Chapter 14. Biological Rhythms, Sleep, and Dreaming
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By Alice Klein The debate has finally been put to bed. Wearable brainwave recorders confirm that birds do indeed sleep while flying, but only for brief periods and usually with one half of their brain. We know several bird species can travel vast distances non-stop, prompting speculation that they must nap mid-flight. Great frigatebirds, for example, can fly continuously for up to two months. On the other hand, the male sandpiper, for one, can largely forgo sleep during the breeding season, hinting that it may also be possible for birds to stay awake during prolonged trips. To settle this question, Niels Rattenborg at the Max Planck Institute for Ornithology in Seewiesen, Germany, and his colleagues fitted small brain activity monitors and movement trackers to 14 great frigatebirds. During long flights, the birds slept for an average of 41 minutes per day, in short episodes of about 12 seconds each. By contrast, they slept for more than 12 hours per day on land. Frigatebirds in flight tend to use one hemisphere at a time to sleep, as do ducks and dolphins, but sometimes they used both. “Some people thought that all their sleep would have to be unihemispheric otherwise they would drop from the sky,” says Rattenborg. “But that’s not the case – they can sleep with both hemispheres and they just continue soaring.” Sleep typically took place as the birds were circling in rising air currents, when they did not need to flap their wings. © Copyright Reed Business Information Ltd.
Aaron E. Carroll I remember thinking, after my pregnant wife’s water broke, minutes after I went to bed, anguishing really, over one thought as we drove to the hospital: “I’m never going to be well rested again.” If there’s one things all new parents wish for, it’s a good night’s sleep. Unfortunately, infants sometimes make that impossible. They wake up repeatedly, needing to be fed, changed and comforted. Eventually, they reach an age when they should sleep through the night. Some don’t, though. What to do with them continues to be a topic of a heated debate in parenting circles. One camp believes that babies should be left to cry it out. These people place babies in their cribs at a certain time, after a certain routine, and don’t interfere until the next morning. No matter how much the babies scream or cry, parents ignore them. After all, if babies learn that tantrums lead to the appearance of a loved one, they will continue that behavior in the future. The official name for this intervention is “Extinction.” The downside, of course, is that it’s unbelievably stressful for parents. Many can’t do it. And not holding fast to the plan can make everything worse. Responding to an infant’s crying after an extended period of time makes the behavior harder to extinguish. To a baby, it’s like a slot machine that hits just as you’re ready to walk away; it makes you want to play more. A modification of this strategy is known as “Graduated Extinction.” Parents allow their infant to cry it out for a longer period each night, until infants eventually put themselves to sleep. On the first night, for instance, parents might commit to not entering the baby’s room for five minutes. The next night, 10 minutes. Then 15, and so on. Or, they could increase the increments on progressive checks each night. When they do go in the room, it’s only to check and make sure the baby is O.K. – no picking up or comforting. This isn’t meant to be a reward for crying, but to allow parents to be assured that nothing is wrong. © 2016 The New York Times Company
By Richard Kemeny Sleep is essential for memory. Mounting evidence continues to support the notion that the nocturnal brain replays, stabilizes, reorganizes, and strengthens memories while the body is at rest. Recently, one particular facet of this process has piqued the interest of a growing group of neuroscientists: sleep spindles. For years these brief bursts of brain activity have been largely ignored. Now it seems that examining these neuronal pulses could help researchers better understand—perhaps even treat—cognitive impairments. Sleep spindles are a defining characteristic of stage 2 non-rapid eye movement (NREM) sleep. These electrical bursts between 10-16 Hz last only around a second, and are known to occur in the human brain thousands of times per night. Generated by a thin net of neurons enveloping the thalamus, spindles appear across several regions of the brain, and are thought to perform various functions, including maintaining sleep in the face of disturbances in the environment. It appears they are also a fundamental part of the process by which the human brain consolidates memories during sleep. A memory formed during the day is stored temporarily in the hippocampus, before being spontaneously replayed during the night. Information about the memory is distributed out and integrated into the neocortex through an orchestra of slow-waves, spindles, and rapid hippocampal ripples. Spindles, it seems, could be a guiding force—providing the plasticity and coordination needed for this delicate, interregional transfer of information. © 1986-2016 The Scientist
By Emma Bryce In 1999, neuroscientist Gero Miesenböck dreamed of using light to expose the brain's inner workings. Two years later, he invented optogenetics, a technique that fulfils this goal: by genetically engineering cells to contain proteins that make them light-responsive, Miesenböck found he could shine light at the brain and trigger electrical activity in those cells. This technique gave scientists the tools to activate and control specific cell populations in the brain, for the first time. For example, Miesenböck, who directs the Centre for Neural Circuits and Behaviour at the University of Oxford, first used optogenetics to activate courtship responses in fruit flies, and even make headless flies take flight - groundbreaking experiments that allowed him to examine, in unprecedented detail, how neurons drive behaviour. Gero Miesenböck: There was almost a "eureka" moment. As is often the case, you tend to have your best ideas when you're not trying to have them: suddenly I had this idea - which I must have been incubating for a long time, because I was thinking about manipulating neurons in the brain genetically to emit light so I could visualise their activity. Suddenly I thought, "What if we just turn the thing upside down, and instead of reading activity, write activity using light and genetics?" That was the real breakthrough idea, and then of course came the big challenge of having to make it work. Brains are composed of many different kinds of nerve cells, and they are genetically distinct from one another. To deconstruct how the brain works we need to pinpoint the roles these individual classes of cells play in processing information. Optogenetics uses the genetic signatures that define individual cell types to address them selectively in the intact brain - that's the "genetics" component. The "opto" component is to use these genetic signatures to place light-sensitive molecules that are encoded in DNA within these cells.
Link ID: 22469 - Posted: 07.23.2016
You drift off to dreamland just fine but then something, a noise, a partner's tossing and turning, jars you awake. Now your mind races with an ever expanding to-do list of worries that you can't shut off. When the alarm buzzes, you start the day feeling grouchy and slightly dazed. Nearly six in 10 Canadians say they wake up feeling tired. About 40 per cent of Canadians will exhaust themselves with a sleep disorder at some point in their lifetime, studies suggest. It's common for people to wake up in the middle of the night. What's important is not to let it snowball, sleep specialists say. Our sleep cycles include brief periods of wakefulness but deep sleep makes us forget about these awakenings. "It's normal to have one or two a night," said Dr. Brian Murray, a sleep neurologist at Sunnybrook Health Sciences Centre and a professor at the University of Toronto. "It's when it's multiple that I worry." Sleep experts say if someone wakes up multiple times a night, it's a red flag. Chronic sleep problems are linked to heart disease, high blood pressure and some cancers. It can also affect hormone levels, which increases the risk of obesity and Type 2 diabetes, sleep specialists say. Julie Snyder of Toronto said she has stretches of days or weeks when she'll consistently wake up at 1:15 a.m., and again at 4 a.m. The broken sleep leaves her feeling short on patience. ©2016 CBC/Radio-Canada.
Link ID: 22463 - Posted: 07.21.2016
Rachel Ehrenberg The brain doesn’t really go out like a light when anesthesia kicks in. Nor does neural activity gradually dim, a new study in monkeys reveals. Rather, intermittent flickers of brain activity appear as the effects of an anesthetic take hold. Some synchronized networks of brain activity fall out of step as the monkeys gradually drift from wakefulness, the study showed. But those networks resynchronized when deep unconsciousness set in, researchers reported in the July 20 Journal of Neuroscience. That the two networks behave so differently during the drifting-off stage is surprising, says study coauthor Yumiko Ishizawa of Harvard Medical School and Massachusetts General Hospital. It isn’t clear what exactly is going on, she says, except that the anesthetic’s effects are a lot more complex than previously thought. Most studies examining the how anesthesia works useelectroencephalograms, or EEGs, which record brain activity using electrodes on the scalp. The new study offers unprecedented surveillance by eavesdropping via electrodes implanted inside macaque monkeys’ brains. This new view provides clues to how the brain loses and gains consciousness. “It’s a very detailed description of something we know very little about,” says cognitive neuroscientist Tristan Bekinschtein of the University of Cambridge, who was not involved with the work. Although the study is elegant, it isn’t clear what to make of the findings, he says. “These are early days.” |© Society for Science & the Public 2000 - 2016.
Link ID: 22457 - Posted: 07.20.2016
By JOANNA KLEIN Jet lag may be the worst part of traveling. And it hits many people harder traveling east than west. Why they feel this way is unclear. But scientists recently developed a model that mimics special time-keeping cells in the body and offers a mathematical explanation for why traveling from west to east feels so much worse. It also offers insights on recovering from jet lag. Deep inside the brain, in a region called the hypothalamus (right above where our optic nerves cross) the internal clock is ticking. And approximately every 24 hours, 20,000 special pacemaker cells that inhabit this area, known as the superchiasmatic nucleus, synchronize, signaling to the rest of the body whether it’s night or day. These cells know which signal to send because they receive light input from our environments — bright says wake, dark says sleep. But when you travel across multiple time zones, like flying from New York to Moscow, those little pacemaker cells that thought they knew the routine scramble around confused before they can put on their show. The whole body feels groggy because it’s looking for the time and can’t find it. The result: jet lag. Most of our internal clocks are a little bit slow, and in the absence of consistent light cues — like when you travel across time zones — the pacemaker cells in your body want to have a longer day, said Michelle Girvan, a physicist at the University of Maryland who worked on the model published in the journal Chaos on Tuesday. “This is all because the body’s internal clock has a natural period of slightly longer than 24 hours, which means that it has an easier time traveling west and lengthening the day than traveling east and shortening the day,” Dr. Girvan said. © 2016 The New York Times Company
Keyword: Biological Rhythms
Link ID: 22446 - Posted: 07.16.2016
Rebecca Boyle Eliane Lucassen works the night shift at Leiden University Medical Center in the Netherlands, beginning her day at 6 p.m. Yet her own research has shown that this schedule might cause her health problems. “It’s funny,” the medical resident says. “Here I am, spreading around that it’s actually unhealthy. But it needs to be done.” Lucassen and Johanna Meijer, a neuroscientist at Leiden, report today in Current Biology1 that a constant barrage of bright light prematurely ages mice, playing havoc with their circadian clocks and causing a cascade of health problems. Mice exposed to constant light experienced bone-density loss, skeletal-muscle weakness and inflammation; restoring their health was as simple as turning the lights off. The findings are preliminary, but they suggest that people living in cities flooded with artificial light may face similar health risks. “We came to know that smoking was bad, or that sugar is bad, but light was never an issue,” says Meijer. “Light and darkness matter.” Disrupted patterns Many previous studies have hinted at a connection between artificial light exposure and health problems in animals and people2. Epidemiological analyses have found that shift workers have an increased risk of breast cancer3, metabolic syndrome4 and osteoporosis5, 6. People exposed to bright light at night are more likely to have cardiovascular disease and often don’t get enough sleep. © 2016 Macmillan Publishers Limited,
Keyword: Biological Rhythms
Link ID: 22442 - Posted: 07.15.2016
By Clare Wilson It is one of life’s great enigmas: why do we sleep? Now we have the best evidence yet of what sleep is for – allowing housekeeping processes to take place that stop our brains becoming overloaded with new memories. All animals studied so far have been found to sleep, but the reason for their slumber has eluded us. When lab rats are deprived of sleep, they die within a month, and when people go for a few days without sleeping, they start to hallucinate and may have epileptic seizures. One idea is that sleep helps us consolidate new memories, as people do better in tests if they get a chance to sleep after learning. We know that, while awake, fresh memories are recorded by reinforcing connections between brain cells, but the memory processes that take place while we sleep have remained unclear. Support is growing for a theory that sleep evolved so that connections in the brain can be pruned down during slumber, making room for fresh memories to form the next day. “Sleep is the price we pay for learning,” says Giulio Tononi of the University of Wisconsin-Madison, who developed the idea. Now we have the most direct evidence yet that he’s right. Tononi’s team measured the size of these connections or synapses in brain slices taken from mice. The synapses in samples taken at the end of a period of sleep were 18 per cent smaller than those in samples taken from before sleep, showing that the synapses between neurons are weakened during slumber. © Copyright Reed Business Information Ltd.
By Karl Gruber For most birds the night brings a well-deserved rest. But for some, it is time for more risqué activities. Nocturnal birds sing at night – no surprises there – mainly to attract mates or repel rivals, the same reasons other birds sing at daytime. But a small number of species active by day also occasionally sing at night. Why they invest time and energy in such behaviour has been something of a mystery. Now Antonio Celis-Murillo at the Illinois Natural History Survey in Champaign and his colleagues think they have an answer – and it wasn’t what they expected. The team spent two years studying field sparrows, Spizella pusilla, a common bird across eastern North America. Active during the day, these birds are territorial and largely monogamous, though they engage in occasional infidelity. The researchers observed 28 pairs in the wild, recording the songs of territorial males, as well as those of intruder and neighbouring males. They then conducted playback experiments at night, studying the responses of the pairs. “I was surprised to see what these birds were up to,” says Celis-Murillo. The males sing to attract other male’s partners, and these females are all too willing to wake up for a night-time rendezvous. The team also found that males sang more during periods when females were reproductively receptive, and that the females responded to such song more often when they were fertile. The female’s mate didn’t appear to kick up a fuss and counter-sing – which would be expected if nocturnal songs served to repel rivals. © Copyright Reed Business Information Ltd.
Laurel Hamers Even Amelia Earhart couldn’t compete with the great frigate bird. She flew nonstop across the United States for 19 hours in 1932; the frigate bird can stay aloft up to two months without landing, a new study finds. The seabird saves energy on transoceanic treks by capitalizing on the large-scale movement patterns of the atmosphere, researchers report in the July 1 Science. By hitching a ride on favorable winds, the bird can spend more time soaring and less time flapping its wings. “Frigate birds are really an anomaly,” says Scott Shaffer, an ecologist at San Jose State University in California who wasn’t involved in the study. The large seabird spends much of its life over the open ocean. Both juvenile and adult birds undertake nonstop flights lasting weeks or months, the scientists found. Frigate birds can’t land in the water to catch a meal or take a break because their feathers aren’t waterproof, so scientists weren’t sure how the birds made such extreme journeys. Researchers attached tiny accelerometers, GPS trackers and heart rate monitors to great frigate birds flying from a tiny island near Madagascar. By pooling data collected over several years, the team re-created what the birds were doing minute-by-minute over long flights — everything from how often the birds flapped their wings to when they dived for food. © Society for Science & the Public 2000 - 2016.
By Tanya Lewis The human brain may wind down when asleep, but it doesn’t lose all responsiveness. Researchers from the École Normale Supérieure in Paris and their colleagues recently used electroencephalography (EEG) to monitor the brains of volunteers listening to recordings of spoken words, which they were asked to classify as either objects or animals. Participants were able to classify words during light non-REM (NREM) sleep, but not during either deep NREM sleep or REM sleep, according to a study published today (June 14) in The Journal of Neuroscience. “With an elegant experimental design and sophisticated analyses of neural activity, [the authors] demonstrate the extent to which the sleeping brain is able to process sensory information, depending on sleep depth [or] stage,” Thomas Schreiner of the University of Fribourg in Switzerland, who was not involved in the study, wrote in an email to The Scientist. During sleep, the brain is thought to block out external stimuli through a gating mechanism at the level of the thalamus. But experiments dating back to the 1960s have shown that certain types of stimuli, such as hearing one’s name, can filter through and trigger awakening. However, the mechanisms that allow the brain to selectively take in information during sleep remain unknown. “When we fall asleep, it’s pretty similar to a coma because we lose consciousness of our self and of the [outside] world,” study coauthor Thomas Andrillon, a neuroscientist at the École Normale Supérieure, told The Scientist. The question was “whether the brain could still monitor what was going on around, just to be sure the environment was still safe,” he added. © 1986-2016 The Scientist
By Karen Weintraub Many people think they can teach themselves to need less sleep, but they’re wrong, said Dr. Sigrid Veasey, a professor at the Center for Sleep and Circadian Neurobiology at the University of Pennsylvania’s Perelman School of Medicine. We might feel that we’re getting by fine on less sleep, but we’re deluding ourselves, Dr. Veasey said, largely because lack of sleep skews our self-awareness. “The more you deprive yourself of sleep over long periods of time, the less accurate you are of judging your own sleep perception,” she said. Multiple studies have shown that people don’t functionally adapt to less sleep than their bodies need. There is a range of normal sleep times, with most healthy adults naturally needing seven to nine hours of sleep per night, according to the National Sleep Foundation. Those over 65 need about seven to eight hours, on average, while teenagers need eight to 10 hours, and school-age children nine to 11 hours. People’s performance continues to be poor while they are sleep deprived, Dr. Veasey said. Extended vacations are the best times to assess how much sleep you truly need. Once you catch up on lost sleep and are not sleep deprived, the amount you end up sleeping is a good measure how much you need every night. You can ask yourself the questions, “Do you feel that your brain is much sharper, your temper is better, you’re paying attention more effectively? If those answers are yes, than definitely get the sleep,” said Dr. Veasey, who realized -- to her chagrin -- that she needs nine hours of sleep a night to function effectively. Health issues like pain, sleep apnea or autoimmune disease can increase people's need for sleep, said Andrea Meredith, a neuroscientist at the University of Maryland School of Medicine. © 2016 The New York Times Company
Link ID: 22333 - Posted: 06.18.2016
By Ashley P. Taylor Sleep is known to aid memory and learning. For example, people who learn something, sleep on it, and are tested on the material after they wake up tend to perform better than those who remain awake in the interim. Within that general phenomenon, however, there’s a lot of unexplained variation. University of California, Riverside, sleep researcher Sara Mednick wondered “what else might be going during that sleep period that helps people’s memories,” she told The Scientist. As it turns out, activity of the autonomic nervous system (ANS) explains a large part of this variation, Mednick and colleagues show in a paper published today (June 13) in PNAS. The researchers measured not only the electrical activity of the brain during sleep, but also that of the heart, providing an indicator of ANS activity. They found that the beat-to-beat variation in heart rate accounted for much of the previously unexplained variation in how well people performed on memory and creativity tests following a nap. “There is a good possibility that this additional measure [heart-rate variability] may help account for discrepant findings in the sleep-dependent memory consolidation literature,” sleep and cognition researcher Rebecca Spencer of the University of Massachusetts, Amherst, who was not involved in the work, wrote in an email. “Perhaps we put too large of a focus on sleep physiology from the CNS [central nervous system] and ignore a significant role of the ANS.” © 1986-2016 The Scientist
By Ian Randall As if you needed another reason to hate the gym, it now turns out that exercise can exhaust not only your muscles, but also your eyes. Fear not, however, for coffee can perk them right up again. During strenuous exercise, our muscles tire as they run out of fuel and build up waste products. Muscle performance can also be affected by a phenomenon called “central fatigue,” in which an imbalance in the body’s chemical messengers prevents the central nervous system from directing muscle movements effectively. It was not known, however, whether central fatigue might also affect motor systems not directly involved in the exercise itself—such as those that move the eyes. To find out, researchers gave 11 volunteers a carbohydrate solution either with a moderate dose of caffeine—which is known to stimulate the central nervous system—or as a placebo without, during 3 hours of vigorous cycling. After exercising, the scientists tested the cyclists with eye-tracking cameras to see how well their brains could still control their visual system. The team found that exercise reduced the speed of rapid eye movements by about 8%, impeding their ability to capture new visual information. The caffeine—the equivalent of two strong cups of coffee—was sufficient to counteract this effect, with some cyclists even displaying increased eye movement speeds, the team reports today in Scientific Reports. So it might be a good idea to get someone else to drive you home after that marathon. © 2016 American Association for the Advancement of Science.
Link ID: 22243 - Posted: 05.25.2016
Bret Stetka We've all been caught in that hazy tug of war between wakefulness and sleep. But the biology behind how our brains drive us to sleep when we're sleep-deprived hasn't been entirely clear. For the first time scientists have identified the neurons in the brain that appear to control sleep drive, or the growing pressure we feel to sleep after being up for an extended period of time. The findings, published online Thursday by the journal Cell, could lead to better understanding of sleep disorders in humans. And perhaps, one day, if the work all pans out, better treatments for chronic insomnia could be developed. To explore which brain areas might be involved in sleep drive, Johns Hopkins neuroscientist Dr. Mark Wu and his colleagues turned to fruit flies, that long tinkered-with subject of scientific inquiry. Despite our rather obvious physical distinctions, humans and fruit flies – or Drosophila – have a good deal in common when it comes to genes, brain architecture and even behaviors. Included in the study were over 500 strains of fly, each with unique brain activation profiles (meaning certain circuits are more active in certain flies). By employing a genetic engineering technique in which specific groups of neurons can be activated with heat, the researchers were able to monitor the firing of nearly all the major circuits in the fruit fly brain and monitor the resulting effects on sleep. Moreover, the neurons of interest were engineered to glow green when activated allowing specific cells to be identified with fluorescent microscopy. Wu found that activating a group of cells called R2 neurons, which are found in a brain region known as the ellipsoid body, put fruit flies to sleep, even for hours after the neurons were "turned off." © 2016 npr
By Karen Weintraub There are case reports of people with no previously known risks having a heart attack after a nightmare, though they appear to be quite rare. No studies have been done to determine just how rare nightmare-induced heart attacks might be, and experts do not know whether they may result from the pulse-racing effects of the frightening dream itself. Nightmares are more commonly seen in the rapid eye movement, or REM, phase of sleep, which gets longer as the night progresses. Therefore, nightmares are more likely to occur in the early morning hours. Heart attacks, too, are most common in the early morning hours, when internal body clocks start secreting stress hormones and blood pressure tends to rise, said Dr. Mary Ann McLaughlin, a cardiologist at the Icahn School of Medicine at Mount Sinai in New York. If someone is at risk for a heart attack — because of high blood pressure, diabetes, sleep apnea, smoking or other factors — that attack is more likely to occur in the early morning. But “it’s rare for an otherwise healthy person to have a nightmare that causes a heart attack,” said Dr. McLaughlin. Nightmares can be triggered by alcohol, lack of sleep and medications, including some antidepressants and blood pressure medications, she said. Anxiety and depression have also been linked to increased risk of nightmares. On the flip side, patients with heart disease often have sleep apnea, a form of disordered breathing that can lead to fragmented sleep, and potentially more nightmares, said Dr. Neomi Shah, a sleep specialist, also at Mount Sinai. One 2013 study found that apnea patients with regular nightmares woke up more often than those who didn’t. Nightmares disappeared in more than 90 percent of the patients who used a continuous positive airway pressure, or CPAP, machine to treat their apnea. © 2016 The New York Times Company
Link ID: 22232 - Posted: 05.21.2016
Laura Sanders In mice, a long course of antibiotics that wiped out gut bacteria slowed the birth of new brain cells and impaired memory, scientists write May 19 in Cell Reports. The results reinforce evidence for a powerful connection between bacteria in the gut and the brain (SN: 4/2/16, p. 23). After seven weeks of drinking water spiked with a cocktail of antibiotics, mice had fewer newborn nerve cells in a part of the hippocampus, a brain structure important for memory. The mice’s ability to remember previously seen objects also suffered. Further experiments revealed one way bacteria can influence brain cell growth and memory. Injections of immune cells called Ly6Chi monocytes boosted the number of new nerve cells. Themonocytes appear to carry messages from gut to brain, Susanne Wolf of the Max Delbrück Center for Molecular Medicine in Berlin and colleagues found. Exercise and probiotic treatment with eight types of live bacteria also increased the number of newborn nerve cells and improved memory in mice treated with antibiotics. The results help clarify the toll of prolonged antibiotic treatment, and hint at ways to fight back, the authors write. L. Möhle et al. Ly6Chi monocytes provide a link between antibiotic-induced changes in gut microbiota and adult hippocampal neurogenesis. Cell Reports. Vol. 15, May 31, 2016. doi: 10.1016/j.celrep.2016.04.074. © Society for Science & the Public 2000 - 2016
Laura Sanders Brain waves during REM sleep solidify memories in mice, scientists report in the May 13 Science. Scientists suspected that the eye-twitchy, dream-packed slumber known as rapid eye movement sleep was important for memory. But REM sleep’s influence on memory has been hard to study, in part because scientists often resorted to waking people or animals up — a stressful experience that might influence memory in different ways. Richard Boyce of McGill University in Montreal and colleagues interrupted REM sleep in mice in a more delicate way. Using a technique called optogenetics, the researchers blocked a brain oscillation called theta waves in the hippocampus, a brain structure involved in memory, during REM sleep. This light touch meant that the mice stayed asleep but had fewer REM-related theta waves in their hippocampi. Usually, post-learning sleep helps strengthen memories. But mice with disturbed REM sleep had memory trouble, the researchers found. Curious mice will spend more time checking out an object that’s been moved to a new spot than an unmoved object. But after the sleep treatment, the mice seemed to not remember objects’ earlier positions, spending equal time exploring an unmoved object as one in a new place. These mice also showed fewer signs of fear in a place where they had previously suffered shocks. Interfering with theta waves during other stages of sleep didn’t seem to cause memory trouble, suggesting that something special happens during REM sleep. R. Boyce et al. Causal evidence for the role of REM sleep theta rhythm in contextual memory consolidation. Science. Vol. 352, p. 812, May 13, 2016. doi: 10.1126/science.aad5252. © Society for Science & the Public 2000 - 2016.
By David Shultz Did you sleep well? The answer may depend on your age, location and gender. A survey of 5000 sleepers from across the world has revealed that women get the most sleep, particularly those under the age of 25. Daniel Forger at the University of Michigan in Ann Arbor and his team were able to get their huge dataset thanks to Entrain, a smartphone app that people use to track their sleep. With their consent, Forger’s team accessed users’ data on their wake time, bed time, time zone and how much light they were exposed to during the day. Analysing this information, they found that middle-aged men sleep the least, while women under the age of 25 sleep the most. As a whole, women appear to sleep on average for 30 minutes longer than men, thanks to going to bed slightly earlier and waking up slightly later. For an individual, the time they woke up had the strongest link to how much sleep they got, suggesting that having a job that starts early every day can mean that you get less sleep than someone who starts work at a later hour. There were also differences between countries. People in Singapore, for example, sleep for an average of 7.5 hours a night, while Australians get 8.1 hours. Late bedtimes seem to be to blame – people in Singapore tended to stay up until after 11.45 pm each night, while people in Australia were likely to hit the hay closer to 10.45 pm. The team found that, in general, national wake-up times were linked more to daylight hours than bedtimes. This could be because bedtimes are more affected by social factors. © Copyright Reed Business Information Ltd.