Chapter 10. Biological Rhythms and Sleep
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By Dwayne Godwin and Jorge Cham ABOUT THE AUTHOR(S) Dwayne Godwin is a neuroscientist at the Wake Forest University School of Medicine. Jorge Cham draws the comic strip Piled Higher and Deeper at www.phdcomics.com. © 2014 Scientific American
Link ID: 19473 - Posted: 04.12.2014
by Meghan Rosen Shaking off jet lag could be as easy as downloading an app. Researchers developed the iPhone app, called Entrain, using mathematical analyses of humans’ daily rhythms to calculate the quickest way to adjust to new time zones. Users plug in their destination and arrival time, and Entrain advises times of the day to soak up or stay out of the light. The schedules are surprisingly simple, says mathematical biologist Daniel Forger, of the University of Michigan in Ann Arbor. “They might say, ‘Hey you should keep the lights on in your room until midnight,’” he says. “Or ‘you should stay in darkness until 10 a.m.’” Scientists have previously created mathematical equations that describe how humans’ internal clocks respond to light, Forger says. He and a colleague used a computer program to solve the tricky problem of finding the best lighting schedules for more than 1,000 possible trips. To do so, the researchers asked a question: If a traveler wants to move their body’s clock from New York to London time, for instance, what lighting schedule gets them there fastest? The pair reports the results April 10 in PLOS Computational Biology. K. Serkh and D.B. Forger. Optimal schedules of light exposure for rapidly correcting circadian misalignment. PLOS Computational Biology. Vol.10, April 10, 2014, p. e1003525. Doi: 10.1371/journal.pcbi.1003523. © Society for Science & the Public 2000 - 2013.
Keyword: Biological Rhythms
Link ID: 19472 - Posted: 04.12.2014
By JoNel Aleccia The engineer who drove a speeding commuter train off the rails in New York last year may have suffered from the most severe form of a dangerous sleep disorder, but health experts say he has plenty of company. As many as 22 million people in the U.S. — or up to 7 percent of the population — may suffer from obstructive sleep apnea, experts say. It’s a condition that causes airways to collapse during sleep, cutting off breathing dozens or sometimes hundreds of times a night, leaving them bleary-eyed and drowsy, even after a full night’s rest. William Rockefeller, 46, was diagnosed after the December 2013 crash that killed four and injured more than 70 with severe obstructive sleep apnea, documents released this week show. On a scale where as few as five sleep disruptions an hour can make someone sleepy, and 30 episodes are considered severe, Rockefeller logged about 66 arousals an hour, doctors said. “His sleep was really fragmented,” said Dr. Phyllis Zee, a sleep expert with the Northwestern Medicine Sleep and Circadian Rhythms Research Program. “Even if he were to sleep seven or eight hours, he would be sleep-deprived.” Zee and her colleagues suspected that Rockefeller might suffer from sleep deprivation. He was obese, records show, and there’s a certain fatigued look that she saw in news photos of the engineer. “That was one of my thoughts, ‘Oh my goodness, he has (OSA),’” she said.
Link ID: 19457 - Posted: 04.08.2014
By Helen Briggs BBC News Sleep loss may be more serious than previously thought, causing a permanent loss of brain cells, research suggests. In mice, prolonged lack of sleep led to 25% of certain brain cells dying, according to a study in The Journal of Neuroscience. If the same is true in humans, it may be futile to try to catch up on missed sleep, say US scientists. They think it may one day be possible to develop a drug to protect the brain from the side-effects of lost sleep. The study, published in The Journal of Neuroscience, looked at lab mice that were kept awake to replicate the kind of sleep loss common in modern life, through night shifts or long hours in the office. A team at the University of Pennsylvania School of Medicine studied certain brain cells which are involved in keeping the brain alert. After several days of sleep patterns similar to those followed by night workers - three days of night shifts with only four to five hours sleep in 24 hours - the mice lost 25% of the brain cells, known as locus coeruleus (LC) neurons. The researchers say this is the first evidence that sleep loss can lead to a loss of brain cells. But they add that more work needs to be done to find out if people who miss out on sleep might also be at risk of permanent damage. Prof Sigrid Veasey of the Center for Sleep and Circadian Neurobiology, told BBC News: "We now have evidence that sleep loss can lead to irreversible injury. "This might be in a simple animal but this suggests to us that we are going to have to look very carefully in humans." BBC © 2014
Link ID: 19382 - Posted: 03.19.2014
By Christina Ianzito, We get it: Sleep is good for us. The National Sleep Foundation regularly campaigns “to celebrate the health benefits of sleep,” and experts have been boosting sleep’s values as no less important than proper diet and exercise. Insufficient sleep has been linked to stroke, obesity and heart disease. But sleeping too much may also be risky: It, too, is associated with a higher risk of heart disease and obesity, not to mention diabetes and depression. So, how much is too much? And if you’re sleep-deprived during the week, does sleeping 10 or 11 hours on Saturday and Sunday to catch up put you in any jeopardy? Most experts say that a healthy amount of sleep for an adult is a regular seven to nine hours a night. And the operative term here is “regular,” meaning the issue isn’t the college kid who power-sleeps 15 hours on vacation to catch up from too much studying (or partying). When scientists refer to “long sleepers,” they’re referring to people who consistently sleep nine or more hours a night, says Kristen Knutson, a biomedical anthropologist who focuses on sleep research at the University of Chicago’s Department of Medicine. “If you’ve been pulling all-nighters, by all means extend your sleep on the weekend if you can; try to catch up,” Knutson says, “but if you’re sleeping nine or 10 hours night after night after night for months on end . . . then we’ve got to understand why are you sleeping so much.” You might be getting poor-quality sleep, she adds, or are “already on the pathway to illness and your body is reacting by wanting you to sleep more.” © 1996-2014 The Washington Post
Link ID: 19369 - Posted: 03.17.2014
By JAN HOFFMAN COLUMBIA, Mo. – Jilly Dos Santos really did try to get to school on time. She set three successive alarms on her phone. Skipped breakfast. Hastily applied makeup while her fuming father drove. But last year she rarely made it into the frantic scrum at the doors of Rock Bridge High School here by the first bell, at 7:50 a.m. Then she heard that the school board was about to make the day start even earlier, at 7:20 a.m. “I thought, if that happens, I will die,” recalled Jilly, 17. “I will drop out of school!” That was when the sleep-deprived teenager turned into a sleep activist. She was determined to convince the board of a truth she knew in the core of her tired, lanky body: Teenagers are developmentally driven to be late to bed, late to rise. Could the board realign the first bell with that biological reality? The sputtering, nearly 20-year movement to start high schools later has recently gained momentum in communities like this one, as hundreds of schools in dozens of districts across the country have bowed to the accumulating research on the adolescent body clock. In just the last two years, high schools in Long Beach, Calif.; Stillwater, Okla.; Decatur, Ga.;, and Glens Falls, N.Y., have pushed back their first bells, joining early adopters in Connecticut, North Carolina, Kentucky and Minnesota. The Seattle school board will vote this month on whether to pursue the issue. The superintendent of Montgomery County, Md., supports the shift, and the school board for Fairfax County, Va., is working with consultants to develop options for starts after 8 a.m. © 2014 The New York Times Company
By Pippa Stephens Health reporter, BBC News People are less likely to yawn when others do as they get older, a study has found. Contagious yawning is linked more closely to a person's age than their ability to empathise, as previously thought, US-based scientists said. It also showed a stronger link to age than tiredness or energy levels. Researchers are now looking at whether the ability to catch yawns from other people is inherited, with the hope of helping treat mental health disorders. Autism and schizophrenia sufferers are reportedly less able to catch yawns, researchers said, so understanding the genes that might code for contagious yawning could illuminate new pathways for treatment. In the study, published in the journal Plos One, 328 participants were shown a three-minute video showing other people yawning. Each subject had to click a button every time they yawned. Levels of tiredness Overall, 68% of the participants yawned. Of those, 82% of people aged under 25 yawned, compared with 60% of people aged between 25 and 49, and 41% of people aged over 50. Dr Elizabeth Cirulli, assistant professor of medicine at Duke University in Durham, North Carolina, led the study. She said: "This is the first study to look at a whole bunch of factors. It is the largest study, in terms of the number of people involved, to date." Dr Cirulli said she did not know why contagious yawning decreased with age. BBC © 2014
by Kat Arney Feeling dopey? Refresh your "circadian eye" with a burst of orange light. Light is a powerful wake-up call, enhancing alertness and activity. Its effect is controlled by a group of photoreceptor cells in the eyeball that make the light-sensing pigment melanopsin. These cells, which work separately to the rods and cones needed for vision, are thought to help reset animals' body clocks - or circadian rhythms. Studies with people who are blind suggest this also happens in humans, although the evidence isn't conclusive. To find out how melanopsin wakes up the brain, Gilles Vandewalle at the University of Liege, Belgium, and his team gave 16 people a 10-minute blast of blue or orange light while they performed a memory test in an fMRI scanner. They were then blindfolded for 70 minutes, before being retested under a green light. People initially exposed to orange light had greater brain activity in several regions related to alertness and cognition when they were retested, compared with those pre-exposed to blue light. Light switch Vandewalle thinks that melanopsin is acting as a kind of switch, sending different signals to the brain depending on its state. Orange light, which has the longer wavelength, is known to make the pigment more light-sensitive, but blue light has the opposite effect. Green light lies somewhere in the middle. The findings suggest that pre-exposure to orange light pushes the balance towards the more light-sensitive form of melanopsin, enhancing the response in the brain. © Copyright Reed Business Information Ltd.
by Nathan Seppa MS patients who harbor low levels of vitamin D early in their disease fare worse over the next several years than patients with higher levels. Multiple sclerosis is marked by damage to the fatty sheaths coating nerve fibers in the brain. The result can be an off-and-on series of symptoms including loss of muscle control, numbness and problems thinking. Vitamin D, which the body makes from sun exposure, has shown promise in fighting a variety of diseases and may limit this MS onslaught (SN: 7/16/11, p. 22). In 2002, researchers studying the effect of the drug beta-interferon-1b against MS set aside blood samples from 465 patients. When researchers recently analyzed those samples, they found that patients who had blood levels of vitamin D exceeding 20 nanograms per milliliter at six and 12 months after the onset of MS had fewer symptom flare-ups during the rest of the five-year study than those with lower readings did. Some scientists think 20 nanograms per milliliter is a healthy level; others see 30 as a healthier minimum. MRI scans revealed that, after five years, those who had started out with low vitamin D levels had four times as much myelin damage as those who had higher levels. The results appear in the March JAMA Neurology. A. Ascherio et al. Vitamin D as an early predictor of multiple sclerosis activity and progression. JAMA Neurology. Vol. 71, March 2014, p. 306. doi:10.1001/jamaneurol.2013.5993. © Society for Science & the Public 2000 - 2013
Linda Carroll TODAY contributor Insomnia isn’t something that just happens at night. Researchers have now shown that insomniacs have more active brains than sound sleepers, according to a report published Friday in the journal Sleep. That means sleeplessness may, in fact, have its roots in brain wiring that affects the way our minds work, no matter what time of day it is. “We see insomnia now as more of a 24/7 disorder,” said Dr. Rachel Salas, an assistant professor of neurology at the Johns Hopkins University School of Medicine and lead author of the new study. “It’s like a light switch is continually on. So their brains are always running.” Salas originally thought that sound sleepers would be the ones with more alert and plastic brains. (Brain plasticity basically means how neural pathways can be modified by experience or that it is able to adapt or grow.) To prove the theory, Salas set up an experiment that compared 18 chronic insomniacs to 10 sound sleepers. All of the study volunteers were hooked up to a device that sends magnetic waves through the skull and into the brain. Because transcranial magnetic stimulation (TMS) can be aimed a specific site, the researchers were able to target a point in the motor cortex that controls movements of the thumb. Each magnetic pulse sparked an involuntary twitching of the digit. After 65 run-throughs with the TMS, study volunteers were asked to practice moving their thumbs on their own in a manner opposite to the one that was sparked by the TMS. So, for example, if the TMS sent volunteers’ thumbs flicking up and left, they would be asked to wiggle their digits down and right.
Link ID: 19305 - Posted: 03.01.2014
By Meeri Kim, How often, and how well, do you remember your dreams? Some people seem to be super-dreamers, able to recall effortlessly their dreams in vivid detail almost every day. Others struggle to remember even a vague fragment or two. A new study has discovered that heightened blood flow activity within certain regions of the brain could help explain the great dreamer divide. In general, dream recall is thought to require some amount of wakefulness during the night for the vision to be encoded in longer-term memory. But it is not known what causes some people to wake up more than others. A team of French researchers looked at brain activation maps of sleeping subjects and homed in on areas that could be responsible for nighttime wakefulness. When comparing two groups of dreamers on the opposite ends of the recall spectrum, the maps revealed that the temporoparietal junction — an area responsible for collecting and processing information from the external world — was more highly activated in high-recallers. The researchers speculate that this allows these people to sense environmental noises in the night and wake up momentarily — and, in the process, store dream memories for later recall. In support of this hypothesis, previous medical cases have found that when these same portions of the brain are damaged by stroke, patients lose the ability to remember their dreams, even though they can still achieve the REM (rapid eye movement) stage of sleep in which dreaming usually occurs. © 1996-2014 The Washington Post
If you ever feel like your emotions are getting the best of you, you may want to try dimming the lights. According to researchers at the University of Toronto Scarborough, bright light can make us more emotional — for better or for worse — making us experience both positive and negative feelings more intensely. The findings seem to contradict commonly held notions that people feel happier and more optimistic on bright, sunny days and gloomier on dark, cloudy days. In fact, the idea for the study was spurred by findings that suicide rates peak in the late spring and summer, when sunshine is most abundant. “I was very surprised by this,” study author Alison Jing Xu told CBC News. Xu is an assistant professor of management at UTSC and the Rotman School of Management. “Normally I would say if brighter days generally increase people’s affect, then suicide rates should peak in winter — but actually it does not,” she said. Xu, along with the study’s co-author Aparna Labroo of Northwestern University in the U.S., conducted six experiments to explore the relationship between light and emotion. Their paper is published in the Journal of Consumer Psychology. Participants in each case were divided into two groups: Some were placed in a brightly lit room where fluorescent ceiling lights were turned on, while others were placed in a dimly lit room where the only light came from computer monitors. © CBC 2014
By ANAHAD O'CONNOR Many people occasionally wake up in the middle of the night and find themselves unable to get back to sleep. But if it happens often, and you are consistently tired and not functioning well during the day, that is indicative of a problem, said Dr. Meir H. Kryger, a professor at Yale School of Medicine and the author of “The iGuide to Sleep.” Stressful events, a loud pet or a snoring bedmate may be to blame, or the problem could be a medical issue such as a cough, sleep apnea or getting up to urinate — which could be a sign of diabetes. Dr. Kryger said he has had patients who are stirred awake by the sensation of their heart beating rapidly because of a cardiac rhythm problem. Worrying about being awake only makes the problem worse. “We see that in patients who’ve had insomnia for a while,” Dr. Kryger said. “They wake up and become so angry, frustrated and aroused that they can’t fall asleep.” In some cases better habits can help. Nicotine or alcohol levels fall during sleep and can cause people to awaken, so quitting smoking or avoiding alcoholic beverages, especially before bedtime, can help. Steer clear of heavy or spicy meals before trying to sleep if heartburn or acid reflux is keeping you up. You may be tempted to nap during the day to compensate for lost sleep time, but this can just prolong the problem, Dr. Kryger said. Avoid taking naps that are longer than 20 minutes, particularly in the evening. If you wake up at night and find that you still cannot get back to asleep after 20 minutes, do not lie there in anguish staring at your clock. Get out of bed and do something that distracts and relaxes you, like reading a book. Then return to bed when you feel sleepy. © 2014 The New York Times Company
Link ID: 19276 - Posted: 02.22.2014
By Caitlin Kirkwood Glorious, refreshing sleep is eluding the majority of Americans. According to the National Sleep Foundation’s 2013 International Bedroom Poll 56 percent of people between the ages of 25 and 55 get an insufficient amount of sleep on workdays. On non-workdays individuals are then more likely to oversleep. They spend an additional 45 minutes catching Z’s in an attempt to compensate for accrued workweek sleep debt. Why are we constantly playing sleep-catch up during free time? As a society we are socially jet lagged. Social jet lag is the difference betweensleep patterns on work days and free days. These inconsistent sleeping habits result in sleep loss that is reminiscent of flying west across several time zones every Friday evening and traveling back East come Monday morning. The pattern reveals a critical disparity between society-imposed obligations, like work and family commitments, and our innate biological clock. Social jet lag might not sound like a big deal. What’s an hour or two of sleep lost here and there? But the chronic misalignment between our social and biological clocks is wreaking havoc on our health. Large-scale epidemiological studies have pointed a finger at short sleep duration for it’s causative role in the nationwide obesity crisis. When you get too little sleep, normal levels of appetite hormones are altered in a way that could lead to increased food consumption and weight gain. Unfortunately for people struggling with social jet lag, short sleep duration comes with the territory of the workweek. Some data even suggest that for every hour the biological clock is offset from the social clock, the chances of being overweight shoot-up by a whopping 33 percent. And supersizing the body mass index isn’t the only problem. Social jet lag has also been linked to the increased likelihood of nicotine and alcohol use, which independently contribute to additional health problems. © 2014 Scientific American
Link ID: 19240 - Posted: 02.12.2014
| by Nina Bahadur Addiction and eating disorder recovery site Rehabs.com worked with digital marketing agency Fractl on a project looking at the origins of Body Mass Index (BMI) measurements, and how the bodies of ideal women have compared to national averages over time. And their findings show that models and movie stars are getting smaller than the average American woman at unprecedented rates. Though BMI measurements don't distinguish between fat and muscle, and are thus fairly inaccurate in determining whether someone is obese or not, BMI data from the past makes for interesting comparisons. According to the Center for Disease Control, the BMI of the average American women has steadily increased over the past half a century, from 24.9 in 1960 to 26.5 in the present day. In a similar vein, Rehabs.com found that the difference between models' weights and the weight of the average American woman has grown from 8 percent in 1975 to over 23 percent today. The bottom line? There's more of a noticeable gap between the bodies of idealized women and everyday people. Picking up on this disparity, brands like Dove, Debenham's and H&M have made efforts to include diverse body types in their catalogs and ads. Organizations like The Representation Project are working to educate women and girls about media literacy and how to handle the sexualized images of women we see on television, billboards and the Internet. (Of course, we still have a very long way to go.) In addition to the work of brands and organizations, looking back on the "ideal" women throughout the past century tells us just how arbitrary any vision of "the perfect body" is. Sex symbols have varied in terms of body shape, height, weight and tone, from the hourglass figure of Mae West to the waif-like Kate Moss. Though the diversity of these icons is limited -- they are all white, and none could be accurately described as plus-size -- it's gratifying to see that different body types have been construed as sexy, and likely will be again. © 2014 TheHuffingtonPost.com, Inc
Keyword: Anorexia & Bulimia
Link ID: 19222 - Posted: 02.08.2014
Posted by Maria Konnikova On a typical workday morning, if you’re like most people, you don’t wake up naturally. Instead, the ring of an alarm clock probably jerks you out of sleep. Depending on when you went to bed, what day of the week it is, and how deeply you were sleeping, you may not understand where you are, or why there’s an infernal chiming sound. Then you throw out your arm and hit the snooze button, silencing the noise for at least a few moments. Just another couple of minutes, you think. Then maybe a few minutes more. It may seem like you’re giving yourself a few extra minutes to collect your thoughts. But what you’re actually doing is making the wake-up process more difficult and drawn out. If you manage to drift off again, you are likely plunging your brain back into the beginning of the sleep cycle, which is the worst point to be woken up—and the harder we feel it is for us to wake up, the worse we think we’ve slept. (Ian Parker wrote about the development of a new drug for insomnia in the magazine last week.) One of the consequences of waking up suddenly, and too early, is a phenomenon called sleep inertia. First given a name in 1976, sleep inertia refers to that period between waking and being fully awake when you feel groggy. The more abruptly you are awakened, the more severe the sleep inertia. While we may feel that we wake up quickly enough, transitioning easily between sleep mode and awake mode, the process is in reality far more gradual. Our brain-stem arousal systems (the parts of the brain responsible for basic physiological functioning) are activated almost instantly. But our cortical regions, especially the prefrontal cortex (the part of the brain involved in decision-making and self-control), take longer to come on board. © 2013 Condé Nast.
Link ID: 19211 - Posted: 02.06.2014
|By Roni Jacobson There is nothing like a good night's sleep to help you feel your best the next day. Now scientists are finding that good sleep habits may do more than restore cognitive function on a nightly basis—they may also fortify the brain over the long term, according to a new study in the Journal of Neuroscience. Researchers at the University of Wisconsin–Madison found that during sleep, activity ramps up in genes that are involved in producing oligodendrocytes—brain cells responsible for coating neurons with myelin. Myelin is the brain's insulating material. The fatty substance surrounds the signal-transmitting tail that extends from every neuron, enabling electrical communications to travel quickly and efficiently to other neurons. Myelin deficiency is at the root of the neurodegenerative disease multiple sclerosis and can contribute to symptoms such as fatigue, vision and hearing impairment, and a loss of coordination. In this study, sleeping mice had heightened activity in the genes responsible for creating oligodendrocytes, but awake or sleep-deprived rodents showed greater activity in genes involved in cellular stress and death. Chiara Cirelli, a neuroscientist and author on the paper, suggests that sleep helps cells regenerate and repair themselves, by enabling the body to produce new myelin after it has deteriorated. Cellular repair probably takes weeks or even months, however, so pulling an occasional all-nighter is unlikely to disrupt the process. © 2014 Scientific American
Link ID: 19185 - Posted: 01.30.2014
By James Gallagher Health and science reporter, BBC News Doing the night shift throws the body "into chaos" and could cause long-term damage, warn researchers. Shift work has been linked to higher rates of type 2 diabetes, heart attacks and cancer. Now scientists at the Sleep Research Centre in Surrey have uncovered the disruption shift work causes at the deepest molecular level. Experts said the scale, speed and severity of damage caused by being awake at night was a surprise. The human body has its own natural rhythm or body clock tuned to sleep at night and be active during the day. It has profound effects on the body, altering everything from hormones and body temperature to athletic ability, mood and brain function. The study, published in Proceedings of the National Academy of Sciences, followed 22 people as their body was shifted from a normal pattern to that of a night-shift worker. Blood tests showed that normally 6% of genes - the instructions contained in DNA - were precisely timed to be more or less active at specific times of the day. Once the volunteers were working through the night, that genetic fine-tuning was lost. "Over 97% of rhythmic genes become out of sync with mistimed sleep and this really explains why we feel so bad during jet lag, or if we have to work irregular shifts," said Dr Simon Archer, one of the researchers at the University of Surrey. BBC © 2014
By Megan Wiegand and Slate, Tips for beating the seasonal blues are as numerous as the winter night is long. Light boxes, touted to “uplift people’s spirits” and “improve mood and energy,” offer a New-Agey-seeming solution to propel us into the cold as if it’s the first beautiful day of spring. But can sitting in front of a light for a few minutes a day actually counteract the dreariest months? Yes, in many cases. Light-box therapy has been shown to alleviate symptoms in people who suffer from seasonal affective disorder, or SAD. Symptoms of this form of depression — they can include lost interest in beloved activities, overeating, loss of energy, disrupted sleep cycles and feelings of hopelessness or guilt — typically appear in late fall or early winter and dissipate in spring. Women are twice as likely as men to seek treatment for SAD, and those farther away from the equator are more likely to be diagnosed: About 11 percent of Mainers have a clinical SAD diagnosis, but only 2 percent of Floridians report the illness, according to Kathryn Roecklein, an assistant professor of psychology at the University of Pittsburgh. One tool doctors use to treat SAD is light-box therapy. Light boxes use bright white fluorescent bulbs (or sometimes blue light) that reproduce some wavelengths of the sun’s light. They contain filters to block harmful UV rays and come in various shapes, sizes, light types and price points. © 1996-2014 The Washington Post
By C. CLAIBORNE RAY Q. Why do I wake up at exactly the same time every night, without any stimulus? It has happened all my life, and it doesn’t even matter what time I went to bed. A. What you are experiencing is probably a normal period of relative alertness that happens in the middle of the night, said Dr. Carl W. Bazil, director of the division of epilepsy and sleep at NewYork-Presbyterian/Columbia University Medical Center. “Most people realize that there is a natural drowsiness midday, usually around lunchtime,” Dr. Bazil said. “This is why many fortunate cultures developed the siesta.” But the reverse normally happens at night. The two interludes are both part of the body’s circadian rhythm, which he said is “controlled by an internal clock but of course influenced by lots of external things,” like caffeine, light, exercise and stress. Dr. Bazil said it might also help those who wake up midsleep to know that “before the advent of electrical lighting, it was normal for people to go to bed at sundown, sleep for about four hours and arise during that natural alertness for a few hours before returning for a ‘second sleep.’ ” © 2014 The New York Times Company