It's almost a common knowledge that getting enough sleep is good for your health. But many modern people don't have access to quality sleep. Every year on World Sleep Day, we read all kinds of popular science articles, make up our minds to sleep well, and then continue to suffer from sleep for the rest of the day.
Why is it so hard to get a good night's sleep?Russell Foster, a professor of neuroscience at the University of Oxford, shares his research in "The Best Time", showing with compelling scientific facts the amazing impact that different times of the day can have on our health, proposing the idea of "good time" to follow the biological clock and get more health with less. Circadian clock science is not only about sleep, but also affects human cognition, memory, immunity, metabolism, mental illness, etc.
This article is excerpted from Chapter 9 of "The Best Time", published with the permission of the publisher.
Original author |Russell Foster.
The Best Time: How to Use Your Biological Clock to Live a Healthier Life, by Russell Foster, translated by Wang CenhuiStraits Book Company, November 2023.
The brain is as dense as cold cereal porridge, and we are not interested in this fact.
Alan Turing was an English logician and mathematician.
Albert Einstein was a textbook figure on the topic of genius and sleep. I often give him examples in lectures to illustrate that regular long sleep is intellectually beneficial. Einstein got 10 hours of sleep a night and then had a well-organized day, and as a result, he came up with the general theory of relativity and won the Nobel Prize in physics. Usually when I talk about this, someone raises their hand and asks, "What about the Spanish painter Salvador Daíl?"He doesn't sleep at all. You can't say he's not a genius, can you?My answer was, "Well said!".”
It is said that Dalí would sit in a chair with a key or spoon in one hand and a metal plate on the floor directly below. As soon as he fell asleep and let go of his hand, the key or spoon fell off and hit the plate, and he was woken up by the sound of the impact. Dali felt that sleeping was a waste of time. For him, and especially for his artistic creation, this may be the case, because constant sleep deprivation can induce paranoia, hallucinations, and impaired consciousness. During an attack, people can usually perceive vivid abstract pictures or sounds (which may also be smells or tastes).
Hallucinations plunge patients into a world of fantasy, with Dalí claiming that the melting clock in his famous painting "The Persistence of Memory" comes from hallucinations induced by lack of sleep. In contrast to Dalí, Einstein needed to use critical and discriminative thinking to understand the nature of the universe, and sleep helped him to understand reality clearly. Dalí wanted to have a surrealist view of the universe, and the distorted lens of sleep deprivation and impaired consciousness gave him a unique perspective.
Footage from the documentary "Scientific Sleep" (2006).
The definition of consciousness is quite broad and includes our awareness of our own unique thoughts, memories, feelings, sensations, and circumstances. Essentially, consciousness is our awareness of ourselves and the world around us. Einstein and Dalí are two extremes at the level of consciousness, and most of us are in the middle of the two. More precisely, our consciousness is greatly influenced by circadian time and sleep and circadian rhythm disturbances.
Cognitive abilities change throughout the day.
The word "cognitive" is used quite widely (e.g. in the phrase "your cognitive abilities"), but it is poorly understood. Let's start with the definition of the word. Of course, cognition contributes to our consciousness. Cognition refers to the many processes in which the brain operates, including collecting, understanding, storing, and responding appropriately.
In many cases, our actions draw on memories and past experiences. There are three key elements to cognition: one is attention, which is when we notice key features in our environment and filter out "irrelevant" information;The second is memory, which refers to our ability to store and retrieve information, short-term memory is formed first, and then "precipitated" into long-term memory;The third is executive function, which is related to the brain's ability to plan, monitor, and control complex behaviors that are designed to achieve a specific goal or complete a specific task.
In general, cognitive processes can be conscious, such as deliberately solving a problem;It can also be unconscious, such as when the brain focuses on environmental features or uses memories to solve problems without us realizing it, until a solution pops up in the form of a "flash of inspiration" or "insight."
The first thing to note is that our overall cognitive abilities (which can be assessed with a whole host of different tests) vary significantly over a 24-hour day. This day-to-day variation depends on the interplay between factors such as the circadian system, sleep patterns, sleep needs, and age. It's often difficult to tell what each of these factors played, but the end result is unequivocal: most adults wake up with a rapid increase in cognitive performance, peaking around noon.
A well-known study conducted by Australian researcher Drew Dawson showed that between 4 and 6 a.m., our cognitive abilities are worse than when we develop cognitive impairment after being drunk. This time effect makes it extremely dangerous for people to do any activity (especially driving) in the early morning – knowing that drunk driving is already illegal. But for teenagers and young adults, this cognitive ability changes slightly differently throughout the day.
Adolescents and young adults tend to sleep late, and cognitive abilities usually rise and peak later in the year. They were delayed by an average of two hours, reaching their peak in the afternoon. These findings were used to argue that "exams for adolescents, especially those who sleep very late, should be scheduled in the afternoon, not early in the morning".
However, the findings also raise an interesting question: given the effects of age on cognitive performance, adolescent teachers tend to be most cognitively strongest in the morning, when adolescent students are much less alert;In the afternoon, the teacher's cognitive abilities will decline and the students' cognitive abilities will peak. This mismatch results in most teachers and students not having the best classroom experience unless the teacher is very young or sleeps late.
Footage from the documentary "Scientific Sleep" (2006).
All of this illustrates the fact that our cognitive abilities are not fixed and change throughout the day. What's more, there are times in our lives when we need to use all the cognitive resources that our brains can mobilize. Everyone has to make a choice, and adults may be better suited to make their choice in the morning rather than in the early evening.
Now that we've talked about how cognitive abilities change throughout the day, let's turn our attention to the effects of sleep and circadian rhythm disruptions on three key cognitive factors (attention, memory, and executive function).
Attention and sleep and circadian rhythm disorders.
Attention is particularly susceptible to sleep deprivation. The 1986 Chernobyl nuclear power plant leak accident occurred at 1:23 a.m. and was caused entirely by human error. It was later discovered that the operators were severely sleep-deprived while working, unaware of the impending disaster facing the nuclear power plant. Over time, sleep deprivation can make our concentration, alertness, and ability to "perform tasks" greatly reduced.
For example, people who were able to sleep a full 9 hours per night for a week did not experience problems with decreased attention during subsequent study periods;People who slept 7 hours a night for a week experienced 5 episodes of inattention;People who slept 5 hours a night for a week experienced 7 episodes of inattention;Those who slept 3 hours a night for a week experienced 17 episodes of inattention. These findings suggest that even a slight reduction in sleep duration above optimal sleep can lead to concentration problems over time.
The 1986 Space Shuttle Challenger** is a typical example of "difficulty concentrating on complex problems". Post-disaster investigations have shown that cumulative sleep deprivation and sleep deprivation (causing difficulty concentrating and impaired executive function) caused staff to miscalculate when the shuttle lifted off.
The Exxon Valdez oil tanker spill was the result of a series of similar problems. The Alaska Oil Spill Commission's final report issued in 1990 noted that staff fatigue and chronic sleep deprivation were the main reasons for the 1989 grounding of the USS Exxon Valdez in Prince William Sound, which led to a massive oil spill.
Sleep deprivation can severely affect simple, repetitive tasks that require constant alertness. Several studies have shown that people are more likely to experience difficulty concentrating when performing monotonous tasks than when performing more complex tasks. This decreased alertness may result from involuntary brief "microsleep" episodes, which are interruptions of consciousness lasting 3 to 30 seconds. During this time, the person concerned was largely unresponsive and unaware that he had experienced micro-sleep.
Footage from the documentary "Scientific Sleep" (2006).
The brain's attentional mechanisms are closely related to our alertness, which stems from the excitatory neurotransmitters secreted by the brain. Alertness is a measure of how awake the brain is. Normally, the circadian system causes the brain to secrete more excitatory neurotransmitters during the day, providing an increasing drive for the body to stay awake throughout the day. In contrast to this circadian drive to keep people awake is the drive to sleep and the gradual accumulation of sleep stress, which itself reduces alertness and promotes sleep.
Normally, these two drivers are in balance, leading to the sleep-wake cycle. However, insomnia can increase sleep stress, causing sleep stress to build up, "canceling" the circadian drive to stay awake, resulting in a noticeable decrease in alertness. All in all, sleep deprivation can lead to decreased concentration, reduced alertness, and cognitive impairment.
In addition to reducing concentration, alertness, and overall vigilance, sleep deprivation can make cognitive performance erratic. And the closer to night and normal sleep time, the more erratic cognitive performance becomes. The body feels sleepy and tries to activate the stress center while increasing the secretion of excitatory neurotransmitters in the brain to maintain alertness. However, sleep at night is stressful, and the body moves from waking to sleep more quickly, which is dangerously unstable. One moment we seem to be concentrating, deluding ourselves into thinking we can get through it, and the next moment our attention suddenly slips away, which can be devastating.
Sleep deprivation makes people.
It's easier to remember negative information.
Memory is the brain's ability to recognize and store information over a period of time (days, months, years). Sleep is essential for consolidating new memories, and research has shown that the hippocampus in the brain is extremely important for the initial formation of new memories. When the brain picks up information, the hippocampus becomes neuroactive;During sleep, the pattern and sequence of neural activity in the hippocampus occur partially "replayed". This playback strengthens the connections between neurons and reinforces memories. Lack of sleep weakens hippocampal activity, which is directly related to the inability to recall new memories the next day. In contrast, sleep promotes hippocampal activity and memory formation.
There are three stages of memory: the first stage is encoding, that is, the formation of new memories after acquiring information, but this memory is easily forgotten;The second stage is consolidation, that is, the gradual "precipitation" of new memories into stable long-term memories;The third stage is retrieval, which is the recall of the consolidated memory. Consolidated memories are called long-term memories and fall into two categories. The first category is declarative memory, which refers to memories that are controlled by consciousness and can be recalled as facts and concepts. They are often referred to as "common sense", such as knowing the difference between a cat and a dog, or knowing that the author of the opera Der Ring des Nibelungen was the German Romantic composer Richard Wagner.
The second category is procedural memory, which refers to memories related to taking actions and developing skills. In simple terms, it's a memory of how to do something, such as riding a bike, tying your shoes, or cooking a Wellington steak. The distinction between declarative and procedural memory may be somewhat blurred, but the distinction is not just semantic.
During sleep, the two different types of memories also seem to be encoded differently. Several studies have shown that declarative memory is associated with slow-wave sleep, which is stored in the temporal lobe of the brain for a long time;Procedural memory, on the other hand, is associated with REM sleep and is stored in the cerebellum. It should be noted that REM sleep is not only related to procedural memory, but also to emotional memory, especially memory related to PTSD.
One of the key roles of sleep is to capture and consolidate new memories after a new experience. Interestingly, we have learned that sleep deprivation and the sleep state of the brain affect the type of declarative memory stored in the temporal lobe.
Footage from the documentary "Ten Laws of Sleep" (2010).
In a classic study, participants were divided into two groups, one group slept normally and the other group was not allowed to sleep for 36 hours, and each group had to memorize a series of words with different emotional colors. These words are negative (e.g., hate, war), positive (e.g., joy, happiness, love), and neutral (e.g., cotton). After two nights, both groups of subjects were asked what words they could recall. The total number of words recalled by the sleep-deprived group decreased by 40%, suggesting that sleep deprivation can greatly hinder memory acquisition.
The researchers also divided the words recalled by sleep-deprived subjects into three categories, including positive, negative and neutral, and found a surprising result: sleep-deprived subjects were able to recall significantly fewer positive words, while negative and neutral words were rarely forgotten. This suggests that a tired brain is more likely to remember negative rather than positive associative words. These and other research data clearly support the idea that sleep deprivation promotes the brain to acquire and store negative memories rather than positive ones. In other words, sleep deprivation can make people pay more attention to the negative information in the world.
So why do people forget positive associations but remember negative ones?Overall, in terms of mindset, humans seem to expect encounters with others, and by default they will have a pleasant experience, or at worst, a neutral experience. In contrast, negative behaviors or experiences are more unexpected and therefore more concerning. As a result, we usually give more attention to negative experiences.
The point is, a tired brain is more inclined to remember negative experiences than positive ones, which means that negative memories play a greater role in our judgment-making process. This can be useful in more often cases, as negative experiences are more likely to hurt us, so it's worth keeping in mind. However, problems arise when negative experiences dominate our worldview. In fact, one of the key characteristics of many mental illnesses is that there is a high level of negative bias.
There is also ample evidence that sleep not only contributes to the acquisition of declarative memory (recalling facts), but also participates in the acquisition of procedural memory, such as learning to complete a specific task. This is evidenced by many studies. In one study, researchers asked subjects to memorize a specific sequence of keys on a keyboard, each corresponding to a specific sound. After the learning period ended, the experiment entered a memory consolidation period, where the researchers divided the subjects into two groups, one group to sleep and the other group to stay awake. In the process of consolidating the memory, the researchers gave the subject** sounds associated with the correct sequence of keys in order to activate new memories in the brain.
The results showed that subjects who slept were more likely to recall the order of the keys they had learned. Many studies have shown that sleep deprivation inhibits the formation of programmed memories and reduces the ability to learn tasks.
A recent study showed that when subjects were completely deprived of sleep after learning to perform a task, their performance on the task deteriorated, and even afternoon naps or intensive exercises did not improve performance. This underscores the fact that staying up late and not sleeping can greatly impair task learning, and even naps or extra revision can't make up for it.
Get some sleep first and think about it tomorrow.
In addition to attention and memory, there is a third element of cognition: executive function, which is the ability to solve problems. Sleep not only helps with memory formation, but also helps us find new ways to solve complex problems. We are often told, "Get some sleep first, and think about it tomorrow." "My grandmother used to say that to me, and her instincts were always right. Remember, Grandma Rose's opinion on nightsocks is very ......"Sleep before you solve the problem" is not only highly regarded, but also hailed as a recipe for "insight". This is evidenced by many well-known cases.
Nobel laureate and pharmacologist Otto Loewi said he woke up and figured out how to experimentally verify that the brain's nervous system releases chemical transmittersScientist Dmitri Mendeleev said that he came up with the periodic table of chemical elements only after a good night's sleep;The German chemist August Kekulé, who pondered the arrangement of the atoms of the benzene molecule, fell asleep with questions and woke up recalling the Ouroboros in his dream and realizing that the benzene molecule was a ring made up of carbon atoms.
Footage from the documentary "Ten Laws of Sleep" (2010).
Waking up to a "flash of inspiration" doesn't just happen in science. In 1964, Beatles legend Sir Paul McCartney woke up to the melody of "Yesterday" taking shape in his head. "Yesterday" is the most covered song of all time, with more than 2,000 versions to date. I can't help but wonder how much economic benefit ...... this dream has bringed
So, in general, cognitive abilities allow us to gather information, store it, and respond appropriately. Again, cognition encompasses attention (which filters out secondary information), memory (memory formation), and proper executive functioning. Sleep is essential for these processes in the brain, and various sleep and circadian rhythm disorders can severely impair cognitive performance. Obviously, sleep is the best and safest "brain medicine" for human beings.
This article is published with permission from the publisher. Author: Russell Foster;Excerpt: Lotus;Editor: Wang Han Zhang Jin;Introductory proofreading: Liu Baoqing. Without the written authorization of the Beijing News, you are not allowed, welcome to the circle of friends. This article contains an advertisement for "The Scale of Time: 20 Years of the Beijing News's Best Books of the Year".