for part one of this review, see http://www.josephazize.com/2021/05/03/review-walker-why-we-sleep/
Part Two: Why Should You Sleep?
I have always felt, and Walker establishes that: “Sleep is not the absence of wakefulness. It is far more than that. … Numerous functions of the brain are restored by, sleep. No one type of sleep accomplishes all. Each stage of sleep – light NREM sleep, deep NREM sleep, and REM sleep – offer different brain benefits at different times of night. Losing out on any one of these types of sleep will cause brain impairment” (108). That is documented in the balance of the book, but the most dramatic evidence relates to memory and learning (I shall not attempt to summarise it). Also intriguing is that being rocked to sleep provides objectively better sleep (118)
It is sober news for those who often wake before they have had eight hours sleep, that the most important sleep for motor-skill enhancement, is the sleep we usually have during the last two hours of it (127). Personally, it seems to me that the first period of sleep, let us say six hours, prepares us for the last hour or so. That may be why it has long been noted that the most significant dreams often come just before we awake. But now there is another, most important aspect of all this, and that is how we can habituate ourselves to poor sleep, and not realise that that is what we have done:
With chronic sleep restriction over months or years, an individual will actually acclimate to their impaired performance, lower alertness, and reduced energy levels. That low-level exhaustion becomes their accepted norm, or baseline. Individuals fail to recognise how their perennial state of sleep deficiency has come to compromise their mental aptitude and physical vitality, including the slow accumulation of ill health. (137)
Sleep loss and alcohol then have not an additive but a multiplying effect, so that together they make the consequences of the other much worse. (140) Sleep loss also increases the level of what Walker calls “circulating endocannabinoids,” which like cannabis, stimulate the appetite, and can tip people into gluttonous behaviour. (174) For this and other reasons: “inadequate sleep is the perfect recipe for obesity …” (175) Related to this, a full night’s sleep helps the communication pathway between certain parts of the brain: namely, those where there are pleasure-seeking desires and the “higher-order brain regions whose job it is to rein in these cravings” (176) with the result that one can more wisely direct one’s eating (176). It seems to me that this implies that good sleep helps the connection between the intellectual and emotional and instinctive functions. Sleep helps us respond to vaccines (183). Incidentally, if you are teaching, see pp.155-156 for important material about exams and the better organisation of testing knowledge in classrooms.
Soberly, sleep deprivation in childhood is a fairly sound indicator of later drug and alcohol use, and is associated with psychiatric illness – but what Walker argues is that poor sleep may be a factor in developing these illnesses (149-150). He emphasizes that this does not mean that all such problems are caused by a lack of sleep, but that sleep is a much neglected in causation and maintenance, so that improving sleep by cognitive behavioural therapy for insomnia (see the twelve tips) can alleviate psychiatric problems (151).
Walker ends this part of the book by saying:
The less sleep an individual obtains, or the worse the quality of sleep the more damaged the capstone telomeres of that individual’s chromosomes. … Neglect sleep, and your deciding to perform a genetic engineering manipulation on yourself each night, tampering with the nucleic alphabet that spells out your daily health story. Permit the same in your children and teenagers, and you are imposing a similar genetic engineering experiment on them as well. (188-189)
