Why We Sleep
Overview
I picked up this book as I’ve happened to hear about it from several people. It aims to be a fairly comprehensive primer on all sorts of sleep-related concepts—what sleep is, the different parts of sleep, things that sleep affects, and things that affect sleep.
My main takeaway: sleep is important, and we’re probably both (a) not getting enough sleep and (b) not recognizing that. While there’s plenty of other information, I’ve mainly been prompted to try to be a bit better around my own sleep routines.
I suspect that you can get many of Walker’s main points by just searching around. For that reason, I actually wouldn’t recommend getting the book—unless you are curious about diving deeper into one of the topics it covers.
My interest was pretty variable—I was interested in the mechanics of sleep, reasons behind it, and factors affecting sleep. The rest I ended up skimming or skipping. Likewise, you’ll probably want to jump around these notes.
Why We Sleep has also received some criticism, which I’ll touch on as well.
Importance of Sleep
The main takeaway of this book: sleep is really, really important.
Walker starts the book with shock/scare tactics, trying to warn you about all the negative effects that occur to people who don’t get enough sleep. There’s reduced performance (as you probably already know), but apparently lack of sleep can lead to sickness, psychiatric condititons, and other risks.
So, basically, get good sleep.
Walker says people should be regularly getting 7-9 hours of sleep, and seems to often push for 8. He claims getting less sleep than this is what will lead to degraded performance and/or illness. The criticism mentioned above questions these exact numbers.
I’m interpreting this pretty simply—set up healthy sleep habits, then let your body do its thing. Over the past few weeks, I seem to average slightly less than 7 hours per night.
Sleep Mechanics
Sleep Factors
There are two factors that drive our need for sleep.
The first is our circadian rhythm, which I’m assuming you’re loosely familiar with. It’s essentially an internal clock on a roughly 24 hour cycle. Typically, our brains use daylight to align this clock.
This cycle affects lots of our bodily functions, including when we feel tired. It’s “shifted” a different amount per person (imagine a sine curve shifted forward/backward). This is why some people are early risers while others are night owls.
The second is sleep pressure. Adenosine builds up in your brain as long as you’re awake. Once enough adenosine has built up, you’ll feel the need to sleep. Adenosine levels then drop while you’re asleep.
These two factors aren’t tightly coupled. That’s why you’ll sometimes feel quite awake even though you pulled an all-nighter—sleep pressure makes you tired, but your circadian rhythm acts as if you should be awake.
Sleep Cycle
By tracking brain waves, eye movement, and muscle activity, scientists have been able to classify some distinct phases of sleep.
Overall, there are two main phases: NREM and REM sleep. The names refer to how your eyes move during that phase of sleep: NREM = non-rapid eye movement, REM = rapid eye movement.
We alternate between the two phases as we sleep. A cycle takes roughly 90 minutes to complete. It starts with NREM sleep and ends with REM sleep. The ratio of NREM to REM sleep actually varies per cycle—earlier cycles are dominated by NREM, and later cycles have increasingly greater proportions of REM sleep.
NREM Sleep
Our brain waves have a unique characteristic during NREM sleep—they fire at a relatively slower rate, and are synchronized. While awake, activity is more chaotic/random and more frequent.
A main purpose of NREM sleep seems to be persisting long-term memories. This serves two functions—not only does it persist the memories, it also frees up space for more short-term memories. It sounds analogous to RAM and actual disk storage.
REM Sleep
REM brain waves look similar to brain waves when awake. From Walker’s description, it sounded to me as if the brain is testing its wiring—firing various connections and seeing what happens.
During REM sleep, the brain disables motor control. This prevents these firing neurons from actually causing you to do things.
When firing during REM sleep, it seems that the brain somehow encourages more “novel” connections—it somehow supports more disjoint neurons (?) to connect. This presumably is what allows us to come up with unexpected associations, solve problems, develop understanding, and to be creative while asleep.
REM sleep is also where dreaming occurs. It seems that dreaming also plays a critical part of sleep—it allows us to process emotional experiences. Our brains relive experiences while disabling emotional responses, allowing us to go through an experience without getting overwhelmed.
Dreaming can apparently also increase our performance on a task or skill, provided our dreams are actually related to that topic.
Influences on Sleep
A significant factor in our sleep cycles is modern society. A significant part of this comes from the schedules that the world runs on, which in turn affect when we need to be awake.
Other significant factors include caffeine, alcohol, and light.
Caffeine lasts a while, so late caffeine consumption can keep you awake longer than when your body would otherwise sleep. Caffeine works by competing against adenosine (the chemical responsible for sleep pressure). By binding to adenosine receptors, it prevents your body from feeling that sleep pressure.
Alcohol also lasts a while, so drinking later in the day will impact sleep. Alcohol works by inhibiting the brain—while it can shut down the things that keep you awake, it can also shut down the processes needed for good sleep.
Artificial light messes with the body’s expectation of natural light.
Walker also notes that all current sleeping pills aren’t actually effective. They sedate people, but don’t actually do anything that triggers sleep.
To improve sleep, Walker has a several items for good sleep hygiene. I’m sure it’s published online in various places.
Criticism
Alexey Guzey’s article questions a lot of Walker’s book, doing so by pointing out false claims in Walker’s book. Its point is that misleading or wrong claims may lead someone to worsen their lives by trying to get what they believe to be better sleep.
Many of these criticisms I actually find irrelevant. Most of them don’t impact me personally, and some I find slightly pedantic. It might be a bit more relevant if you actually have a sleep-related condition or are undergoing a sleep-related treatment.
With that said, the underlying point is still there—if Walker is wrong on these things, he could be giving a lot of other misleading info.
Guzey’s biggest point is that sleeping less than 7 hours a night is not necessarily harmful, and that someone could be wasting a significant portion of their life if they try to force 8 hours of sleep.
This is where I fall back to the greater point and personal experience: I should aim to give myself conditions for good sleep, then sleep for however much my body says it needs.