Chapter 10. Biological Rhythms and Sleep
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by Bethany Brookshire Drugs that treat anxiety can be real downers. While they may help you feel less anxious, drugs such as Valium and Xanax can leave you drowsy and unfocused. Long-term use of these compounds, a class of drugs called the benzodiazepines, can lead to dependence and tolerance. And patients often need higher and higher doses to calm their anxiety. Getting off the drugs requires careful weaning to avoid insomnia, tremors and other nasty withdrawal effects. But Subhashis Banerjee and colleagues at the Scripps Research Institute in Jupiter, Fla., have identified a potential new target for anti-anxiety drugs that avoids the drowsiness and other side effects that come with the standard treatments. The target is an integral part of the body’s internal clock, and in tests in mice, compounds aimed at it reduced measures of anxiety while keeping the mice awake. The possibilities show how basic science questions, such as how the body produces sleep and internal rhythms, could have clinical applications. But it’s important to remember that it’s a long way between mice and people. The proteins REV-ERB alpha and REV-ERB beta are found in cell nuclei throughout the body. These proteins are receptors that sense levels of heme, subsections of chemicals in the body containing iron atoms. Levels of heme rise and fall based on a cell’s activity. REV-ERB responds to these heme level changes by controlling the activation of genes within the cell’s nucleus that govern the cell’s 24-hour internal clock. This circadian rhythm plays an important role in controlling our sleep. © Society for Science & the Public 2000 - 2015.
By James Gallagher Health editor, BBC News website The key to learning and memory in early life is a lengthy nap, say scientists. Trials with 216 babies up to 12 months old indicated they were unable to remember new tasks if they did not have a lengthy sleep soon afterwards. The University of Sheffield team suggested the best time to learn may be just before sleep and emphasised the importance of reading at bedtime. Experts said sleep may be much more important in early years than at other ages. People spend more of their time asleep as babies than at any other point in their lives. Yet the researchers, in Sheffield and Ruhr University Bochum, in Germany, say "strikingly little is known" about the role of sleep in the first year of life. Learn, sleep, repeat They taught six- to 12-month-olds three new tasks involving playing with hand puppets. Half the babies slept within four hours of learning, while the rest either had no sleep or napped for fewer than 30 minutes. The next day, the babies were encouraged to repeat what they had been taught. The results, published in Proceedings of the National Academy of Sciences, showed "sleeping like a baby" was vital for learning. On average one-and-a-half tasks could be repeated after having a substantial nap. Yet zero tasks could be repeated if there was little sleep time. Dr Jane Herbert, from the department of psychology at the University of Sheffield, told the BBC News website: "Those who sleep after learning learn well, those not sleeping don't learn at all." © 2015 BBC
ARE you spending enough time in the sun? As well as keeping our bones strong, vitamin D – the hormone our skin makes when exposed to ultraviolet rays – may also help regulate our body clocks. We all have a small group of "clock genes" which switch on and off during the day. As a result, the levels of the proteins they code for rise and fall over a 24-hour period. Enforced routines such as night shift work can play havoc with our health – increasing our risk of a stroke, for example. To find out whether a lack of vitamin D might be responsible, Sean-Patrick Scott and his colleagues at the Monterrey Institute of Technology and Higher Education in Mexico looked at the behaviour of two clock genes in human fat cells. When the cells were immersed in blood serum, they acted as they would in the body: the clock genes' activity oscillated over a 24-hour period. Dosing the cells with vitamin D instead produced the same effect. No such effect was seen in cells placed inside a nutrient broth. "Vitamin D synchronises the cells," says Scott. "Our results explain some of the benefits of sunlight," he says. "Vitamin D is one of the ways we might be able to maintain circadian rhythms in the body." Julia Pakpoor of the University of Oxford says clinical trials are needed to confirm the effect in people, but she adds, "We should all make sure we are vitamin D replete regardless." The work was presented at the World Stem Cell Summit in San Antonio, Texas, last month. © Copyright Reed Business Information Ltd.
Keyword: Biological Rhythms
Link ID: 20454 - Posted: 01.06.2015
By Nicholas Bakalar Planning to read in bed tonight? It may be better to read an actual book instead of an e-book reader. A small study has found that reading light-emitting electronic devices before bedtime is a recipe for poor sleep. Researchers randomly assigned 12 healthy young adults to one of two activities: reading a light-emitting e-book in a dimly lit room for about four hours before bedtime on five consecutive evenings, or reading a printed book for the same amount of time. All participants did both tasks. The researchers took blood samples to measure melatonin levels, and electronically tracked how long it took to fall asleep and how much time was spent in each sleep stage. The study, done at Brigham and Women’s Hospital in Boston, is online in the Proceedings of the National Academy of Sciences. Compared with a printed book, a light-emitting e-book decreased sleepiness, reduced REM sleep (often called dream sleep), and substantially suppressed the normal bedtime rise of melatonin, the hormone that regulates the sleep and wake cycle. The e-book users took longer to fall asleep and felt sleepier in the morning. “Much more has to be known about the kind of impact these devices have on our health and well-being,” said the lead author, Anne-Marie Chang, an assistant professor of biobehavioral health at Penn State. “The technology moves quickly, and the science lags.” © 2014 The New York Times Company
By James Gallagher Health editor, BBC News website Higher rates of obesity and ill-health have been found in shift workers than the general population. Health Survey for England data showed they were in worse health despite often being young. The lead researcher told the BBC that the rise of zero-hours contracts may be increasing the numbers doing shift work and could raise "pretty serious problems" for the nation's health. Scientists said it was "fairly clear now" that shift work was unhealthy. The report, by the Health and Social Care Information Centre, showed 33% of men and 22% of women of working age were doing shift work. They defined shifts as employment outside 0700-1900. Rachel Craig, the research director for the Health Survey for England, told the BBC: "Overall, people who are doing shift work are not quite as healthy as their counterparts doing regular working hours." The data showed 30% of shift workers were obese, compared with 24% of men and 23% of women doing normal hours. Meanwhile, 40% of men and 45% of women on shifts had long-standing health conditions such as back-pain, diabetes or chronic obstructive pulmonary disease compared with 36% and 39% of the rest of the population. Younger people Shift working is most common in the 16-24 age group with nearly half of men and a third of women having this working pattern. The rates fell with age so that fewer than a third of men and a fifth of women were working shifts after the age of 55. Ms Craig said that, overall, young people should be in better health: "You'd expect less ill-health and fewer long-standing conditions that reflect lifestyle like obesity, so it makes it an even stronger relationship [between shifts and poor health]." BBC © 2014
By Nicholas Bakalar Poor sleep in older adults may be linked to brain changes associated with dementia, a new study has found. Researchers studied 167 men who underwent sleep tests in 1999 and died by 2010. The study, in Neurology, recorded sleep duration, periods of waking up and episodes of apnea, and used pulse oximetry to measure oxygen saturation of their blood. On autopsy, they found that those in the highest one-quarter for duration of sleep at oxygen saturation of less than 95 percent were almost four times as likely to have higher levels microinfarcts, small areas of dead tissue caused by deprivation of blood supply, as those in the lowest one-quarter. Compared with those in the lowest 25 percent for duration of slow-wave (deep) sleep, those in the highest one-quarter were about a third as likely to have moderate or high levels of generalized brain atrophy. “Prior studies have shown an association between certain types of sleep disturbance and dementia,” said the lead author, Dr. Rebecca P. Gelber, an epidemiologist with the Veterans Administration in Hawaii. “These lesions may help explain the association.” © 2014 The New York Times Company
Kelly Servick* Anesthesiologists and surgeons who operate on children have been dogged by a growing fear—that being under anesthesia can permanently damage the developing brain. Although the few studies of children knocked out for surgeries have been inconclusive, evidence of impaired development in nematodes, zebrafish, rats, guinea pigs, pigs, and monkeys given common anesthetics has piled up in recent years. Now, the alarm is reaching a tipping point. “Anything that goes from [the roundworm] C. elegans to nonhuman primates, I've got to worry about,” Maria Freire, co-chair of the U.S. Food and Drug Administration (FDA) science advisory board, told attendees at a meeting the agency convened here last month to discuss the issue. The gathering came as anesthesia researchers and regulators consider several moves to address the concerns: a clinical trial of anesthetics in children, a consensus statement about their possible risks, and an FDA warning label on certain drugs. But each step stirs debate. Many involved in the issue are reluctant to make recommendations to parents and physicians based on animal data alone. At the same time, more direct studies of anesthesia's risks in children are plagued by confounding factors, lack of funding, and ethical issues. “We have to generate—very quickly—an action item, because I don't think the status quo is acceptable,” Freire said at the 19 November meeting. “Generating an action item without having the data is where things become very, very tricky.” © 2014 American Association for the Advancement of Science
By CATHERINE SAINT LOUIS Nearly 55 percent of infants nationwide are put to bed with soft blankets or covered by a comforter, even though such bedding raises the chances of suffocation or sudden infant death syndrome, federal researchers reported Monday. Their study, published in the journal Pediatrics, is the first to estimate how many infants sleep with potentially hazardous quilts, bean bags, blankets or pillows. Despite recommendations to avoid putting anything but a baby in a crib, two-thirds of black and Latino parents still use bedding that is both unnecessary and unsafe, the study also found. “I was startled a little bit by the number of people still using bedding in the sleep area,” said Dr. Michael Goodstein, a neonatologist in York, Pa., who serves on a task force on sleep-related infant deaths at the American Academy of Pediatrics. “Sleeping face down on soft bedding increases the risks of SIDS 21-fold.” Among the risk factors for SIDS, “bedding has fallen through the cracks,” said Dr. Thomas G. Keens, the chairman of the California SIDS Advisory Council. “This article is a wake-up call.” The new analysis looked at data gathered from 1993 to 2010 in the National Infant Sleep Position Study, which surveyed a random sample of nearly 19,000 parents by telephone. Use of infant bedding declined roughly 23 percent annually from 1993 to 2000. In recent years, however, the declines have slowed or stalled entirely. From 2001 to 2010, use of inappropriate bedding for white and Hispanic infants declined just 5 to 7 percent annually. There was no decline in the use of such bedding for black infants. Parents in the new study were not asked their reasons for using bedding. Previous research has found that they worry infants will be cold, or that the crib mattress is too hard. © 2014 The New York Times Company
More than 40 percent of infants in a group who died of sudden infant death syndrome (SIDS) were found to have an abnormality in a key part of the brain, researchers report. The abnormality affects the hippocampus, a brain area that influences such functions as breathing, heart rate, and body temperature, via its neurological connections to the brainstem. According to the researchers, supported by the National Institutes of Health, the abnormality was present more often in infants who died of SIDS than in infants whose deaths could be attributed to known causes. The researchers believe the abnormality may destabilize the brain’s control of breathing and heart rate patterns during sleep, or during the periodic brief arousals from sleep that occur throughout the night. “The new finding adds to a growing body of evidence that brain abnormalities may underlie many cases of sudden infant death syndrome,” said Marian Willinger, Ph.D, special assistant for SIDS at NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development, which funded the study. “The hope is that research efforts in this area eventually will provide the means to identify vulnerable infants so that we’ll be able to reduce their risk for SIDS.” SIDS is the sudden death of an infant younger than 1 year of age that is still unexplained after a complete post mortem investigation by a coroner or medical examiner. This investigation includes an autopsy, a review of the death scene, and review of family and medical histories. In the United States, SIDS is the leading cause of death between one month and one year of age. The deaths are associated with an infant’s sleep period.
By Agata Blaszczak-Boxe When it comes to lab animal welfare, rats and mice aren’t the only creatures of concern. In 2013, the European Union mandated that cephalopods—a group that includes octopuses and squid—be treated humanely when used for scientific research. In response, researchers have figured out how to anesthetize octopuses so the animals do not feel pain while being transported and handled during scientific experiments, for instance those examining their behavior, physiology, and neurobiology, as well as their use in aquaculture. In a study published online this month in the Journal of Aquatic Animal Health, researchers report immersing 10 specimens of the common octopus (Octopus vulgaris) in seawater with isoflurane, an anesthetic used in humans. They gradually increased the concentration of the substance from 0.5% to 2%. The investigators found that the animals lost the ability to respond to touch and their color paled, which means that their normal motor coordination of color regulation by the brain was lost, concluding that the animals were indeed anesthetized. The octopuses then recovered from the anesthesia within 40 to 60 minutes of being immersed in fresh seawater without the anesthetic, as they were able to respond to touch again and their color was back to normal. The researchers captured the anesthetization process on video, shown above. © 2014 American Association for the Advancement of Science.
Keyword: Animal Rights
Link ID: 20311 - Posted: 11.15.2014
By Dr. Catherine A. Madison “Now why did I walk into this room? Oh, yes, looking for my …” This scenario, familiar to many, is most often a sign of normal aging — or of having too much on our minds. But when these events seem to be happening frequently, is it a more serious problem, such as Alzheimer’s disease or another dementia? Even more importantly, are there good health habits that can help lower the risk of these neurodegenerative conditions? Research continues to demonstrate that healthy lifestyles lower one’s risk of developing cognitive decline later in life. Wise food choices and lots of exercise are a good base, along with learning new material and keeping socially connected. But another key element to brain health is good sleep. We may take sleep for granted, but research suggests this is not a passive process. There is a growing consensus that sleep is linked to learning, memory, nerve cell remodeling and repair. Evidence also suggests lack of sleep can contribute to mood and immune disorders, as well as to a decline in overall health. Most of us have read the dos and don’ts of good sleep hygiene: avoid napping, don’t drink alcohol or caffeine close to bedtime, avoid late-evening exercise and sleep in a room that is quiet, dark and cool. We’ve also been told about sleep cycles, in which we typically progress from light sleep early in the night to slow wave sleep with rapid eye movement, or REM, later on. We need a balance of sleep cycles for optimal health.
By James Gallagher Health editor, BBC News website Working antisocial hours can prematurely age the brain and dull intellectual ability, scientists warn. Their study, in the journal Occupational and Environmental Medicine, suggested a decade of shifts aged the brain by more than six years. There was some recovery after people stopped working antisocial shifts, but it took five years to return to normal. Experts say the findings could be important in dementia, as many patients have disrupted sleep. The body's internal clock is designed for us to be active in the day and asleep at night. The damaging effects on the body of working against the body clock, from breast cancer to obesity, are well known. Now a team at the University of Swansea and the University of Toulouse has shown an impact on the mind as well. Three thousand people in France performed tests of memory, speed of thought and wider cognitive ability. The brain naturally declines as we age, but the researchers said working antisocial shifts accelerated the process. Those with more than 10 years of shift work under their belts had the same results as someone six and a half years older. The good news is that when people in the study quit shift work, their brains did recover. Even if it took five years. Dr Philip Tucker, part of the research team in Swansea, told the BBC: "It was quite a substantial decline in brain function, it is likely that when people trying to undertake complex cognitive tasks then they might make more mistakes and slip-ups, maybe one in 100 makes a mistake with a very large consequence, but it's hard to say how big a difference it would make in day-to-day life." BBC © 2014
By Paula Span First, an acknowledgment: Insomnia bites. S. Bliss, a reader from Albuquerque, comments that even taking Ativan, he or she awakens at 4:30 a.m., can’t get back to sleep and suffers “a state of sleep deprivation and eventually a kind of walking exhaustion.” Molly from San Diego bemoans “confusion, anxiety, exhaustion, depression, loss of appetite, frankly a loss of will to go on,” all consequences of her sleeplessness. She memorably adds, “Give me Ambien or give me death.” Marciacornute reports that she’s turned to vodka (prompting another reader to wonder if Medicare will cover booze). After several rounds of similar laments here (and not only here; insomnia is prevalent among older adults), I found the results of a study by University of Chicago researchers particularly striking. What if people who report sleep problems are actually getting enough hours of sleep, overall? What if they’re not getting significantly less sleep than people who don’t complain of insomnia? Maybe there’s something else going on. It has always been difficult to ascertain how much people sleep; survey questions are unreliable (how can you tell when you’ve dozed off?), and wiring people with electrodes creates such an abnormal situation that the results may bear little resemblance to ordinary nightlife. Enter the actigraph, a wrist-motion monitor. “The machines have gotten better, smaller, less clunky and more reliable,” said Linda Waite, a sociologist and a co-author of the study. By having 727 older adults across the United States (average age: almost 72) wear actigraphs for three full days, Dr. Waite and her colleagues could tell when subjects were asleep and when they weren’t. Then they could compare their reported insomnia to their actual sleep patterns. Overall, in this random sample, taken from an ongoing national study of older adults, people didn’t appear sleep-deprived. They fell asleep at 10:27 p.m. on average, and awakened at 6:22 a.m. After subtracting wakeful periods during the night, they slept an average seven and a quarter hours. But averages don’t tell us much, so let’s look more closely at their reported insomnia. “What was surprising to us is that there’s very little association between people’s specific sleep problems and what the actigraph shows,” Dr. Waite said. © 2014 The New York Times Company
Scientists say they have identified the underlying reason why some people are prone to the winter blues, or seasonal affective disorder (SAD). People with Sad have an unhelpful way of controlling the "happy" brain signalling compound serotonin during winter months, brain scans reveal. As the nights draw in, production of a transporter protein ramps up in Sad, lowering available serotonin. The work will be presented this week at a neuropsychopharmacology conference. The University of Copenhagen researchers who carried out the trial say their findings confirm what others have suspected - although they only studied 11 people with Sad and 23 healthy volunteers for comparison. Using positron emission tomography (PET) brain scans, they were able to show significant summer-to-winter differences in the levels of the serotonin transporter (SERT) protein in Sad patients. The Sad volunteers had higher levels of SERT in the winter months, corresponding to a greater removal of serotonin in winter, while the healthy volunteers did not. Winter depression Lead researcher, Dr Brenda Mc Mahon, said: "We believe that we have found the dial the brain turns when it has to adjust serotonin to the changing seasons. BBC © 2014
By Jane E. Brody Within a week of my grandsons’ first year in high school, getting enough sleep had already become an issue. Their concerned mother questioned whether lights out at midnight or 1 a.m. and awakening at 7 or 7:30 a.m. to get to school on time provided enough sleep for 14-year-olds to navigate a demanding school day. The boys, of course, said “yes,” especially since they could “catch up” by sleeping late on weekends. But the professional literature on the sleep needs of adolescents says otherwise. Few Americans these days get the hours of sleep optimal for their age, but experts agree that teenagers are more likely to fall short than anyone else. Researchers report that the average adolescent needs eight and a half to nine and a half hours of sleep each night. But in a poll taken in 2006 by the National Sleep Foundation, less than 20 percent reported getting that much rest on school nights. With the profusion of personal electronics, the current percentage is believed to be even worse. A study in Fairfax, Va., found that only 6 percent of children in the 10th grade and only 3 percent in the 12th grade get the recommended amount of sleep. Two in three teens were found to be severely sleep-deprived, losing two or more hours of sleep every night. The causes can be biological, behavioral or environmental. And the effect on the well-being of adolescents — on their health and academic potential — can be profound, according to a policy statement issued in August by the American Academy of Pediatrics. “Sleep is not optional. It’s a health imperative, like eating, breathing and physical activity,” Dr. Judith A. Owens, the statement’s lead author, said in an interview. “This is a huge issue for adolescents.” © 2014 The New York Times Company
By Benedict Carey Sleep. Parents crave it, but children and especially teenagers, need it. When educators and policymakers debate the relationship between sleep schedules and school performance and — given the constraints of buses, sports and everything else that seem so much more important — what they should do about it, they miss an intimate biological fact: Sleep is learning, of a very specific kind. Scientists now argue that a primary purpose of sleep is learning consolidation, separating the signal from the noise and flagging what is most valuable. School schedules change slowly, if at all, and the burden of helping teenagers get the sleep they need is squarely on parents. Can we help our children learn to exploit sleep as a learning tool (while getting enough of it)? Absolutely. There is research suggesting that different kinds of sleep can aid different kinds of learning, and by teaching “sleep study skills,” we can let our teenagers enjoy the sense that they’re gaming the system. Start with the basics. Sleep isn’t merely rest or downtime; the brain comes out to play when head meets pillow. A full night’s sleep includes a large dose of several distinct brain states, including REM sleep – when the brain flares with activity and dreams – and the netherworld of deep sleep, when it whispers to itself in a language that is barely audible. Each of these states developed to handle one kind of job, so getting sleep isn’t just something you “should do” or need. It’s far more: It’s your best friend when you want to get really good at something you’ve been working on. So you want to remember your Spanish vocabulary (or “How I Met Your Mother” trivia or Red Sox batting averages)? © 2014 The New York Times Company
By CATHERINE SAINT LOUIS Many cases of so-called crib death, about one in eight, occur among infants who have been placed on sofas, researchers reported on Monday. Dr. Jeffrey Colvin, a pediatrician at Children’s Mercy Hospital in Kansas City, Mo., and his colleagues analyzed data on 7,934 sudden infant deaths in 24 states, comparing those that occurred on sofas with those in cribs, bassinets or beds. Previous research had shown that couches were particularly hazardous for infants. The new analysis, published in the journal Pediatrics, tried to identify factors significant in these deaths. “It’s not only one risk that’s higher relative to other sleep environments,” said Barbara Ostfeld, a professor of pediatrics at Rutgers Robert Wood Johnson Medical School who was not involved in the new study. “It’s multiple risks.” Nearly three-quarters of the deaths occurred among infants age 3 months or younger, the researchers found. Pediatricians have long advised putting infants to sleep only on their backs, alone and on a firm, flat surface without a pillow. The new study found parents were more likely to lay their infants face down on a sofa than, for instance, face down in a crib. There’s a “fallacy that if I’m awake or watching, SIDS won’t happen,” Dr. Colvin said, referring to sudden infant death syndrome. © 2014 The New York Times Company
BY Bethany Brookshire We all need sleep, but attaining it can be delicate. Insomniacs can’t fall or stay asleep. Travelers suffer from jetlag. Anxiety keeps people up at night. Or maybe it’s just that jackhammer running across the street keeping your eyes open. Some people turn to earplugs, dark curtains or alcohol to soothe them to sleep. But others go to the supplement aisle and pick up melatonin. The hormone melatonin is secreted from our brains at night and helps regulate sleep. But this chemical is not restricted to humans, or even to mammals. The roots of melatonin’s role in our nightly slumbers go back much further in evolutionary history. A new paper focuses in on the role of melatonin in tiny marine creatures called zooplankton. It turns out that these animals use melatonin just as much as we do, suggesting that the origins of sleeplike behavior may lie under the sea. “For every system and feature that makes a human or other animal today, you can ask the question: Where did it start? How did it begin? What was its first role and function, and how did it become more complex?” says study coauthor Detlev Arendt, a zoologist at the University of Heidelberg in Germany. Arendt’s laboratory has been studying the answers to these questions in the marine ragworm Platynereis dumerilii. This unassuming, centipede-like, ocean-dwelling worm produces larvae that float through the open water as zooplankton. These small larvae propel themselves up and down in the water column with movements of their cilia, slender, hair-like appendages that protrude out from the organisms. © Society for Science & the Public 2000 - 2014.
By CLAIRE MALDARELLI Whether it’s lying wide awake in the middle of the night or falling asleep at an international business meeting, many of us have experienced the funk of jet lag. New research has uncovered some of the mysteries behind how our cells work together to maintain one constant daily rhythm, offering the promise of defense against this disorienting travel companion. Many organisms, including humans and fruit flies, have pacemaker neurons — specialized cells in the brain that have their own molecular clocks and oscillate in 24-hour cycles. But in order for an organism to regulate itself, all of these internal clocks must tick together to create one master clock. While scientists understood how individual neurons set their own clock, they didn’t know how that master clock was set. Working with young fruit flies, whose neuronal system is simpler than adults with fewer cells and easier to study, the researchers found that two types of neurons, which they called dawn cells and dusk cells, maintain a continuous cycle. As the sun rises, special “timeless” proteins, as they’re called, help the dawn cells to first signal to each other and then signal to the dusk cells. Then as the sun sets, proteins help the dusk cells signal to each other and then signal back to the dawn cells. Each signal tells the cells to synchronize with each other. Together, these two distinct signals drive the daily sleep and wake cycle. “This really shifts our view of these cells as super strong, independent oscillators to much more of a collective group working together to keep time,” said Justin Blau, a neurobiologist at New York University and co-author of the study. © 2014 The New York Times Company
Carl Zimmer As much as we may try to deny it, Earth’s cycle of day and night rules our lives. When the sun sets, the encroaching darkness sets off a chain of molecular events spreading from our eyes to our pineal gland, which oozes a hormone called melatonin into the brain. When the melatonin latches onto neurons, it alters their electrical rhythm, nudging the brain into the realm of sleep. At dawn, sunlight snuffs out the melatonin, forcing the brain back to its wakeful pattern again. We fight these cycles each time we stay up late reading our smartphones, suppressing our nightly dose of melatonin and waking up grumpy the next day. We fly across continents as if we could instantly reset our inner clocks. But our melatonin-driven sleep cycle lags behind, leaving us drowsy in the middle of the day. Scientists have long wondered how this powerful cycle got its start. A new study on melatonin hints that it evolved some 700 million years ago. The authors of the study propose that our nightly slumbers evolved from the rise and fall of our tiny oceangoing ancestors, as they swam up to the surface of the sea at twilight and then sank in a sleepy fall through the night. To explore the evolution of sleep, scientists at the European Molecular Biology Laboratory in Germany study the activity of genes involved in making melatonin and other sleep-related molecules. Over the past few years, they’ve compared the activity of these genes in vertebrates like us with their activity in a distantly related invertebrate — a marine worm called Platynereis dumerilii. The scientists studied the worms at an early stage, when they were ball-shaped 2-day-old larvae. The ocean swarms with juvenile animals like these. Many of them spend their nights near the ocean surface, feeding on algae and other bits of food. Then they spend the day at lower depths, where they can hide from predators and the sun’s ultraviolet rays. © 2014 The New York Times Company