Why We Sleep by Matthew Walker

Inadequate sleep, even with moderate reductions for just one week, disrupts blood sugar levels to the point of being considered pre-diabetic. Lack of sleep increases the likelihood of blocked and brittle coronary arteries, putting you at risk for cardiovascular disease, stroke, and congestive heart failure. - **Perhaps you've noticed that you tend to eat more when you're tired?** This is because lack of sleep increases the levels of a hunger hormone and decreases a hormone that signals food satisfaction. This leads to weight gain in adults and children who don't get enough sleep. Additionally, if you try to diet without enough sleep, it's pointless because you'll mostly lose lean body mass, not fat. <aside> 🗣 The shorter your sleep, the shorter your life span. </aside> - **Sleep Benefits:** - **Sleep** improves many functions, such as *learning, memory, and decision-making*. - **Sleep** also helps maintain our psychological well-being by *adjusting our emotional brain circuits, enabling us to handle social and psychological challenges calmly the next day.* - **Sleep** benefits our immune system *by preventing illness and fighting cancer*. It also helps *regulate our metabolism, appetite, and weight*. **Adequate sleep** is important for *a healthy gut and cardiovascular system, maintaining blood pressure and heart health.* - **Dream benefits:** **Dreaming** offers various benefits to all species, including humans. These benefits include - *a soothing chemical release that alleviates painful memories* and - *a virtual reality environment where the brain combines past and present knowledge, fostering creativity*. **What about Exercise and Diet vs Sleep?** A healthy diet and exercise are important, yes. But we now recognize that sleep is a crucial element in overall health. The adverse effects on the body and mind from one night of inadequate sleep surpass those from skipping a meal or forgoing exercise. It is difficult to conceive of any other condition—whether natural or induced by medical means—that exerts such a profound influence on both physical and mental well-being. The chapters are written in a logical order, traversing a narrative arc in four main parts: 1. Explains sleep in a simple way: 1. what it is, 2. what it isn't, 3. who sleeps, 4. how much they sleep, 5. how humans should sleep (but don't), 6. and how sleep changes throughout life, for better and for worse. 2. Details the good, the bad, and the deathly of sleep and sleep loss. 1. benefits of sleep for brain and for body. 2. the impact of insufficient sleep on health, disease, and mortality—a clear reason to prioritize sleep. 3. Offers safe passage from sleep to the fantastical world of dreams scientifically explained. 1. The question of whether or not dream control is truly possible, and whether it is advisable, will be answered. 4. seats us at the bedside and provides an explanation of various sleep disorders, including insomnia. 1. Exploring the reasons why many individuals struggle to achieve restful sleep on a consistent basis. 2. Engage in an honest discussion about sleeping pills, drawing from scientific and clinical data rather than relying on hearsay or marketing messages. 3. Provide information on new, safer, and more effective non-drug therapies for improving sleep. 4. Moving beyond the individual level, we will then delve into the significant impact that inadequate sleep has on education, healthcare, and business. 5. The evidence presented challenges the notion that sacrificing sleep for extended waking hours is an effective, safe, profitable, or ethical approach in any of these fields. ***Time Dilation and what we learned from a baby in 1952.*** - **SELF-IDENTIFYING SLEEP** **How would you know if somebody else is a sleep?** (Jessica vignette) 1. Organisms assume a typical position while sleeping. Land animals often lay horizontally, like a baby on the couch. 2. Sleeping organisms exhibit reduced muscle tone, especially evident in postural relaxation. 3. Sleeping individuals are unresponsive and do not communicate. 4. It's reversible, unlike coma, anesthesia, hibernation, or death. Remember, Jessica woke up when the item fell. 5. Sleep follows a reliable 24-hour pattern, guided by the circadian rhythm. **How do we know that we have slept?** 1. You frequently self-assess your sleep. Every morning, you wake up aware that you have been asleep. 2. This self-assessment of sleep is so sensitive that it can measure the quality of your sleep. 3. A personal assessment different from signs used to evaluate others' sleep. **Universal indicators:** 1. The loss of external awareness means you stop consciously perceiving your surroundings. Except for your 5 senses. seeing, listening, taste, smell, touch. The *thalamus* blocks sensory signals, preventing their progression to the cortex. 2. The self-determined judgment of sleep involves experiencing time distortion in two conflicting ways. The sensation of a time gap assures you that you've slept. Checking how long you have slept for in airplane. Maybe you had an early flight and set your alarm for 6:00 a.m. However, you woke up at 5:58 a.m., just before the alarm. ***It seems your brain can track time precisely, even when asleep.*** In dreams, time is often stretched. Think about the last time you snoozed your alarm. You fall back into a dream for five minutes, but it feels like an hour. Unlike non-dreaming sleep where time awareness is lost, in dreams, time is sensed but not accurately—it's usually elongated. **Dreams:** Rapid eye movement (REM) sleep, the main stage for dreaming. - **AN INFANT REVELATION—TWO TYPES OF SLEEP (you can skip)** - **How do they study sleep? (not important, skip)** The best way to scientifically confirm sleep involves recording signals from three areas: (1) brain activity, (2) eye movement, and (3) muscle activity. These signals are collectively called "polysomnography" (PSG). In 1952, Eugene Aserinsky at the University of Chicago documented infants' eye movements during sleep, noting periods of rapid side-to-side darting. these sleep phases were always accompanied by remarkably active brainwaves, almost identical to those observed from a brain that is wide awake. Sandwiching these earnest phases of active sleep were longer swaths of time when the eyes would calm and rest still. During these quiescent time periods, the brainwaves would also become calm, slowly ticking up and down. These sleep phases featured active brainwaves, similar to an awake brain. They were interspersed with calm periods, where the eyes and brainwaves would rest. Kleitman and Aserinsky made a profound discovery: humans cycle through two types of sleep, NREM (non-rapid eye movement) and REM (rapid eye movement). NREM sleep was later divided into four stages, named NREM stages 1 to 4, each increasing in depth. Stages 3 and 4 are the deepest, defined by the increased difficulty in waking an individual from them, compared to stages 1 or 2. - **THE SLEEP CYCLE, *REM vs NREM* (complex, you can skip.)** NREM and REM engage in a recurring cerebral battle every ninety minutes throughout the night. The vertical axis displays brain states: Firstly Wake, followed by REM sleep, and the decreasing stages of NREM sleep, stages 1 to 4. The horizontal axis represents nighttime, from eleven p.m. to seven a.m. This graph is called a hypnogram.  We alternate between NREM and REM sleep every ninety minutes throughout the night, but the ratio of NREM to REM sleep within each cycle varies significantly. In the first half of the night, most of our ninety-minute cycles are filled with deep NREM sleep and minimal REM sleep. However, in the second half, the balance shifts towards REM sleep dominating, with little to no deep NREM sleep. - Why did Mother Nature design this strange, complex equation of unfolding sleep stages? - Why cycle between NREM and REM sleep over and over? - Why not obtain all of the required NREM sleep first, followed by all of the necessary REM sleep second? Or vice versa? Deep NREM sleep, prevalent early in the night, weeds out unnecessary neural connections. Contrastingly, REM sleep, dominant later, strengthens these connections. The sleep cycle begins with NREM sleep, followed by REM sleep, a fact many are unaware of. If you go to bed at midnight but wake up at six a.m., you'll lose 25% of total sleep time, but 60-90% of REM sleep which is concentrated in the latter part of the sleep cycle. The same happens if you go to bed late, you'll lose significant NREM sleep. Just like an unbalanced diet, depriving the brain of NREM or REM sleep, both crucial for different brain and body functions, leads to physical and mental health issues. Burning the candle at both ends with sleep doesn't work. - **HOW YOUR BRAIN GENERATES SLEEP** What is the nature of your brainwaves as you sleep? How distinct would these patterns of brain activity be, compared to the ones you're experiencing as you read this sentence, fully awake? Can these varying electrical changes in the brain clarify why you are conscious in one state (wakefulness), non-conscious in another (NREM sleep), and in a state of dream-consciousness in the third (REM sleep)?  *Various areas of your waking brain process diverse information at different times and in different manners.* These brainwaves are not just fast, but also unpredictable. Imagine a stadium full of people, each representing a brain cell, and a microphone overhead, representing an electrode. Before a game, the crowd's chatter is much like the disorganized activity of neurons processing different information, resulting in chaotic brainwaves. *When you sleep, this changes. You first enter light NREM sleep, followed by deeper stages known as "slow-wave sleep."* *The brainwave activity slows down, becoming more unified, almost ten times slower than when awake.* **The synchronous and predictable slow waves of NREM sleep contrast with your waking brain activity**. If converted into sound, you could rhythmically move to the pulsing measure of your NREM sleep. <aside> 🧲 Extra notes: 1. Individuals with more frequent and powerful sleep spindles are more resistant to external noise disturbances during sleep. 2. Often, it's hard to tell REM sleep from wakefulness using only brainwave activity. </aside> - **Considerations** REM vs AWAKE **During REM sleep, signals of emotions, motivations, and memories are projected in our sensory cortices, creating a nightly theater of bizarre, autobiographical themes**. **Wake state is about reception, experiencing the world. NREM sleep is reflection, storing new facts and skills.** **REM sleep is integration, interconnecting these new elements with past experiences and building an accurate model of the world, fostering innovative insights and problem-solving abilities.** --- INVOLUNTARY MUSCLES The termed "*atonia*" refers to **the absence of muscle tone during REM sleep.** It is triggered by a disabling signal from the brain stem to the spinal cord, causing body muscles to lose all tension and strength. In effect, you become an embodied prisoner, immobilized by REM sleep. However, this physical captivity ends as the REM-sleep phase concludes. The dissociation during dreaming, where the brain is active but the body is immobilized, distinguishes REM-sleep brainwaves from wakeful ones. Why did evolution decide to outlaw muscle activity during REM sleep? Evolution discontinued muscle activity during REM sleep to prevent individuals from physically acting out their dreams, which are rich with movement due to the constant motor commands in the brain. How do we confirm the occurrence of movement commands during dreams without relying on someone's recollection of a running or fighting dream? Unfortunately, some people, especially later in life, may experience a failure in the paralysis mechanism, leading to the conversion of dream-related motor impulses into actual physical actions.