Book review of Alice Gregory

Alice Gregory:
"Nodding Off" (Bloomsbury, 2018)
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Alice Gregory does a good job of discussing current theories of sleep, but maybe it shouldn't be called "the science of sleep" (the book's subtitle) as she gives us no certainties about the current theories. If all scientific theories are only approximations, the theories about sleep sound like pure guesses, and based on precious little knowledge about the functioning of the brain. There isn't even consensus on why we fall asleep at some point of the day, nor why we have to sleep at all, nor what happens to our brain when we are asleep. Of course we know about the circadian clock, but it is obvious that the circadian clock is not the whole story because, unlike the heartbeat or breathing, it issues "suggestions" rather than "orders": we get tired and it's up to us if and when we want to actually fall asleep. She briefly (too briefly) introduces the various kinds of brain waves. If we had a science of sleep, we would read about these brain waves in all the following chapters, whereas they tend to become a mere footnote. The brain regions involved in the switch between wakefulness and sleep are vague (for example, an area of the hypothalamus becomes more active, which tells us very little about the rest of the hypothalamus, let alone of the other parts of the brain). We assume that some neurotransmitters trigger one or the other state, but the list begins with "such as" instead of being a precise list of which neurotransmitters are involved, what each one does, and why there is more than one. Worse: there are many theories for why we sleep and why we dream, but not much consensus. For example, the theories that sleep gets rid of dangerous toxins is credible until you start wondering why those toxins cannot be eliminated during wakefulness. The most popular theory is that sleep is the time when the brain consolidates long-term memory. There is even a theory, due to Matthew Walker, that sleep is a form of psychological therapy. Gregory briefly surveys theories of dreaming (notably Hobson's) but clearly this is not the core of the book. Each chapter of the book is about a specific age group, starting with toddlers and ending with "older adults". We learn that the circadian clock is not well developed in toddlers and that's why toddlers have trouble adapting to sunlight and darkness. She offers tentative explanations for sleep terror and sleepwalking among children, and for why teenagers want to sleep until noon and party all night. She suspects that there is something wrong in the timing of school and that it would help to shift school time by a few hours. She mentions studies according to which teenagers are more likely to get depressed an even suicidal if they stay up till late. Sleep-deprived brains are clearly a problem throughout the ages, which scary correlations with depression and suicide. Sleep deprivation seem to be correlated even with gaining weight. Gregory points out that we now restrict smoking to protect people's health but we do nothing to protect people's sleep (eg to avoid long hours of work) despite knowing that sleep deprivation can be even more harmful than tobacco. She mentions studies that show how people who have difficulties falling asleep or wake up at night are more likely to die younger. She talks of a "sleep-deprivation epidemic" in modern society.

We learn that psychopaths generally sleep well: they are not anxious at all. Clearly information about sleeping habits can provide clues to what will happen later in life. We learn how important sleep is for learning and unlearning. There's an interesting (tentative) genetic theory of amnesia. We are told to eat well and exercise, and be careful with medications, including sleeping pills.

This is all fine, but the limitation of the "science" of sleep is that it still falls (largely) into the anecdoctal category. For example, there is little here to show what sleep deprivation does to the brain circuits and the cognitive functions that control the motivation to live (or die), what physical processes lead from A to B, and, ideally, not just a qualitative but also a quantitative discussion. Otherwise it's impossible to make predictions. We can only say that "generally speaking" or "for most people" or "sometimes" something happens, and even that "something" can be very vague (some people call "depression" what other people call "bad mood").

The book provides an excellent panoramic on the current state of sleep science, but take everything with a grain of salt: without a quantitative description of brain processes, it is impossible to make predictions based on behavior.