[BOOK] Matthew Walker - Why We Sleep

Question 1

What is a fragmented sleep? (how many times to wake up or how many minutes to be woken up?)

Answer 1

Intervene in fragmented sleep if you are waking up 6-7 times per night, or if wakeful periods are 20-25 minutes

Question 2

How many % of the total amount of time in bed is considered a healthy sleep?

Answer 2

Healthy sleep efficiency: of the total amount of time in bed, we want to be asleep approximately 85% or more asleep

Question 3

How many minutes after waking up to take the coffee?

Answer 3

It’s best to allow natural signals to wake up the body by delaying caffeine intake 90 minutes after rising

Question 4

What is the half-life of a caffeine?

Answer 4

Caffeine blocks adenosine receptors, thus reducing how much you feel the “sleep pressure.” If you ever drink coffee and then feel a crash later, this comes from caffeine wearing off while adenosine keeps increasing throughout the day.

Question 5

What the effects of alcohol on the sleep? (3 points)

Answer 5

• You lose consciousness quicker but are not achieving quality sleep
• Alcohol fragments sleep so you will wake up many times throughout and will not have continuous sleep
• Alcohol is a potent REM sleep blocker

Question 6

What is Melatonin and Adenosine? How long is a circadian rhytm?

Answer 6

• The circadian rhythm, regulated by melatonin (produced by the suprachiasmatic nucleus in the brain). Think of this as a natural “wake drive,” making you stay awake during the day and waning during night.
  
  • The circadian rhythm responds to light and darkness to calibrate itself. It’s naturally 24 hours and 15 minutes long on average.
• Adenosine is a fatigue signal and causes “sleep pressure.” This rises consistently through the day without sleep, making you feel more tired. Sleeping depletes adenosine, and you wake up with a lower level.

Question 7

Why we feel more awake in the morning then in the middle of the night (if we dont sleep)?

Answer 7

This explains an odd phenomenon: if you’ve ever had to pull an all-nighter, you might have noticed yourself getting a second wind in the morning, oddly feeling more awake at 8AM than at 3AM. This happens because the circadian rhythm “wake drive” is starting up again, and reduces the adenosine-circadian gap.

Question 8

Why are there morning and night persons? (from evolutionary point of view)

Answer 8

Circadian rhythms vary from person to person, depending on when they naturally wake up and have maximum energy. The idea of “morning people” and “night owls” is real.

• Whether you’re a morning or night person strongly depends on your genetics.
• Why would humans evolve with this variation? Evolutionarily, having a mixture of morning people and night owls allows a population to reduce its vulnerability in nighttime to a shorter period of time.
  
  • Example: As morning people sleep earlier (say at 10PM), night owls can keep up the watch. Then as night owls get tired (say around 4AM), the morning people are starting to wake.
    But in modern times, the night owls are heavily punished, since early work times force night owls to sleep and wake up earlier than they would naturally prefer. This reduces performance in the mornings. Furthermore, by the time night owls peak in the afternoon, the workday has already ended.

Question 9

What caffine is doing (blocking)?

Answer 9

Caffeine blocks adenosine receptors, thus reducing how much you feel the “sleep pressure.” If you ever drink coffee and then feel a crash later, this comes from caffeine wearing off while adenosine keeps increasing throughout the day.

Question 10

How many caffeine does a decaffeine coffee have?

Answer 10

Be careful when drinking decaf, as it apparently contains 15-30% of the caffeine in regular coffee - it’s nowhere near zero caffeine.

Question 11

When is jet lef the worst? Eastbound or westbound? Why?

Answer 11

Jetlag is usually worse when you fly eastbound because adjusting your schedule requires falling asleep when the body wants to be awake. This is more difficult than staying awake when your body wants to sleep.
Since the circadian rhythm is slightly longer than a day, lengthening it is easier than shortening it.

Question 12

How do you know if you have a sleep deficit? Here are a few signs:

Answer 12

• You don’t wake up naturally at the time you set your alarm - this means your body wants more sleep.
• When you read, you often lose track and need to read a sentence twice.
• You feel drowsy just a few hours after waking.
• You need coffee to feel functional.

Question 13

What’s happening during rem and non-rem sleep?

Answer 13

In summary, your brain switches between two types of sleep - REM (rapid eye movement) and non-REM (NREM) sleep. The two types of sleep have different functions - simplistically:

• NREM clears out old memories and mental “trash,” and it moves information into long-term storage.
• REM strengthens the valuable connections that remain, and it forges creative novel connections.

Question 14

What’s the ratio between rem and non-rem sleep?

Answer 14

In total for a single night, there’s about an 80/20 split between NREM/REM sleep.

Question 15

How long a sleep cycle lasts?

Answer 15

When you sleep, your brain goes through sleep cycles that each last about 90 minutes. Each sleep cycle generally begins with NREM sleep, then ends with REM sleep. As one cycle ends, the next begins. You can see this in a sleep graph here:

Question 16

Earlier in the night - which kind of sleep does the body prefer?

Answer 16

The author hypothesizes that it’s like making a sculpture out of a mass of clay. Earlier in the night, more NREM is needed to clear out junk memories that aren’t useful anymore. Then once only the useful stuff remains, REM strengthens what’s left.

(Shortform note: One way to think about this is that an animal might be interrupted in the middle of the night. So if an animal could only sleep 3 hours in one night, it’d make sense for the more critical functions to be performed first, with the later functions being a luxury if the animal could sleep a full night. This may suggest that NREM performs a more vital function for survival.)

Also, beware of what this means for cutting your sleep short. If you normally sleep 8 hours, and one night you have to cut sleep to 6 hours, then you’re not just losing 25% of sleep - you might be losing 60-90% of your REM sleep!

Likewise, going to sleep later than usual might cut short your NREM sleep.

Question 17

Are we sleeping in REM or nREM sleep?

Answer 17

REM sleep looks like awake activity, and it’s where dreams happen. A few odd things happen during REM sleep:

• Your sense of time in dreams seems dilated - an hour may seem to pass when in reality only 5 minutes have.
• Unlike the rest of sleep, you consciously perceive your senses, like sight and sound. In non-REM sleep, the thalamus in your brain blocks you from consciously perceiving senses. Once REM sleep starts, this blockade is released.
• In REM sleep, your eyes move rapidly This was initially thought to be visual exploration of the dream field, but this turns out to be more related to the creation of REM sleep than passive observation of it.

Question 18

If REM sleep looks like wakefulness, how can an observer distinguish someone who’s dreaming from being awake?

Answer 18

Muscle atonia - during REM sleep, your voluntary muscles are completely limp. Your brain does this to prevent you from acting out your dreams, since fighting an enemy might cause you to accidentally punch your surroundings.

Question 19

if wakefulness is damaging to the body and sleep recovers it, why did life ever bother to wake up?

Answer 19

of course, you can’t be productive and reproduce when sleeping, so sleeping too much would be evolutionarily disadvantageous.

Question 20

How long animals sleep? does it depends on the size or characteristics of the animal?

Answer 20

The amount of sleep per day varies from 4 hours in elephants to 19 hours in bats. There are no strong correlations between animal characteristics and amount of sleep, though within animals of a similar size, a more complex brain increases sleep.

Question 21

Do all animals have REM sleep?

Answer 21

Among animals, REM sleep occurs only in birds and mammals. Because REM evolved independently in these two distant evolutionary trees, REM likely performs a critical function that NREM cannot accomplish, or that REM is more efficient at accomplishing.

Question 22

Who sleep more? Human or apes? Why is it like that?

Answer 22

Relative to great apes, humans sleep less (8 hours in humans vs 10-15 hours in apes) and have more intense REM sleep (20% in humans vs 9% in apes). Matthew Walker hypothesizes this evolved as follows:
Apes sleep in trees and enjoy great safety at night.
- In the human ancestor Homo erectus, an upright body posture and shorter arms made sleeping in trees more difficult. REM sleep is also dangerous in trees because limp muscles increases the risk of falling out.
- Discovery of fire allowed humans to ward off predators and parasites at night. But danger still inevitably lurked, so humans who could sleep more efficiently for less time were evolutionarily selected for.
- Then as human societies became more complex, REM sleep became more important. REM sleep is found to be critical for 1) internal emotion regulation, 2) reading emotions from others, 3) creativity. This led to improved survival strategies and larger social groups, which further increased brain complexity and more need for REM sleep, forming a positive feedback loop.

Question 23

Why fetuses (babies in the womb) kick and punch? (no muscle-atonia?)

Answer 23

Fetuses spend almost all of the time in a sleep-like state. It doesn’t yet have the part of the brain that causes muscle-atonia during sleep, thus explaining why babies in the womb kick and punch.

Question 24

During the last 2 weeks of pregnancy, how many REM sleep in fetuses? Why?

Answer 24

During the last 2 weeks of pregnancy, REM sleep in fetuses ramps up to 12 hours a day. This causes rapid synaptogenesis and building of neural pathways throughout the brain. In experiments with rat fetuses, disturbing REM sleep stalls construction of the cerebral cortex.

Question 25

Alcohol effect on REM sleep in fetuses?

Answer 25

Alcohol impedes REM sleep in fetuses and babies, causing abnormal synaptogenesis. Once disrupted, a fetal brain may never fully regain normal function.

Newborns of alcoholic mothers spend far less time in REM sleep.

2 drinks reduce REM sleep and breathing rate in unborn infants.

When babies drink milk containing alcohol, their REM sleep reduces by 30%.

Because REM sleep is involved in emotional recognition and social interaction, disrupting REM sleep in utero might contribute to the autism spectrum.

• Autistic people show 30-50% less REM sleep than normal.
• Rats deprived of REM sleep develop into socially withdrawn adults.

Question 26

When do babies start showing sleep patterns? circardian rhytms?

Answer 26

While starting with very irregular sleep, babies eventually show more regular sleep patterns starting at 4 months, as their suprachiasmatic nucleus and circadian rhythm develop.

Question 27

Can child drink coffee?

Answer 27

Caffeine exposure during childhood could reduce NREM sleep, delaying brain maturation and learning.

Question 28

What are the biological clocks in teenagers? Asking adult to sleep at 7pm is like asking teenager to sleep at … pm?

Answer 28

In puberty, teens develop a later biological clock than adults, preferring to stay up later and wake later. This isn’t just teens being rebellious - it’s in their biological nature. Asking teens to sleep at 10PM is like asking adults to sleep at 7PM.

The author theorizes that this is evolutionarily helpful for teens to gain independence from their parents (having time to be awake while their parents are sleeping). Moreover, teens do so collectively, and so they get private time to socialize.

The author theorizes that this is evolutionarily helpful for teens to gain independence from their parents (having time to be awake while their parents are sleeping). Moreover, teens do so collectively, and so they get private time to socialize.
Unfortunately, in the modern day, schools start at a very early hour (largely to match the circadian rhythms of adult parents). It’s far out of sync with the natural circadian rhythm of teens, so they tend to sleep late and wake up far earlier than they naturally would.

Question 29

When the sleep starts to deteriorate? In our late 40s, how many deep sleep we lost comparing to a teenager? and what about in the age of 70?

Answer 29

Sleep quality starts deteriorating in the late 20s, with deep NREM sleep becoming impaired in length and power. In your late 40s, you’ll have lost 70% of deep sleep as a teenager; by 70, you’ll have lost 90% of deep sleep. Unfortunately, less NREM sleep worsens the ability to cement new memories in older people.

You often hear of the elderly sleeping little at night, so the natural conclusion is that the elderly just need less sleep. But this could be a myth. The elderly might be sleeping less because they’re unable to sleep for as long. This means they could still benefit from more sleep.

Question 30

Why older people have a bad sleep? and feel less energetic?

Answer 30

We’re generally unable to determine our sleep quality after sleeping. So when seniors sleep poorly and feel unhealthy, they don’t realize they need to improve their sleep quality. They chalk it up to insomnia.
Because the elderly sleep poorly, they feel tired during the day, and they doze off in the early evening. Unfortunately, this reduces the adenosine sleep pressure at night, which causes them to have trouble falling asleep later. Then, their early circadian rhythm wakes them up before they can get a full night’s rest. This causes a vicious cycle of poor sleep.

All this causes lower sleep efficiency - people in their 70s have 80% sleep efficiency, meaning they stay awake in bed for 1.5 hours when trying to sleep 8.

Question 31

What can elderly do to have a better sleep?

Answer 31

There are a few ways to get around this:

• Melatonin helps strengthen the desire to sleep in elderly people. It reduces time to falling asleep and improves reported sleep quality.
• Seniors who want to push their circadian rhythm back should get bright-light exposure in the late afternoon, not in the mornings.

Question 32

Sleep improves long-term factual recall - what’s hapenning in the brain? What hippocampus and cortex do?

Answer 32

Your brain stories different memories in different places. The hippocampus stores short-term memory with a limited capacity; the cortex stores long-term memory in a large storage bank.

The slow-wave, pulsating NREM sleep moves facts from the hippocampus to the cortex. This has two positive effects: 1) it secure memories for the long term, and 2) it clears out short-term memory to make room for new information and improves future learning.

Have you ever woken up recalling facts that you couldn’t have recalled before sleeping? Sleep may make corrupted memories accessible again.

While good sleep improves memory, sleep deprivation can prevent new memories from being formed. In part, this might be because the hippocampus becomes less functional with less sleep, partially because lack of NREM sleep prevents solidifying of new memories.

Unfortunately, making up a sleep deficit later doesn’t help recover a previous days’ memory - if you lost it, you’ve lost it.

Question 33

3 main brain benefits of sleep?

Answer 33

1) Sleep improves long-term factual recall
2) Sleep prunes memories worth forgetting
3) Sleep increases “muscle memory” or motor task proficiency

Question 34

what is more important to get brain benefits? REM or nREM sleep?

Answer 34

The above benefits generally occur in NREM sleep, which is concentrated in the beginning of sleep. In experiments, participants who have NREM sleep disrupted perform worse than those who have REM sleep disrupted.

A few last scientific details:

• Motor memory is associated with stage 2 NREM, which is concentrated in the last cycle of sleep.
• Sleep spindles are associated with better memory effects.

Question 35

How Sleep Deprivation Harms the Brain? (3 points)

Answer 35

1. Sleep Deprivation Worsens Attention and Concentration
2. Sleep Deprivation Worsens Emotional Control
3. Sleep Deprivation May Contribute to Alzheimer’s

Question 36

Driving after having slept less than 4 hours increases crash risk by … x. (how many times)

Answer 36

Driving after having slept less than 4 hours increases crash risk by 11.5x.

Question 37

Being awake for … hours (being past your bedtime by 3 hours) is as cognitively impairing as being legally drunk. (how many hours)

Answer 37

Being awake for 19 hours (being past your bedtime by 3 hours) is as cognitively impairing as being legally drunk.

Question 38

Having 10 nights of 6-hour sleep is equal in damage to one all-nighter, as is 6 nights of 4-hour sleep. True?

Answer 38

Sleep deficits add up over time, and performance progressively worsens with greater sleep deficit. Having 10 nights of 6-hour sleep is equal in damage to one all-nighter, as is 6 nights of 4-hour sleep.

Question 39

Why does sleep cause more accidents?

Answer 39

Part of it is delayed reaction time. Another part is a “microsleep,” where your eyelids shut for just a few seconds and you go unconscious and lose motor control. If you’re in a car going 60 mph, falling asleep for just a few seconds could result in a terrible accident.

Sleep deprivation is an insidious problem because when you’re sleep-deprived, you don’t know how poorly you’re performing. (This is like being drunk and thinking you’re far more capable of doing things than you actually are). And if you’re chronically sleep-deprived, your low performance becomes a new normal baseline, so it’s hard for you to see just how badly you’re performing.

Question 40

How many % of people can sleep for 6 hours and still be perfectly fine?

Answer 40

Think you can do just fine on 6 hours of sleep? Chances are, you can’t. Less than 1% of the population is able to get six hours of sleep and show no impairment (this is largely genetic and relates to the BHLHE41 gene). Everyone else is just fooling themselves and propping up their energy with caffeine.

And think you can get by with power naps? They only get you partway there - power naps are most effective at the onset of fatigue, not when you’re already sleep-deprived.

Question 41

why are we more emotional when we are sleep deprived? (what’s hapenning in the brain?

Answer 41

The amygdala is the part of your brain responsible for emotions like fear and anxiety. Normally, it’s held in check by your prefrontal cortex (the rational part of your brain). But when you’re sleep-deprived, this suppression is weakened, and your amygdala can run amok, leading to 60% more emotional reactivity. The highs can be higher, and the lows lower.

On the other side of fear and anxiety, positive rewards and dopamine may be amplified by sleep deprivation too. Therefore, sleep deprivation can intensify sensation-seeking, risk-taking, and addiction.

Question 42

mental illness - connection with sleep?

Answer 42

More gravely, sleep may play an important role in mental illness. Here’s suggestive evidence:

• Sleep disruption is a common symptom of all mood disorders. The causation is unclear: does bad sleep cause mood disorders, or do mood disorders cause bad sleep, or both? But the author believes sleep plays at least some aggravating role.
• One night of sleep deprivation can trigger a manic or depressive episode in bipolar patients.
• Sleep deprivation is associated with suicidal ideation in teenagers.
• Surprisingly, sleep deprivation makes ⅓ of depression patients feel better, possibly by amplifying their positive emotions. However, it makes ⅔ feel worse, so it isn’t prescribed as a treatment.

Question 43

Why NREM can have connection with Alzheimer?

Answer 43

Frontal lobe degeneration (especially through Alzheimer’s characteristic amyloid plaques) disrupts NREM sleep.
Lack of NREM sleep disrupts memory formation, a key symptom of Alzheimer’s.
(Notably, the hippocampus is not affected by amyloid plaques, presenting a conundrum to scientists on why memory is disrupted in Alzheimer’s.)

Lack of NREM sleep disrupts the lymphatic cleanup system, during which glia shrink to less than half their normal size and amyloid plaques are cleared out more readily.

It’s easy to see how a vicious cycle can occur - frontal lobe degeneration disrupts NREM sleep, which causes further frontal lobe degeneration.
Sleep loss precedes Alzheimer’s by several years, suggesting this could be an early diagnostic.

Encouraging NREM sleep, through artificial brain stimulation if needed, might be therapeutic for Alzheimer’s. It could also be prophylactic, the same way statins protect against heart disease.

Question 44

A population study showed that shorter sleep was associated with a … % increased risk of developing heart disease. (how many?)

Answer 44

A population study showed that shorter sleep was associated with a 45% increased risk of developing heart disease.

An interesting finding: daylight savings time is a natural sleep experiment that typically increases or decreases sleep by 1 hour. When the clock moves forward and the population gets 1 less hour of sleep, there is a significant spike in heart attacks and traffic accidents.

Question 45

In an experiment, after 4 hours of sleep a night for 6 nights, subjects were … less effective at absorbing a standard dose of glucose.

Answer 45

Sleep deprivation reduces insulin responsiveness, which causes hyperglycemia.

In an experiment, after 4 hours of sleep a night for 6 nights, subjects were 40% less effective at absorbing a standard dose of glucose.

In a population study, those sleeping < 6 hours a night showed higher rates of T2D (after controlling for body weight, alcohol, smoking, and other factors).

Question 46

Why sleep deprivation cause weight gain?

Answer 46

Hormonally, reduces leptin (the hormone that makes you feel full) and increases ghrelin (the hormone makes you feel hungry). It becomes harder to feel satisfied after eating.

Increases endocannabinoids (reduces pain sensation but increases appetite; also released in runner’s high), which increases eating

Makes you feel lethargic, which makes you less likely to exercise

Disrupts the linkage between the rational prefrontal cortex and the primal appetite center in the brain (similar to emotional control in the last chapter), so it becomes harder to regulate your eating

Question 47

In an experiment, subjects were randomized into a normal 8-hr sleep group, and a low 4-hr sleep group. Both groups were carefully monitored and controlled for physical activity.

The low-sleep group ate ???…??? more calories each day, even after just 4 days of sleep deprivation.

Answer 47

In an experiment, subjects were randomized into a normal 8-hr sleep group, and a low 4-hr sleep group. Both groups were carefully monitored and controlled for physical activity.

• The low-sleep group ate 300 more calories each day, even after just 4 days of sleep deprivation.
• The low-sleep group was also more prone to overeating each meal, consuming 330 more calories in snack foods after a meal.

One might argue that decreased sleep naturally causes more calorie burn, but an all-nighter actually consumes only 147 more calories than sleeping. Sleep is metabolically more intense than you might guess.

Question 48

Finally, if you’re losing weight and under sleep deprivation, the shift of where you lose the weight from differs.

When sleep-deprived, … % of weight loss comes from lean body mass like muscles, compared to under … % with plentiful sleep.

Answer 48

Finally, if you’re losing weight and under sleep deprivation, the shift of where you lose the weight from differs.

When sleep-deprived, 70% of weight loss comes from lean body mass like muscles, compared to under 50% with plentiful sleep.

Question 49

Reproductive system:

In males, sleep deprivation decreases

1. …
2. …
3. …

Answer 49

In males, sleep deprivation decreases testosterone, testicle size, and sperm count.

Question 50

Experimentally, the is acute - 5 hours of sleep for one week “ages” a man … years by testosterone

Answer 50

Experimentally, the is acute - 5 hours of sleep for one week “ages” a man 10-15 years by testosterone

Beyond libido, testosterone also governs bone density and muscle mass.

Question 51

What causes sleep deprivation at women?

Answer 51

In females, sleep deprivation reduces follicular-releasing hormone (necessary for conception), increases abnormal menstrual cycles, and causes more issues with infertility.

Your face is rated as less attractive and less healthy after one night of short sleep. So there might be something to the idea of “beauty sleep.”

Question 52

In an experiment, subjects exposed to low sleep over 1 week were …% likely to develop a cold when exposed to a virus, vs 18% in the normal-sleep group.

Answer 52

Sleep deprivation reduces your ability to ward off infectious disease:

• In an experiment, subjects exposed to low sleep over 1 week were 50% likely to develop a cold when exposed to a virus, vs 18% in the normal-sleep group.
• Sleep deprivation reduces the immune response to flu vaccines by over 50%.
• Sleep deprivation reduces circulating levels of natural killer cells .

Question 53

Sleep deprivation increases inflammation, which increases cancer severity:

1. …
2. …
3. …

Answer 53

Sleep deprivation increases inflammation, which increases cancer severity:

• Promotes angiogenesis, or blood vessel development
• Promotes lability of cancer cells, leading to metastasis
• Downregulates M1 macrophages and upregulates M2 macrophages, both changes increasing cancer risk.

Population studies show a link between nighttime shift work and risk of cancer (common occupations include nurses and pilots).
In response, Denmark now pays worker comp to women who developed breast cancer after doing night-shift work in government-sponsored jobs

Question 54

Why sleep deprivation can cause faster ageing?

Answer 54

Telomeres are a component of DNA, and they get shorter with aging. Sleep deprivation has been shown to hasten telomere shortening, thus implying an increase in aging.

Question 55

why would animals evolve so that sleep deprivation causes all these bad issues

Answer 55

(Shortform note: why would animals evolve so that sleep deprivation causes all these bad issues? Evolutionarily, consider that these responses might promote survival: in caveman days, times of low sleep may mean conditions that threaten survival (low food stores, tough weather, hostility with another tribe). The above responses might promote short-term survival - hoarding calories, activating the “fight-or-flight” system, decreasing reproduction - at the expense of long-term well-being.)

Question 56

In which phase vivid dreaming happens?

Answer 56

Most vivid dreaming happens during REM sleep (though NREM sleep has some vague non-vivid dreaming, like “I was thinking about clouds”).

During REM dreaming, your visual, motor, memory, and emotional areas of the brain are active. Your prefrontal cortex (governing rationality) is muted.

Question 57

How the technology can find out what we are dreaming about?

Answer 57

Interesting: it may be possible to predict what you’re dreaming about through fMRI.

• To build a profile of your brain, you look at different images while awake, and the fMRI signature is captured.
• Then as you dream, your dreaming fMRI is matched to your awake fMRI profiles, predicting what you’re currently looking at while dreaming.

Question 58

We often think about the meanings of our dreams. Do dreams merely replay events of the day, or do they reflect our emotional concerns?

Answer 58

• A study showed that only a small fraction (1-2%) of dreams replay the literal events of the day.
• A greater fraction of dreams (~45%) reflect our underlying emotional worries we have while awake.

Question 59

Why we can look back at painful memories without feeling the original full emotional intensity? Thanks to REM sleep.

Answer 59

REM dreaming reduces pain from difficult emotional experiences. The brain seems to reprocess upsetting memories and emotional themes, retaining the useful lessons while blunting the visceral emotional pain. This might be why we can look back at painful memories without feeling the original full emotional intensity.

Interestingly, dreaming about the upsetting content itself, or its emotional themes, is necessary to have this emotional blunting effect. REM sleep by itself does not.

How might this happen? In REM sleep, the stress hormone norepinephrine in your brain is reduced to zero, which possibly allows the brain to process upsetting memories in a “safe” brain environment. In fact, REM sleep is the only time that norepinephrine is absent from your brain.

In an experiment, subjects were shown a series of emotionally triggering images two separate times, separated by ~12 hours. One group saw set 1 before sleeping and set 2 after sleeping. The other group saw both on the same day without sleeping, set 1 in the morning and set 2 at night. The former group reported much less emotional disturbance upon seeing the images the second time, suggesting sleep had blunted their emotional reaction.

Question 60

How a lack of REM sleep can influence understanding of other people’s emotions?

Answer 60

Sleep deprivation reduces your ability to interpret subtle facial expressions. Sleep-deprived people more often interpret faces as hostile and aggressive.

Suggestive evidence: people on the autism spectrum have disrupted REM sleep. They also have issues reading people’s facial expressions

Suggestive evidence: people on the autism spectrum have disrupted REM sleep. They also have issues reading people’s facial expressions