% in the past and now is 2,5% (150% growth), which in some situation might be significant in others not at all. Second, the seek for real-life examples of dangers of the lack of sleep was on the border of simplification, as even though I didn't research it I'm pretty sure (due to the simple application of logic) that most outcomes are caused by a conglomerate of factors. When he talked about a drop in teenage accidents when school hours were moved one hour later, I couldn't stop thinking, that maybe it's not all necessary due to the fact that they drive better being well rested. For sure that's a factor but maybe if school started at 9, the hour most of the office jobs start, maybe some parents would drive the kids to school. This is just an example but that was bugging me.
When he mentions in passing Chernobyl disaster and blames it on lack of sleep, I was thinking it's such a shame that he sells himself so short, as this book is a great scientific study of sleep while this argument is just bananas. Sure tiredness played some role but the disaster was mostly caused by inherent design flaws and violation of safety measures.
All in all, a good read, just bear in mind he probably has a good intention in mind but is sometimes a bit blinded by his agenda.
Profile Image for Bharath.
596 reviews449 followers
April 1, 2021
Sleep has been a big mystery for long, as it has been unclear what purpose it serves, and why natural selection did not weed it out. After all, in earlier times, the period of sleep must have been one of considerable danger for humans (and even now for many animals and birds). And yet, sleep is a common requirement across the animal kingdom as well. In fact, birds and some sea creatures have the remarkable ability to sleep half a brain at a time.

Matthew Walker is a sleep scientist and does an exceptional job in this book of explaining what sleep achieves for us. In fact, sleep deprivation is extremely dangerous and there is not enough awareness of this. Modern lifestyle has dealt a blow to both our duration and quality of sleep, and the effects are already quite apparent.

While sleep has not completely revealed all its mysteries to us, a lot is now known after painstaking research over several years. Our sleep shuffles between NREM, Light and REM sleep – and all of them have their purpose. NREM sleep fortifies our memory helping in longer term recall, while REM sleep & dreams lend emotional balance and help us get to the big picture. The book discusses a large number of experiments detailing what happens when we skip sleep. Depending on the sleep cycle and the quantum of deprivation, the ill effects are nothing short of disastrous – lower immunity, failing memory, loss of emotional balance, pre-disposition to serious diseases such as diabetes, dementia and even cancer. Getting adequate sleep (~8 hours) on the other hand makes people more creative & productive other than being healthy.

Somehow, our cultures today do not emphasise the importance of sleep, as much as we do exercise and diet. So much so, that sleeping less is mistakenly regarded as a confirmation of working hard and being more ambitious. The assumption that each of us can do with varying periods of sleep is largely a myth as well. While a genetic mutation allows a few to function effectively with around 6 hours of sleep, this is extremely rare. Almost all of us do need ~8 hours of sleep. There are tips on improving sleep quantity as well as quality all through the book, such as regulating caffeine in the later part of the day.

Most of us are guilty of not according sleep the importance it deserves, and this book is an eye opener. This is a book everyone should read. There are very important points of note for individuals, educational institutions, hospitals, organisations and even governments.
Profile Image for David Rubenstein.
804 reviews2,538 followers
October 8, 2018
This is such an excellent book, mainly because I had never thought very much about the need for a good night's rest. The first part of this book does not really address "why we sleep". Instead, the book describes "what happens if we do not get enough sleep." Not until about halfway through the book, does the question "why we sleep" really get answered.

The author, Matthew Walker, is a professor of neuroscience and psychology. I always prefer to read science-related books that are written by scientists who are actively doing research in the field. They are the most authoritative, and they best understand all of the nuances involved in the interpretation of experimental results. As long as the science book is well written--and this book is definitely written in an engaging style--I always prefer to read a book written by an active researcher.

The author divides a night's sleep into two primary portions; the early portion is characterized mostly by NREM (non-REM) sleep, while the later portion is mostly REM sleep (Rapid Eye Movements). Both portions are essential. NREM sleep helps one to cement memories into permanent storage, while REM sleep helps one to apply past experiences to solve problems. If you skimp on either portion, then your brain has a very difficult time recuperating. The book describes, in just the right amount of detail, a host of experiments that have shown the deleterious consequences of insufficient sleep. And, I was really surprised by the range of consequences, and their seriousness. This book has thoroughly convinced me to make every effort to get a full night's sleep; at least 7 hours, and preferably 8 hours.

I am not going to try to recap the myriad consequences of insufficient sleep. Suffice it to say, they are truly scary. This is a fascinating book, and I highly recommend it to everyone who sleeps.

I didn't read this book; I listened to the audiobook version, as narrated by Steve West. He does a very good job keeping my interest throughout his narration.
Profile Image for Mark  Porton.
385 reviews326 followers
May 29, 2020
Why we Sleep by Sleep Scientist, Matthew Walker was totally BRILLIANT!

Matthew Walker is a British Sleep Scientist and Professor of Neuroscience and Psychology at Berkeley – and it shows. Essentially everything Professor Walker asserts is backed up by evidence. More often than not, he not only states the source but will explain the details of the studies in question to explain his statements. It is just so well done – all easy to read, all so well explained.

But this is all very well. It wouldn’t matter a Tinker’s Cuss if the message wasn’t so compelling.

We need 8 hours of sleep per night.

His introduction of why we sleep and how others in the animal kingdom sleep is fascinating. Facts like, some animals can sleep with only half their brains – WHAT?? – yes, half their brains, so the other half can keep the ‘body’ functioning. So, some aquatic mammals sleep with one half while the other is alert and keeping the animal swimming, otherwise they’d sink I suppose. The most interesting fact in this part for me was the line of birds whereby the bird on the left edge would have its left eye open and that half of its brain awake and open for business. All the other birds in line would be fast asleep, and the bird on the other end of the line to the right would have its right eye open and alert and half of its brain awake. How amazing is that? We humans think we’re clever!

We need 8 hours of sleep per night.

One other repeated message in this book is, we spend the first half of our night in light nREM and deep nREM sleep and then the second half in REM sleep. (REM = Rapid Eye Movement, as many of us know). In nREM sleep our brainwaves are slow, steady and predictable and in REM sleep our brainwaves are all over the shop like when we are awake. This REM period is when we dream, in my case pretending I am playing football for England or starring in the latest Series of Fleabag as the dishy Priest or being chased by Magpies. Both nREM and REM periods serve essential functions, for example, REM sleep helps with setting our memories from the previous day, re-igniting synapse connections, amongst so many other things – without which we can become sick. Yep sick.

We need 8 hours of sleep per night.

Regarding the amount of sleep we must have; the author says ”….humans (and all other species) can never ‘sleep back’ the sleep we have previously lost” He later goes on to explain the sad consequences of this, especially if it’s chronic – and it is frightening and true.

We need 8 hours of sleep per night.
It was also interesting to learn that those countries who gave up their regular siestas (something I love to do on the weekend) went on to suffer a 37 percent increase risk of death from heart disease, relative to those who maintained afternoon naps.

We need 8 hours of sleep a night.

I really don’t want to keep sprouting facts and passages from this book, otherwise there’s no point in you reading it. But if you’re interesting in being convinced about the importance of getting a solid 8 hours sleep a night (have I mentioned that?), and the effects substances like alcohol (this is frightening), sleeping tablets, other substances and the results of sleep deprivation (it can be lethal) and the myriad of conditions that ensue from lack of sleep. I highly recommend this book.

We need 8 hours sleep a night.

I am fortunate enough to read papers, studies and various journals in my line of work, and am always on the look out for outlandish, evidence-absent conclusions. But this book has sold me, look. During the time I have read this – I have made a point of sleeping by 11pm (with a book of course) and waking at around 7am – and each day I have felt as BRIGHT AS A BUTTON!! Still feel buggered late afternoon thought – that’s because I’m not getting any younger.

I have become a born-again sleeper and will tell everyone I know – and I can tell it’s wearing thin. But it is SO important.

Love this book, massive fan of this guy.

5 Stars

Many, many thanks to Netgalley for providing me with a copy of this wonderful book in return for an honest and objective review.
Profile Image for Bradley.
Author 6 books3,976 followers
March 13, 2019
You know, I'm not usually one to tout NY Times bestsellers, but in this particular case, I want to mention that...

This kinda should be required reading for everyone.

Why? Because despite the rather innocuous title and no-nonsense factual information being presented, with no less than 750 scientific studies supporting the findings within, the author OUGHT to have been screaming that we're all freaking fools and morons.

Sure, I've heard of some of the studies, such as the ones related to the huge probability of obesity and depression and cancer rates for people who don't get 8 hours of sleep, but when we see all the other facts involved with it are all laid out, I frankly despair. Our societies are made up of complete idiots.

Most of the most powerful and necessary REM sleep happens in the last block of sleep, between 6-8 hours. Most of us are reducing our sleep to 6 or less. Learning and retention and memory decrease as if you're constantly drunk, and the long-term effects short circuit all rational behaviors. We eat more because we act high. We get into more car accidents. Test performance is abysmal, as is our moods, our ability to digest foods properly, and our ability to resist the flu drops from an 18% chance at 8 hours of sleep to a whopping 50% chance when you get less than 6 hours. These are studies, based on people who, in a controlled environment, are swabbed with the sick. Think about that. Add VERY significant numbers to cancer, suicide, and total life dissatisfaction, and the picture becomes very dire.

Oh, and sleeping pills short-circuit the REM cycle. As do drugs for ADHD.

This is the funniest and most horrible thing I picked up here: Teens all have a natural change in their circadian rhythm. They all become night owls. So WTF are we forcing them to get up earlier and earlier to go to school? They AREN'T getting enough sleep. So what happens? They go in, do abysmally in school, show all the same symptoms as ADHD, get diagnosed with ADHD, and then get drugs to help them concentrate while only making the fundamental problem of not getting enough REM sleep WORSE.

*slow clap*


And I'm talking about ALL of us. Long term sleep deprivation is the thing we do to TORTURE PEOPLE WE DON'T LIKE. And yet, there's this thing about rewarding long work cycles, turning people in unthinking zombies with decreasing work productivity JUST BECAUSE we're trying to squeeze out that last hour of work? It's KILLING US. Literally. Our minds aren't working well enough to even realize there's a problem.

Put a STOP to this! Seriously, folks! This is right up there with dancing around in a cloud of radium. Oh, look, it's so pretty!

This is science, folks. Not a fad. Don't be an idiot.
Profile Image for Hamad.
1,012 reviews1,330 followers
January 6, 2019
This review and other non-spoilery reviews can be found @The Book Prescription

“The best bridge between despair and hope is a good night’s sleep.”

🌟 I am still on a quest to discover more non-fiction books, that started last year and I am willing to continue this year. So when Tala (Who also happens to be a medical student in my class) recommended this, I knew that I had to read it!

🌟 I also had the same first question that most of us will think of: How a ~370 pages book is filled with things on sleep?! This book answered many questions that I had thought about in my long sleepless nights. It explains why do we need to sleep, the evolutionary role of sleep, why do we dream and what are the benefits of dreaming, Why do we as teenagers and new adults like to go to sleep late while adults go early, why do you feel tired after you pull an all-nighter but then gradually get energized! And one of my favorite things is explaining why we like to keep one foot out of the bed at night!!

🌟 What is cooler about this is that it does so in a simple language that everyone can understand. No need to be in the medical field to do so. If you are interested in sleep then you should read this!

🌟 One of my professors once told me that people like to view the world in what they are best at. So a doctor will see everything as physiology and pathology, an engineer will see things as equations, numbers and drawings, a chemist will announce the secret of life as Alchemy. So a sleep scientist will explain everything by -you guessed it- Sleep!
As much as I enjoyed the book, I thought it was trying too much sometimes! There was a graph depicting the relationship between Obesity and sleep and it shows that through the years we have been sleeping less and thus becoming more obese. Which has a certain truth to it but we can not ignore the changes in food and lifestyles too!

🌟 Also the author would tell you that if you don’t sleep well (I assure you that 99% of us don’t) then you will get Alzheimer, cancers, obesity, diabetes and all sort of things… If you find this idea uncomfortable then you may want to skip this.

🌟 Summary & Prescription: I really enjoyed this book as much as I expected to. It is kind of scientific but still awesome to read. I like that the author provided concrete evidence -Although I want to discuss some things further more- through the book and that it was not all theories. I recommend this for all of you looking for a non-fiction book and are interested in Sleep!

Happy reading and Sleep tight I guess?
Profile Image for Ana  Lelis.
459 reviews150 followers
March 26, 2023
I'm going to sleep right now.

Joking apart, this book is so necessary. Since I was 14 I've always slept really badly, late and little.
I knew it was a bad habit, my friends and family were worried about the time I went to bed and the time I woke up. I knew it wasn't good, I had read about it. But, I've never taken it seriously. Now, that I'm getting older I'm feeling more tired and grumpy by my lack of sleep and decided to read this to help me change somehow.
This book covers the most critical aspects of sleep and, although I knew sleeping was important, I'm mesmerized by how crucial it actually is. From now on, I will try my best to sleep properly. I want to change, but also, people that I love and care about as well. If you are still reading this I highly recommend reading this book. If you are reading this at 2 AM go to bed RIGHT NOW. Thank me later.
Profile Image for Olive Fellows (abookolive).
586 reviews4,736 followers
June 3, 2021
Written by sleep scientist Matthew Walker, this is a look at what all we know about sleep right now. Though much about sleep is still not understood, Walker makes the bold assertion that more than anything else in our lifestyles, sleep is the factor that is the key to our overall wellbeing. Diet and exercise are important, but nothing is as crucial as getting the 7-9 hours you need every single night.

This is not a self-help book on how to sleep more, but understanding the science - presented in this book so expertly and so entertainingly - might be able to help you understand where (if anywhere) you're going wrong, and will make you treat getting those nightly Zzzs as a much higher priority than ever before.

Check out my full review on Booktube!
Profile Image for Amora.
189 reviews143 followers
April 3, 2020
After listening to Matthew Walker’s appearance on Joe Rogan’s podcast I decided to leave a review for this book. Overall, it’s quite good and the content is original. This book highlights the benefits of nine hours of sleep and how it is imperative to live a healthy life and do excellent academically. I didn’t think you could write so much over the research on sleeping. I do hope Walker appears on Joe Rogan’s podcast again to remind people to sleep more!
Profile Image for Alexey.
1 review9 followers
January 1, 2020
update: there's now an example of deliberate data manipulation by Walker (he edited out the data that contradicted his argument from the graph) -- https://guzey.com/books/why-we-sleep/...


Read my full review here: https://guzey.com/books/why-we-sleep/

Walker misrepresents science, invents things on the fly (e.g. sleeplessness epidemic declared by the WHO), and scaremongers everyone into sleeping more than they probably should. I wrote a fact-check of the first 10 pages of the book, and it's not pretty. The book is not far from pseudoscience.

Just in the first chapter (10 pages long) of Why We Sleep, Walker:

1. completely misrepresents the relationship between sleep and longevity and between sleep and cancer
2. erroneously states that getting a good night’s sleep is always beneficial
3. erroneously states that patients with fatal familial insomnia die because of lack of sleep
4.. seems to invent a “fact” that the WHO has declared a “sleep loss epidemic”
5. misrepresents National Sleep Foundation’s sleep recommendations and uses them to misrepresent the number of adults failing to get the recommended hours of sleep (Section 5)
5.1. also seems to invent the WHO’s sleep recommendations
6. calls his book “a scientifically accurate intervention”
Profile Image for Odai Al-Saeed.
875 reviews2,417 followers
May 5, 2019
لأولئك الأشخاص أمثالي الذين أرهقهم الأرق وازدادت مشاقهم في تحويل المسار الليلي للتفاهم مع عجلة النوم فانقلب الليل نهار والنهار ليل... تكمن أهمية الكتاب من حيث الدقة أن الكاتب أستاذ فلسفة سابق لعلم النفس في جامعة هارفرد كما أنه مدير مركز علوم النوم البشري في جامعة بيركلي المرموقة
هذا الكتاب بمثابة مضخة نفاثة لكم من المعلومات الثرية التي تتحدث عن أهمية هذا الجانب في حياتنا التي تؤكد أنها في المقام الأول من ناحية الأهمية متخطية غريزة المأكل والمشرب وإحتياج الجسم للحركة والرياضة....أعتقد أن كل سؤال قد تمت الإجابة عنه في هذا الكتاب وللناشر جزيل الشكر على هكذا إختيار وإنتقاء...لست بصدد الحديث التفصيلي نظراً لأن أهمية المعلومة على إختلافها سواء كانت علمية ،ثقافية ،سيكولوجية تختلف من قارئ لآخر كل ما أحببت أن أنوه به هو جودة محتوى الكتاب للحث على قراءته...الثلاث نجمات كون أن المواضيع كتراكمة قد يجد البعض فيها أجزاء تجلب على الملل وأتنمى لو أجد شخص يلخص هذا الكتاب بطريقة أكثر جاذبية نظراً لأهمية الموضوع
Profile Image for Ali Karimnejad.
313 reviews150 followers
April 28, 2022

بهترین کتاب نه، اصلا! اما مطمئنا مفیدترین کتابی که تا به امروز خوندم

سعی می‌کنم در این ریویو با کلیات اون چیزی که کتاب میخواد بهتون بگه آشناتون بکنم تا ببینید لازمه بخونیدش یا نه.

خور، خواب، شهوت!ا

همه ما آگاهی قابل قبولی راجع به بهداشت غذایی و بهداشت جنسی داریم ولی به ندرت کسی رو پیدا می‌کنیم که راجع به "بهداشت خواب" چیزی بدونه یا شنیده باشه. این در حالی هست که کمیت و کیفیت زندگی هر فردی بیش از اونچه که بتونه تصور بکنه به کیفیت خوابش گره خورده. طی آزمایش‌های متعددی که در این کتاب گردآوری و تشریح شده، کتاب توضیح می‌ده که چطور خواب بی‌کیفیت و ناکافی تا 400 درصد ریسک ایست قلبی رو افزایش می‌ده، عملکرد تجزیه شدن گلوکز در بدن رو مختل می‌کنه و منجر به دیابت می‌شه، چطور هرمون‌های اخطار دهنده "حس سیری" و "حس گرسنگی" رو مختل می‌کنه و منجر به افزایش وزن می‌شه، چطور گرایش شما به "جانک فود" رو افزایش می‌ده، و شاید بدتر از همه چطور پروسه‌های یادگیری مغز رو با اختلال مواجه می‌کنه بدون اینکه اصلا متوجه بشید یا چیزی حس کنید.

چرا می‌خوابیم؟!ا

بنظر میاد خیلی دیر متوجه این سوال شدیم. وقتی از منظر تکاملی نگاه کنیم، خواب یعنی "خود را در معرض خطر قرار دادن". یعنی "دریغ کردن فرصت جفت‌گیری و غذا خوردن". با این همه امروز متوجه شدیم، تمام موجودات زنده، حتی ساده‌ترین و بدوی‌ترین کرم‌ها و انگل‌ها هم به نوعی طی یک دوره ریتمیک، خواب رو تجربه می‌کنن. اما چرا؟! تشریح جواب به این سوال در این مجال مقدور نیست و هنوز هم جواب کامل و جامعی در مجامع علمی به این سوال داده نشده اما جواب خیلی کوتاهش اینه که بدون خواب ممکن نیست. خواب چنان با فعالیت تک‌تک اجزای سلول‌های زنده عجین شده که بدون خواب عملکردشون کاملا متاثر می‌شه.

پریود روزانه فارغ از هر جنسیت!ا

هر انسانی یک سیکل روزانه خودش رو داره. این سیکل دقیقا همون چیزی هستش که باعث می‌شه بعضی‌ها جغد باشن (یعنی کسایی که نزدیک صبح خوابشون می‌گیره). اما سیکل بدن شما فقط منوط به خواب شما نیست. طی یک سیکل کامل (به طور متوسط معادل با 24 ساعت و 15 دقیقه) دمای بدن، فشار خون و خیلی چیزهای دیگه در بدن شما در یک بازه محدود به طور منظم در نوسان هستن و روی سطح هشیاری، آمادگی جسمانی و خیلی چیزهای دیگه تاثیر مستقیم می‌ذارن. اخیرا همین یافته‌ها به شکل موثری در ورزش حرفه‌ای دارن بکار گرفته میشن و نتایج فوق‌العاده‌ای هم دادن.

سیکل بدن شما متاثر از عوامل خارجی نیست. و مشکل هم همینه. وقتی طی فصول مختلف، شب‌ها بلند و کوتاه می‌شه، یا مثلا وقتی به یک نقطه جغرافیایی دیگه مهاجرت می‌کنین، سیکل بدن شما تغییر نمی‌کنه و راه خودش رو می‌ره. این شما هستین که باید با سیکل بدنتون منطبق بشید. اونچه که به اون خواب موثر می‌گیم فقط در یک بازه بخصوص از این سیکل تعریف می‌شه و اگر میخواید موثر بخوابید، باید نه منطبق با تاریکی و روشنی هوا یا ساعات کار اداری، که بر مبنای سیکل بدنتون بخوابید.

نوار مغز طی خواب- جهش‌های متناوب بین دو حالت بسیار متفاوت

خواب ما انسان‌ها ترکیبی از دو نوع خواب مختلف به نام‌های رِم و اِن‌رِم هست که به شکل تناوبی، اما با سهم متغیر، تقریبا هر 90 دقیقه نوسان می‌کنن. اینکه چرا اینطوریه در این مجال نمی‌گنجه. اما بین این خواب‌های رِم و اِن‌رِم یک دنیا فرق وجود داره و هر کدوم از یک جهت ضروریه.
به طور خیلی خلاصه، خواب اِن‌رِم خواب بدوی‌تر هست که در بین همه موجودات زنده مشترکه. این خواب رو بهش خواب عمیق هم می‌گیم و خودش به چهار فاز تقسیم می‌شه از حیث میزان هشیاری. فقط طی این خواب هست که اطلاعات شما از حافظه کوتاه مدت مغز (هیپوکامپ) به حافظه بلند مدت (پری‌فرانتال‌کورتکس) جابه‌جا می‌شه و هر گونه کمبود یا اختلال در این فاز خواب، شدیدا بر قدرت یادگیری شما اثر می‌ذاره.

باز به طور خیلی خلاصه، خواب رِم، خواب رویابینی شما هست. امواج مغز شما طی این خواب، بسیار مشابه با نوار مغزی شما طی بیداری هست. تفاوت در اینجاست که طی این خواب غده تالاموس در مغز، که دریچه انتقال اطلاعات حسی به کورتکس هست، بر روی سنسور‌های دریافتی شما از قبیل چشم، گوش و زبان بسته می‌شه فلذا اطلاعات فقط از حافظه شما به کورتکس راه پیدا می‌کنه. اونچه که شما به عنوان رویا در خواب می‌بینید، چیزی جز ترکیبی بسیار مغشوش و پیچیده حافظه کوتاه‌مدت و بلند مدت شما نیست. و فراموش نکنید، بسیاری چیزها در حافظه شماست که شما در حالت بیداری به اونها دسترسی ندارید. اما همچنان در حافظه شما هست. این بحث در کتاب یکم با تئوری‌��ای خواب فروید مقایسه شده و خیلی جالبه. ولی مجال بیش از این نیست.

فقط به همین بسنده می‌کنیم که اگرچه خواب‌های شما اکثرا مغشوش هستن و حالا دلیلش رو می‌دونیم، اما انتظار می‌ره طبق روند تکاملی، خواب دیدن مزایایی داشته باشه و بعد از مطالعات بسیار طاقت فرسا، امروز متوجه شدیم که داره. خواب‌های معنی‌داری که شما می‌بینید یک پدیده بسیار پیچیده برای تخفیف دردها و دغدغه‌های روانی شماست. این رو با اندازه‌گیری فعالیت ناحیه ونترال‌تگمنتال در مغز، روی بیمارانی که دچار تروماهای شدید بودن متوجه شدیم. توضیحش طولانیه. اما مغز تلاش می‌کنه در فضایی که ترشحات هرمونی قطع شده اون خاطرات رو بازیابی کنه و به نوعی از اون خاطرات طلاق عاطفی بگیره. در همین حد قبول کنید!

‌البته خواب رِم فواید بسیار دیگه‌ای هم داره. در واقع ظهور تمام خصلت‌های پیشرفته انسان من جمله پیدایش زبان و درک ژست‌های بدن یا صورت که خصوصیات رفتاری بسیار پیچیده‌ای هستن همه شدیدا در ارتباط با خواب رِم و نوع فعالیت مغزی ما طی این خواب هست.

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