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Why do we need to close eyes to sleep?

Why do we need to close eyes to sleep?


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Out of all our sensory organs, we need to stop taking signals explicitly only from eyes in order to sleep. Even interestingly, those who are not able to receive signals from eyes (i.e., the visually challenged people) also need to close their eyes in order to sleep. I wonder what is the relation of closing eyes with sleeping. I think the reason might be related to the state of the muscles related to the eyes. Of course, even if it were the case that one could keep her eyes open while sleeping, the brain would stop paying attention to the signals received by the eyes -- just like the brain stops paying much attention to the signals received by the nose or the ears while sleeping even if these organs are not physically closed or prevented from receiving signals. But in the case of the eyes, they are physically closed while sleeping, which makes me curious.


Unlike our underwater ancestors, land animals have evolved eye lids or nictitating membranes to protect our eyes and keep them moist periodically by blinking. During the sleep state, closing our lids protects the eyes from drying out and getting damaged while unconscious. In addition to the lids themselves blocking light stimulus (not totally), our eyes also roll back to attenuate light stimulation. Fish also sleep and don't need eyelids to do so, thus closing eyes is not a prerequisite for the sleep state.

Textbook Source: Butler, Ann B.; Hodos, William (2 September 2005). Comparative Vertebrate Neuroanatomy: Evolution and Adaptation. John Wiley & Sons. p. 215. ISBN 978-0-471-73383-6.


How Sleep Works

Sleep is an essential function of the human body, necessary for maintaining physical and mental health. This complex biological process (1) has innumerable benefits, including helping us learn and integrate new information, allowing time for the body to repair damaged cells and tissues, and helping us to fight infections.

Getting enough sleep can help you feel more rested, become more optimistic, and improve your relationships (2). While learning about the science of sleep isn’t a requirement for getting quality rest, many people find it enlightening to learn about what happens when they fall asleep at night.

The Sleep-Wake Cycle

The sleep-wake cycle is the body’s natural rhythm of alternating periods of sleep and wakefulness (3). The brain regulates the sleep-wake cycle through an intricate system that receives input from two sources (4): the body’s sleep drive and the circadian clock.

  • Sleep Drive: The pressure to sleep builds the longer we stay awake. Once we fall asleep, sleep pressure dissipates until we wake up and the process begins again. The amount of sleep drive we accumulate also affects how long we sleep and sleep intensity (5). The sleep drive explains why we sleep longer and more deeply after periods of sleep deprivation.
  • Circadian Clock: A central clock in the human brain organizes many daily rhythms in our bodies and behaviors (6). Circadian rhythms are 24-hour cycles (7) that influence our desire to sleep during one part of the day and stay awake at another. These cycles are impacted by our environment, which is one reason why our ability to fall asleep is affected by factors like light and temperature.

Sleep Phases

When a person falls asleep, the body begins cycling through two alternating sleep phases: rapid eye movement (REM) sleep and non-rapid eye movement (non-REM) sleep. The body cycles through these phases several times a night, with each cycle lasting for around 80 to 100 minutes (8):

Non-REM Sleep

The non-REM phase of sleep is vital for memory formation. In fact, missing this phase of sleep can cause a person’s ability to learn new things to decrease by up to 40% (9). Accounting for around 80% of the time we spend asleep (10), non-REM sleep includes three stages:

  • Stage 1: The first stage of sleep lasts several minutes. During this short period of light sleep, a person’s heart rate and breathing slows as the muscles of the body relax.
  • Stage 2: A person is still transitioning to deeper sleep while in the second sleep stage. During this stage, heart rate, breathing, and muscles continue to relax. Interestingly, this stage is where we spend the most time during sleep.
  • Stage 3: In the third stage of non-REM sleep, heart rate and breathing drop to their lowest levels of the night. This sleep stage is an important time for restoring energy and allowing the body to grow and heal.

REM Sleep

The body usually enters the REM phase around 90 minutes after falling asleep. During this phase of sleep, heart rate and breathing increase to levels near those seen while a person is awake. Most muscles of the body are temporarily paralyzed during REM sleep (11), a phenomenon called atonia. Since most dreams occur during REM sleep, atonia prevents sleepers from acting out their dreams.

Dreaming

People spend around two hours dreaming every night. While the most vivid dreams usually occur during REM sleep, dreaming can happen during any sleep phase (12). Although some researchers propose that dreams play a role in learning and memory (13), scientists still aren’t completely sure why we dream.

How Much Sleep Do We Need?

The amount of sleep an individual needs varies from person to person. Recommended amounts of sleep also depend on a person’s age (14):

  • Babies: Newborns may sleep up to 18 hours per day , which is important for their growth and development. Infants and toddlers may sleep 11 to 16 hours a day, including nap times.
  • Children and Teens: From ages 3 to 18, children and teens need an average of about 9.5 hours of sleep per day, but healthy sleep times can range from 8 to 13 hours depending on age. Generally, children and teens need less sleep as they grow older.
  • Adults: Adults need between seven and nine hours of sleep each night.
  • Elderly People: As people age, their sleep may be shorter and involve waking up more often during the night. Despite these challenges, people over 65 still need seven to eight hours of sleep each night.

Many people understand the amount of sleep needed for optimal health, but still aren't getting enough sleep. Whether it’s because of longer hours at work or the temptation of social media and electronics, 30% of working American adults (15) receive less than six hours of sleep each night.

Optimizing Sleep

Understanding the science of sleep can help you recognize the importance of quality rest and take control of your sleep hygiene. Here are science-based tips for optimizing your sleep:

  • Allow Enough Time for Sleep: Getting enough sleep is necessary to reduce the body’s sleep drive and feel refreshed during the day. Many people won't sleep enough unless they intentionally carve out time for sleep. Find out how much sleep you need and make getting it a regular habit, even on the weekends.
  • Reduce Light Exposure Close to Bedtime: Light interferes with the body’s natural circadian rhythms and can make it more difficult to fall asleep. To reduce light exposure, turn off electronics at least an hour before bed and, if you work the night shift, be sure to use an eye mask or blackout curtains to eliminate light while sleeping.
  • Find Ways to Relax: Stress invokes the fight-or-flight response (16), which causes heart rate and blood pressure to increase. Being energized in this way is the opposite of what the body needs when falling asleep. Reduce stress at bedtime by finding ways to relax, like stretching, meditating, or reading a book.
  • Talk to a Doctor: Sleep is so crucial for health that anyone having issues sleeping should speak with their doctor. Doctors, sleep specialists, and counselors can address sleep issues and help you identify problems, so you can obtain quality rest.

There’s nothing quite like waking up refreshed after a good night’s rest. Your body and mind will thank you for making small changes to improve your sleep.


Sleep stages

It's not hard to prove that sleep is important. Rats totally deprived of sleep die within two or three weeks, according to research by the pioneering University of Chicago sleep scientist Allan Rechtschaffen. No one has done similar experiments on humans, for obvious reasons, but a 2014 study published in The Journal of Neuroscience found that a mere 24 hours of sleep deprivation caused healthy people to have hallucinations and other schizophrenia-like symptoms.

One reason it is difficult to get a handle on why we sleep is that sleep is actually pretty difficult to isolate and study. Sleep-deprivation studies are the most common way to study sleep, said Marcos Frank, a neuroscientist at the University of Washington, but depriving an animal of sleep disrupts many of its biological systems. It's hard to tell which outcomes are directly attributable to sleep deprivation rather than, say, stress.

Another reason sleep is hard to understand is that the brain may be doing two different things during the two major stages of sleep. As the night wears on, sleepers cycle through non-rapid eye movement (non-REM) and rapid-eye-movement (REM) sleep. Non-REM sleep is marked by slow brain waves called theta and delta waves. In contrast, the brain's electrical activity during REM sleep looks much like it does when a person is awake, but the muscles of the body are paralyzed. (If you've ever experienced sleep paralysis, it's because you woke from REM sleep before this paralysis ended.)

Studies have found differences in the biology of the brain during these different stages. For example, during non-REM sleep, the body releases growth hormone, according to a 2006 review of the biology of sleep published by Frank in the journal Reviews in the Neurosciences. Also during non-REM sleep, the synthesis of some brain proteins increases, and some genes involved in protein synthesis become more active, the review found. During REM sleep, in contrast, there does not appear to be any increase in this sort of protein-producing activity.


Why teenagers really do need an extra hour in bed

“MAKING teens start school in the morning is ‘cruel’, brain doctor claims.” So declared a British newspaper headline in 2007 after a talk I gave at an academic conference. One disbelieving reader responded&colon “This man sounds brain-dead.”

That was a typical reaction to work I was reporting at the time on teenage sleep patterns and their effect on performance at school. Six years on there is growing acceptance that the structure of the academic day needs to take account of adolescent sleep patterns. The latest school to adopt a later start time is the UCL Academy in London others are considering following suit.

So what are the facts about teenage slumber, and how should society adjust to these needs?

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The biology of human sleep timing, like that of other mammals, changes as we age. This has been shown in many studies. As puberty begins, bedtimes and waking times get later. This trend continues until 19.5 years in women and 21 in men. Then it reverses. At 55 we wake at about the time we woke prior to puberty. On average this is two hours earlier than adolescents. This means that for a teenager, a 7 am alarm call is the equivalent of a 5 am start for a person in their 50s.

“For a teenager, a 7 am alarm call is the equivalent of a 5 am start for a person in their 50s”

Precisely why this is so is unclear but the shifts correlate with hormonal changes at puberty and the decline in those hormones as we age.

However, biology is only part of the problem. Additional factors include a more relaxed attitude to bedtimes by parents, a general disregard for the importance of sleep, and access to TVs, DVDs, PCs, gaming devices, cellphones and so on, all of which promote alertness and eat into time available for sleep.

The amount of sleep teenagers get varies between countries, geographic region and social class, but all studies show they are going to bed later and not getting as much sleep as they need because of early school starts.

Mary Carskadon at Brown University in Providence, Rhode Island, who is a pioneer in the area of adolescent sleep, has shown that teenagers need about 9 hours a night to maintain full alertness and academic performance. My own recent observations at a UK school in Liverpool suggested many were getting just 5 hours on a school night. Unsurprisingly, teachers reported students dozing in class.

Evidence that sleep is important is overwhelming. Elegant research has demonstrated its critical role in memory consolidation and our ability to generate innovative solutions to complex problems. Sleep disruption increases the level of the stress hormone cortisol. Impulsive behaviours, lack of empathy, sense of humour and mood are similarly affected.

All in all, a tired adolescent is a grumpy, moody, insensitive, angry and stressed one. Perhaps less obviously, sleep loss is associated with metabolic changes. Research has shown that blood-glucose regulation was greatly impaired in young men who slept only 4 hours on six consecutive nights, with their insulin levels comparable to the early stages of diabetes.

Similar studies have shown higher levels of the hormone ghrelin, which promotes hunger, and lower levels of leptin, which creates a sense of feeling full. The suggestion is that long-term sleep deprivation might be an important factor in predisposing people to conditions such as diabetes, obesity and hypertension.

Adolescents are increasingly using stimulants to compensate for sleep loss, and caffeinated and/or sugary drinks are the usual choice. The half-life of caffeine is 5 to 9 hours. So a caffeinated drink late in the day delays sleep at night. Tiredness also increases the likelihood of taking up smoking.

Collectively, a day of caffeine and nicotine consumption, the biological tendency for delayed sleep and the increased alertness promoted by computer or cellphone use generates what Carskadon calls a “perfect storm” for delayed sleep in teenagers.

In the US, the observation that teenagers have biologically delayed sleep patterns compared to adults prompted several schools to put back the start of the school day. An analysis of the impact by Kyla Wahlstrom at the University of Minnesota found that academic performance was enhanced, as was attendance. Sleeping in class declined, as did self-reported depression.

In the UK, Monkseaton High School near Newcastle instituted a 10 am start in 2009 and saw an uptick in academic performance.

However, a later start by itself is not enough. Society in general, and teenagers in particular, must start to take sleep seriously.

Sleep is not a luxury or an indulgence but a fundamental biological need, enhancing creativity, productivity, mood and the ability to interact with others.

If you are dependent upon an alarm clock, or parent, to get you out of bed if you take a long time to wake up if you feel sleepy and irritable during the day if your behaviour is overly impulsive, it means you are probably not getting enough sleep. Take control. Ensure the bedroom is a place that promotes sleep – dark and not too warm – don’t text, use a computer or watch TV for at least half an hour before trying to sleep and avoid bright lights. Try not to nap during the day, and seek out natural light in the morning to adjust the body clock and sleep patterns to an earlier time. Avoid caffeinated drinks after lunch.

It is my strongly held view, based upon the evidence, that the efforts of dedicated teachers and the money spent on school facilities will have a greater impact and education will be more rewarding when, collectively, teenagers, parents, teachers and school governors start to take sleep seriously. In the universal language of school reports&colon we must do better.


Research Shows

Your Genes Affect Your Sleep Clock

Johns Hopkins sleep expert and neurologist Mark Wu, M.D., Ph.D., and fellow researchers recently identified a gene involved in the circadian regulation of sleep timing. When researchers removed this gene&mdashcalled &ldquowide awake&rdquo&mdashfrom fruit flies, the flies experienced problems falling asleep and staying asleep. A similar sleep gene exists in both humans and mice. Scientists continue to study this gene in hopes of understanding more about how processes within our cells affect our ability to sleep.

Your Body&rsquos Built-In Sleep Controls

According to Wu, there are two main processes that regulate sleep: circadian rhythms and sleep drive.

Circadian rhythms are controlled by a biological clock located in the brain. One key function of this clock is responding to light cues, ramping up production of the hormone melatonin at night, then switching it off when it senses light. People with total blindness often have trouble sleeping because they are unable to detect and respond to these light cues.

Sleep drive also plays a key role: Your body craves sleep, much like it hungers for food. Throughout the day, your desire for sleep builds, and when it reaches a certain point, you need to sleep. A major difference between sleep and hunger: Your body can&rsquot force you to eat when you&rsquore hungry, but when you&rsquore tired, it can put you to sleep, even if you&rsquore in a meeting or behind the wheel of a car. When you&rsquore exhausted, your body is even able to engage in microsleep episodes of one or two seconds while your eyes are open. Napping for more than 30 minutes later in the day can throw off your night&rsquos sleep by decreasing your body&rsquos sleep drive.

Why You Need Sleep

If you have ever felt foggy after a poor night&rsquos sleep, it won&rsquot surprise you that sleep significantly impacts brain function. First, a healthy amount of sleep is vital for &ldquobrain plasticity,&rdquo or the brain&rsquos ability to adapt to input. If we sleep too little, we become unable to process what we&rsquove learned during the day and we have more trouble remembering it in the future. Researchers also believe that sleep may promote the removal of waste products from brain cells&mdashsomething that seems to occur less efficiently when the brain is awake.

Sleep is vital to the rest of the body too. When people don&rsquot get enough sleep, their health risks rise. Symptoms of depression, seizures, high blood pressure and migraines worsen. Immunity is compromised, increasing the likelihood of illness and infection. Sleep also plays a role in metabolism: Even one night of missed sleep can create a prediabetic state in an otherwise healthy person. &ldquoThere are many important connections between health and sleep,&rdquo says Wu.


The case for self-control

Bedtime procrastination hadn’t received much attention before the 2014 research, says Floor Kroese, a health psychologist at Utrecht University in the Netherlands. “We knew that a lack of sleep was bad for people, but it was mostly studied in the context of sleeping problems.”

To find out how prevalent bedtime procrastination is, Kroese and her colleagues surveyed more than 2,400 people in the Netherlands. They found that about 53 percent of the respondents claimed that they went to bed later than they wanted at least twice a week. They also discovered that people who admit to regularly putting off bedtime were also more likely than others to report being poorly rested, be procrastinators in other areas of their lives, and score lower in self-control.

A key element of bedtime procrastination is that you don’t have a particular reason for not turning in. So staying up late because your kid was sick or you needed to pick up your friend from the airport doesn’t count. “That wouldn’t be bedtime procrastination, because then you simply couldn’t have gone to bed earlier,” Kroese says.

With bedtime procrastination, you could crawl into bed at any time. Your own better judgment is telling you to do so. So what’s stopping you? People tend to look upon sleeping as one of their favorite activities, so it’s probably not snoozing itself that’s the problem, Kroese’s colleagues have speculated.

Being unwilling to cut your relaxing evening activities short no doubt plays a role. But there’s also the matter of dragging yourself off the couch and tackling the final set of chores that stand between you and your pillow. Walking the dog or going upstairs to wash up “may sometimes seem like an almost insurmountable hurdle,” the researchers acknowledged. Moving these chores to earlier in the evening might be one way to sidestep bedtime procrastination, they proposed. That could mean popping your contact lenses out when you get home from work or brushing your teeth right after dinner (or at least right after your final evening snack).

The team has also found that people who have to resist more temptations throughout the day are more likely to cave to bedtime procrastination come evening, when their self-control is at its nadir. “There may be evenings on which it is a bad idea to start watching a favorite TV series close to bedtime, and there may be evenings on which it is no problem at all,” they recently wrote in Frontiers in Psychology. If there were a way to track how many times you’ve had to battle your impulses to watch YouTube videos at work or eat chocolate pie for lunch, it might be easier to predict when you’re most susceptible to bedtime procrastination, they said.


How Can You Have a Healthier Sleep Cycle?

While you don’t have full control of your sleep cycle, you can take steps to improve your chances of having a healthy progression through each sleep stage.

A key step is to focus on improving your sleep hygiene, which refers to your sleep environment (mattress, pillow, sheets, etc.) and sleep-related habits. Achieving a more consistent sleep schedule, getting natural daylight exposure, avoiding alcohol before bedtime, and eliminating noise and light disruptions can help you get uninterrupted sleep and promote proper alignment of your circadian rhythm.

If you find that you have excessive daytime sleepiness or otherwise suspect that you might have a sleep disorder like sleep apnea, it’s important to talk with a doctor who can most appropriately guide your care. Addressing underlying issues may pave the way for more complete and restorative sleep cycles.


How we sleep today may forecast when Alzheimer’s disease begins

What would you do if you knew how long you had until Alzheimer’s disease set in? Don’t despair. New UC Berkeley research suggests one defense against this virulent form of dementia — for which no treatment currently exists — is deep, restorative sleep, and plenty of it.

Neuroscientists Matthew Walker and Joseph Winer have found a way to estimate, with some degree of accuracy, a time frame for when Alzheimer’s is most likely to strike in a person’s lifetime.

“We have found that the sleep you’re having right now is almost like a crystal ball telling you when and how fast Alzheimer’s pathology will develop in your brain,” said Walker, a UC Berkeley professor of psychology and neuroscience and senior author of the paper published today, Sept. 3, in the journal Current Biology.

“The silver lining here is that there’s something we can do about it,” he added. “The brain washes itself during deep sleep, and so there may be the chance to turn back the clock by getting more sleep earlier in life.”

Walker and fellow researchers matched the overnight sleep quality of 32 healthy older adults against the buildup in their brains of the toxic plaque known as beta-amyloid, a key player in the onset and progression of Alzheimer’s, which destroys memory pathways and other brain functions and afflicts more than 40 million people worldwide.

Their findings show that the study participants who started out experiencing more fragmented sleep and less non-rapid eye movement (non-REM) slow-wave sleep were most likely to show an increase in beta-amyloid over the course of the study.

Although all participants remained healthy throughout the study period, the trajectory of their beta-amyloid growth correlated with baseline sleep quality. The researchers were able to forecast the increase in beta-amyloid plaques, which are thought to mark the beginning of Alzheimer’s.

A wake-up call

“Rather than waiting for someone to develop dementia many years down the road, we are able to assess how sleep quality predicts changes in beta-amyloid plaques across multiple timepoints. In doing so, we can measure how quickly this toxic protein accumulates in the brain over time, which can indicate the beginning of Alzheimer’s disease,” said Winer, the study’s lead author and a Ph.D. student in Walker’s Center for Human Sleep Science at UC Berkeley.

In addition to predicting the time it is likely to take for the onset of Alzheimer’s, the results reinforce the link between poor sleep and the disease, which is particularly critical in the face of a tsunami of aging baby boomers on the horizon.

While previous studies have found that sleep cleanses the brain of beta-amyloid deposits, these new findings identify deep non-REM slow-wave sleep as the target of intervention against cognitive decline.

And though genetic testing can predict one’s inherent susceptibility to Alzheimer’s, and blood tests offer a diagnostic tool, neither offers the potential for a lifestyle therapeutic intervention that sleep does, the researchers point out.

“If deep, restorative sleep can slow down this disease, we should be making it a major priority,” Winer said. “And if physicians know about this connection, they can ask their older patients about their sleep quality and suggest sleep as a prevention strategy.”

How they conducted the study

The 32 healthy participants in their 60s, 70s and 80s who are enrolled in the sleep study are part of the Berkeley Aging Cohort Study headed by UC Berkeley public health professor William Jagust, also a co-author on this latest study. The study of healthy aging was launched in 2005 with a grant from the National Institutes of Health.

For the experiment, each participant spent an eight-hour night of sleep in Walker’s lab while undergoing polysomnography, a battery of tests that record brain waves, heart rate, blood-oxygen levels and other physiological measures of sleep quality.

Over the course of the multi-year study, the researchers periodically tracked the growth rate of the beta-amyloid protein in the participants’ brains using positron emission tomography, or PET scans, and compared the individuals’ beta-amyloid levels to their sleep profiles.

Researchers focused on the brain activity present during deep slow-wave sleep. They also assessed the study participants’ sleep efficiency, which is defined as actual time spent asleep, as opposed to lying sleepless in bed.

The results supported their hypothesis that sleep quality is a biomarker and predictor of disease down the road.

Traveling into the future

“We know there’s a connection between people’s sleep quality and what’s going on in the brain, in terms of Alzheimer’s disease. But what hasn’t been tested before is whether your sleep right now predicts what’s going to happen to you years later,” Winer said. “And that’s the question we had.”

And they got their answer: “Measuring sleep effectively helps us travel into the future and estimate where your amyloid buildup will be,” Walker said.

As for next steps, Walker and Winer are looking at how they can take the study participants who are at high risk of contracting Alzheimer’s and implement methods that might boost the quality of their sleep.

“Our hope is that if we intervene, then in three or four years the buildup is no longer where we thought it would be because we improved their sleep,” Winer said.

“Indeed, if we can bend the arrow of Alzheimer’s risk downward by improving sleep, it would be a significant and hopeful advance,” Walker concluded.

In addition to Walker, Winer and Jagust, co-authors of the study are Bryce Mander at UC Irvine, Samika Kumar and Mark Reed at UC Berkeley, and Suzanne Baker at the Lawrence Berkeley National Laboratory.


Why Do My Eyes Close When I Sneeze?

Is it a foregone conclusion that we can't help closing our eyes during a sneeze? Not quite, researchers say.

It is possible (albeit difficult) to keep our eyes open during a sneeze, said Dr. David Huston, an associate dean at the Texas A&M College of Medicine Houston campus and an allergist at Houston Methodist Hospital.

"The fact that it is possible to sneeze with the eyes open suggests that it is not hardwired or mandatory," Huston said in a statement. It's not entirely clear why people blink while sneezing, but it likely plays a protective role, he said. [Why Do People Sneeze in Threes?]

Sneezing, known to researchers as the sternutation reflex, protects our nasal passageways from foreign particles by forcing a 10-mph whoosh of air from the lungs. (Previous accounts put that speed at 100 mph, but a 2013 study published in the journal PLOS ONE found that six volunteers had sneeze speeds of 4.5 meters per second, or 10 mph).

However, sneezing involves more than expelling air and foreign particles. When stimulated, the brain stem's sneeze center orders muscle contractions from esophagus to sphincter. That includes the muscles controlling the eyelids. Some sneezers even shed a few tears.

Perhaps people close their eyes while sneezing to prevent the expelled particles from entering their eyes, Huston said.

"By automatically shutting the eyelids when a sneeze occurs, more irritants can potentially be prevented from entering and aggravating the eyes," Huston said.

If they're so inclined, people can try to keep their eyes open during a sneeze. Moreover, they don't have to worry about their eyeballs popping out, a tall tale that has no scientific merit, he said. This allegedly happened in 1882, according to a New York Times article about a woman who was said to have dislocated an eyeball (known as subluxation in the medical world) after a fit of severe sneezing.

"There is little to no evidence to substantiate such claims," Huston said. "Pressure released from a sneeze is extremely unlikely to cause an eyeball to pop out, even if your eyes are open."

Rather, increased pressure from a violent sneeze can build in the blood vessels, not in the eyes or the muscles surrounding them. This increased vascular pressure can lead to ruptured capillaries (small blood vessels), which, once broken, are often visible in the eyeballs or on a person's face.

"For example, during childbirth, excessive straining can cause some veins to hemorrhage, leaving a mother's eyes or face to appear red or markedly bruised," Huston said, "but it is irresponsible to claim that such pressure could dislodge the eye from its socket."


When You Can’t Sleep, How Good Is Lying in Bed With Your Eyes Closed?

Reddit is a great forum for raising scientific questions, but the fact that it’s discussion-based makes it difficult to know when a debate has settled on the best answer, objectively speaking. Exhibit A concerns the value of lying down with your eyes closed. How much does it do for you compared to actual sleep? The whole exercise can seem like a waste. Is it?

Part of what makes this question so slippery is that it hinges in large part on the matter of what sleep is actually for. We can all name the benefits of sleep, but saying what sleep accomplishes is a far cry from identifying what sleep is meant to do. The distinction is important. If the point of sleep is that being inactive frees up our energy for other tasks (say, recovering from a cold), we might expect lying in bed with our eyes closed—what some studies call “quiet wakefulness”—to accomplish much the same thing.

Researchers are growing increasingly confident, though, that sleep evolved specifically to recharge the brain. Dr. Chiara Cirelli, a neuroscientist at the University of Wisconsin, has been studying the difference between sleep and quiet wake in humans. She says that while we’re awake, all of our neurons are constantly firing, but that when we’re asleep, the neurons revert to an “up-and-down” state in which only some are active at a given time. During some stages of sleep, all neuron activity goes silent. And that’s likely when the restful part of sleep takes place.

“This period of silence and hyperpolarization of the cell membrane is probably related to the restorative function of sleep,” Cirelli told me. “The fact that there are these periods of total silence, that’s very typical and unique of sleep relative to wake and there might be something related to that.”

To understand the value of total neural silence, let’s look at another kind of sleeping animal—dolphins. Dolphins, along with whales, some sharks, and a variety of other underwater critters, need to stay moving to breathe. It follows that these animals can’t go completely unconscious like humans can—otherwise, the dolphins couldn’t come up for air, and oxygenated water would stop flowing over the sharks’ gills. And the research seems to bear that out: Brain scans show that dolphins never go into a full sleep state instead, they turn off half of their brain for about eight hours a day, leaving the other half alert. This kind of rest has come to be called “unihemispheric sleeping.”

The closest humans ever get to unihemispheric sleep is when a person who’s extremely sleep-deprived shows signs of what Cirelli calls “local sleep in wake,” in which a few neurons turn off by themselves. The effect is unnoticeable from the outside, because the sleep-deprived subject is still awake and moving, but researchers are able to record the changes using deep-scanning technology that measures individual neurons.

But it’s not until we get access to real, deep sleep that we get a cognitive boost from rest. In other studies, test subjects who were made to identify letters flashed on a screen for several hundred milliseconds at a time generally did worse at the exam over the course of a day. Those who got to take a nap halfway through showed more cognitive recovery than those who simply rested quietly, suggesting that there’s a unique benefit to sleep that you don’t get with quiet wakefulness, microsleep, or unihemispheric sleep.


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