As humans, why must we sleep roughly a third of our lives? What is the function of our dreams? If these questions intrigue you, consider reading Matthew Walker's excellent book Why We Sleep. The book delves into all aspects of sleep from a person who is passionate about the subject. It starts by discussing the different portions of our sleep, including REM sleep, when our eyelids flicker while the rest of our body is paralyzed, and the very deep NREM sleep with its associated rhythmic brain waves. The book talks about what controls the circadian rhythms in our sleep, from the suprachiasmatic nucleus, which samples the light near our eyes, to the different chemicals, melatonin and adenosine, that are part of these daily sleep rhythms.
Interestingly, much of what we know about sleep was discovered by explorers, who subjected themselves to the tremendous darkness deep in Mammoth Cave and performed sleep experiments. The book goes into great detail about exactly what happens when we go into deep NREM and REM sleep. In particular, memories are initially formed in the hippocampus, which acts as a short-term repository; in REM sleep, many connections are made, and the memories are spread throughout the cortex, which can be seen in fMRI imaging. The book presents a nice analogy of how our mental picture is like a sculpture, and NREM sleep takes off bits of it, whereas REM sleep refines and solidifies the features. The balance between these two types of sleep changes throughout our life as we have different needs for creating connections and removing extraneous memories. Even the nightly balance between the two changes, with more REM sleep later on.
The book also discusses the bad things that can happen to us if we don't sleep enough, from obvious consequences of getting into car accidents or forgetting things, to diseases, such as cancer, heart disease, and obesity. The book finishes with a lengthy discussion of what we can do if we can't sleep and how medicines for insomnia work. It presents some simple rules for getting a good night's sleep, such as avoiding alcohol and caffeine and keeping a regular bedtime. One suggestion I found interesting was staying away from blue LED light at night. Although its discovery in the '90s resulted in a Nobel Prize, blue LED light has been bathing people in sunlight-like light more and more in the evenings from our many screens, impacting sleep.
Overall, I felt this was a great read from a person very committed to the subject.
Why We Sleep: Unlocking the Power of Sleep and Dreams
by Matthew Walker
