Books for Dinner - 2021 - Chapter 03

Books for Dinner - Diverse food for a healthy mind!

[ 2021, Chapter 3 ]

"Why We Sleep"

By Matthew Walker

?You will definitely not fall asleep while reading this book - although the author states that he'd be delighted if you do since sleep has countless benefits. This book is full of amazing facts about sleep, proved by research. I will focus only on three in today's article, but feel free to explore the book for many more.

?#1. What's your rhythm?

Remember walking up at 7 a.m. although you wanted to sleep late that day? You can blame your suprachiasmatic nucleus for that. If you're at the opposite site and you usually get up late, well, the culprit is the same.

This part of the brain, called the suprachiasmatic nucleus, is "your twenty-four-hour biological clock". It signals out whether it is day or night using melatonin as a messenger. It gives us our own twenty-four hour rhythm called the circadian rhythm. But this rhythm might be different between you and me.

There are three chronotypes:

1.1. "morning types" - colloquially known as "morning larks". They go to sleep early in the evening and wake up early in the morning. Approximately 40% of the population has this chronotype.

1.2. "evening types" - colloquially known as "night owls". They usually fall asleep late at night and wake up late in the morning or in the early afternoon. Approximately 30% of us are in this category.

1.3.The remaining of 30% are between the two categories.

Your chronotype is given by genetics. Knowing yours is helpful to understand yourself better. For example, if you're a "night owl" and you wake up very early, you might not function optimal for a couple hours in the early morning. Your prefrontal cortex needs a little time to warm up. That is how it is wired, have patience with yourself. If you're a "morning lark", you'll experience full wakefulness in the morning, close to the afternoon. That might make it difficult for you to work late in the evening.

?#2. Remember yesterday's learning?

The hippocampus is the region of the brain storing short-time memory. But it has a limited storage capacity. During sleep, memory consolidation happens. Memories, information, facts are transitioned from the hippocampus (short-term) to the cortex (long-term).

This is very important for learning. Studies have shown that those who sleep after learning (day nap or the night after) have a remarkably learning advantage compared to those who don't. If we would have known this during faculty, would we still have spent those nights of late learning before an exam? Probably not. If you miss one night of sleep, that memory consolidation will not happen. And this is not something you can recover with more sleep in the following days.

I was particularly impressed by an experiment aiming to inquire whether the brain continues to learn without further practice and, if yes, whether sleep has a contribution to this. It's also interesting how Matthew Walker got the idea for this experiment. A pianist approached him after a lecture and expressed his surprise for a recurring situation: he was practicing a piece, but not yet mastering it, and the next day, after sleep, he was able to play it perfectly. What Matthew Walker discovered is amazing: yes, the brain "will continue to improve skill memories in the absence of further practice" (page 125) and this happens exclusively during sleep, not while being awake.

?#3. Have you slept?

Sleep deprivation is extremely dangerous for many reasons detailed throughout the book. Just a few below:

3.1. A study done in Australia showed that people who were sleep deprived for one night had the same cognitive capacity as those who were drunk with 0.08% blood alcohol. What's making this even worse is our inability to correctly evaluate our cognitive capacity in those moments, we're overestimating it. Combining the two: alcohol and sleep deprivation leads to multiplication of their effects, not to addition.

3.2. We are more irrational when we're sleep deprived. To understand why, scientists looked at the amygdala, part of our limbic system and responsible of triggering the fight-or-flight-or-freeze response. For sleep-deprived persons, the amygdala was 60% more active. Thus, the limbic system takes over and the prefrontal cortex doesn't get a say in how we react.

3.3. Hunger is higher when we're sleep deprived. Leptin is a hormone that signals satiety. Ghrelin is a hormone that signals hunger. What lack of sleep does is amplifying ghrelin ("I'm hungry") and decreasing leptin ("I'm full"). What's even worse than having our impulse control decreased by this combination and eating more, is that we'll be more attracted towards high-calorie foods.

3.4. Sleep deprivation weakens the immune system.

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Now that you know all that, what can you do to improve your sleep? The author references "The Twelve Tips for Healthy Sleep" in the book and actually has an appendix with them. They are no longer available at the link from the book, but you can find them (with some updates) here: https://www.nhlbi.nih.gov/files/docs/public/sleep/healthysleepfs.pdf (page4)

?I am definitely going to read this book again.

Note:?This article contains my view on this book and can be considered a review. The intention is to spread knowledge. The copyright for the original ideas belongs to the specified authors. The quotes are taken out of the book .