This book by Dr. Matthew Walker covers most aspects of sleep over four sections. The first, this thing called sleep, covers the details of what sleep is and the evolutionary origins of sleep and the different stages of sleep. It also details how different animals sleep and the amounts of time dedicated to each stage plus the cycles of sleep within different animals. Section two, why you should sleep, goes into additional details of why we sleep and the various benefits of sleep on our physical, mental, emotional and philological health. The third section is how and why we dream. The topic of this section is self explanatory. The final section, from sleeping pills to society transformed, discusses sleep and the issues surrounding sleep in modern Western society.
It turns out all animals sleep or rest in one form or another. It comes as non-trivial and not something you would think about. The extended lack of sleep for any animal can be fatal. This suggests that sleep is an essential part of the functioning of animals and should not be neglected. It also indicates sleep is one of the foundational elements of animals evolutionary history and sets us apart from other living beings on earth.
When it comes to mammals, those that live in the sea sleep with one half of their brain at a time. This allows them to stay conscious while resting so they can stay alert and keep swimming. They still rest for 8 hours a day though, 4 hours with one part of their brain and 4 hour with the other.
There are 4 different stages of sleep but they can be grouped into two general categories. One is non-REM sleep the other is REM sleep (very creative names, I know). There are many differences between NREM and REM sleep and each stage performs different functions. NREM sleep is when the brain waves move slower. It also brings the feeling of restfulness to you in the morning. REM sleep is the stage of sleep when you dream. It is also closer to wakefulness in terms of when it occurs. NREM and REM sleep are responsible for different nerve activities within the brain. Combined these stages are responsible mental health and memory function.
One interesting difference mentioned between NREM and REM sleep is the limbic system is disabled during REM sleep causing people not to act out their dreams. However, the limbic system is not disabled during NREM sleep. This means that sleepwalking occurs during NREM sleep. It is also the reason why sleepwalkers do not remember their activities during the time they are sleep walking.
Over the course of one’s lifetime the need for each stage of sleep and indeed the amount of time spent in each stage of sleep changes. Babies and small children get more deep NREM sleep and less REM sleep. This makes sense because younger children are growing physically much more during the early years of life. As people get older the balance of sleep cycles shifts towards more REM sleep.
Dr. Walker presents evidence of mental issues later in life due to lack of sleep. He makes the link to Alzheimer’s disease being caused in part by lack of sleep throughout life. One anecdotal example of this is Margaret Thatcher and Ronald Regan who both often bragged about only sleeping 4 hours a night. Ultimately they both suffered from Alzheimer’s which may have been avoided had they taken sleep more seriously.
Why We Sleep by Dr. Matthew Walker is fascinating and full of interesting information as to why sleep is important and should not be considered as part of a healthy lifestyle. I initially heard Dr. Walker and the discussion of these topics on The Joe Rogan Experience which you can find on YouTube, Spotify or most other podcast outlets. This book is also featured on Bill Gates’ blog Gates Notes.