Chapter 14. Biological Rhythms, Sleep, and Dreaming
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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.
By ERICA GOODE Horses snooze in their stalls. Fish take their 40 winks floating in place. Dogs can doze anywhere, anytime. And even the lowly worm nods off now and then. All animals, most scientists agree, engage in some form of sleep. But the stages of sleep that characterize human slumber had until now been documented only in mammals and birds. A team of researchers in Germany announced in a report published on Thursday, however, that they had found evidence of similar sleep stages in a lizard: specifically, the bearded dragon, or Pogona vitticeps, a reptile native to Australia and popular with pet owners. Recordings from electrodes implanted in the lizards’ brains showed patterns of electrical activity that resembled what is known as slow-wave sleep and another pattern resembling rapid eye movement, or REM, sleep, a stage of deep slumber associated with brain activity similar to that of waking. Some researchers had argued that these stages were of relatively recent origin in evolutionary terms because they had not been found in more primitive animals like amphibians, fish, reptiles other than birds, and other creatures with backbones. But the new finding, said Gilles Laurent, director of the department of neural systems at the Max Planck Institute for Brain Research and the principal author of the study, “increases the probability that sleep evolved in all these animals from a common ancestor.” He added that it also raised the possibility that staged sleep evolved even earlier and that some version of it might exist in animals like amphibians or fish. The report appeared in Thursday’s issue of the journal Science. Other researchers said the study could help scientists understand more about the purpose and mechanisms of sleep. But the finding, they added, is bound to generate more controversy about whether the resting state of primitive animals is really the same as sleep, and whether the brain activity seen in a lizard can be compared to that in mammals. © 2016 The New York Times Company
Tina Hesman Saey To rewrite an Alanis Morissette song, the brain has a funny way of waking you up (and putting you to sleep). Isn’t it ionic? Some scientists think so. Changes in ion concentrations, not nerve cell activity, switch the brain from asleep to awake and back again, researchers report in the April 29 Science. Scientists knew that levels of potassium, calcium and magnesium ions bathing brain cells changed during sleep and wakefulness. But they thought neurons — electrically active cells responsible for most of the brain’s processing power — drove those changes. Instead, the study suggests, neurons aren’t the only sandmen or roosters in the brain. “Neuromodulator” brain chemicals, which pace neuron activity, can bypass neurons altogether to directly wake the brain or lull it to sleep by changing ion concentrations. Scientists hadn’t found this direct connection between ions and sleep and wake before because they were mostly focused on what neurons were doing, says neuroscientist Maiken Nedergaard, who led the study. She got interested in sleep after her lab at the University of Rochester in New York found a drainage system that washes the brain during sleep (SN: 11/16/13, p. 7).When measuring changes in the fluid between brain cells, Nedergaard and colleagues realized that ion changes followed predictable patterns: Potassium ion levels are high when mice (and presumably people) are awake, and drop during sleep. Calcium and magnesium ions follow the opposite pattern; they are higher during sleep and lower when mice are awake. © Society for Science & the Public 2000 - 2016
Link ID: 22163 - Posted: 04.30.2016
Jon Hamilton People who sustain a concussion or a more severe traumatic brain injury are likely to have sleep problems that continue for at least a year and a half. A study of 31 patients with this sort of brain injury found that 18 months afterward, they were still getting, on average, an hour more sleep each night than similar healthy people were getting. And despite the extra sleep, 67 percent showed signs of excessive daytime sleepiness. Only 19 percent of healthy people had that problem. Surprisingly, most of these concussed patients had no idea that their sleep patterns had changed. "If you ask them, they say they are fine," says Dr. Lukas Imbach, the study's first author and a senior physician at the University Hospital Zurich in Zurich. When Imbach confronts patients with their test results, "they are surprised," he says. The results, published Thursday in the online edition of the journal Neurology, suggest there could be a quiet epidemic of sleep disorders among people with traumatic brain injuries. The injuries are diagnosed in more than 2 million people a year in the United States. Common causes include falls, motor vehicle incidents and assaults. Previous studies have found that about half of all people who sustain sudden trauma to the brain experience sleep problems. But it has been unclear how long those problems persist. "Nobody actually had looked into that in detail," Imbach says. A sleep disorder detected 18 months after an injury will linger for at least two years, and probably much longer, the researchers say. © 2016 npr
Anna Nowogrodzki Prions, the misfolded proteins that are known for causing degenerative illnesses in animals and humans, may have been spotted for the first time in plants. Researchers led by Susan Lindquist, a biologist at the Whitehead Institute for Biomedical Research in Cambridge, Massachusetts, report that they have found a section of protein in thale cress (Arabidopsis) that behaves like a prion when it is inserted into yeast. In plants, the protein is called Luminidependens (LD), and it is normally involved in responding to daylight and controlling flowering time. When a part of the LD gene is inserted into yeast, it produces a protein that does not fold up normally, and which spreads this misfolded state to proteins around it in a domino effect that causes aggregates or clumps. Later generations of yeast cells inherit the effect: their versions of the protein also misfold. This does not mean that plants definitely have prion-like proteins, adds Lindquist — but she thinks that it is likely. “I’d be surprised if they weren’t there,” she says. To prove it, researchers would need to grind up a plant and see whether they could find a protein such as LD in several different folded states, as well as show that any potential prion caused a misfolding cascade when added to a test-tube of protein. Lindquist adds that because she's not a plant scientist — her focus is on using yeast to investigate prions — she hasn't tried these experiments. The study is reported on 25 April in the Proceedings of the National Academy of Sciences1. © 2016 Nature Publishing Group
By Clare Wilson One day, you might be seeing in blue for 24 hours before you have an operation – to prevent organ damage. A study in mice suggests that exposure to blue light reduces a form of organ damage that is common during surgery. Reperfusion injury can happen when blood vessels are temporarily tied off during surgery, or when blocked arteries are surgically widened after a heart attack or stroke. Some damage is caused by a lack of oxygen, and further harm results when oxygen levels rebound, causing cells to become overactive, and triggering an attack by the immune system. But blue light seems to reduce this, in mice at least. Matthew Rosengart of the University of Pittsburgh, Pennsylvania, and his team have found that when mice are exposed to blue light for 24 hours before the blood supply to their liver or kidney is temporarily tied off, there is less reperfusion injury than if the mice are exposed to other types of light. “That’s pretty remarkable,” says Jack Pickard, a reperfusion researcher at University College London. Further tests showed that blue light seems to dampen down the sympathetic nervous system, which is involved in mammal stress responses. In turn, this reduced the activity of immune cells called neutrophils, which are involved in inflicting the damage of a reperfusion injury. © Copyright Reed Business Information Ltd.
Keyword: Biological Rhythms
Link ID: 22145 - Posted: 04.26.2016
Yuki Noguchi Hey! Wake up! Need another cup of coffee? Join the club. Apparently about a third of Americans are sleep-deprived. And their employers are probably paying for it, too, in the form of mistakes, productivity loss, accidents and increased health insurance costs. A recent Robert Wood Johnson Foundation report found a third of Americans get less sleep than the recommended seven hours. Another survey by Accountemps, an accounting services firm, put that number at nearly 75 percent in March. Bill Driscoll, Accountemps' regional president in the greater Boston area, says some sleepy accountants even admitted it caused them to make costly mistakes. "One person deleted a project that took 1,000 hours to put together," Driscoll says. "Another person missed a decimal point on an estimated payment and the client overpaid by $1 million. Oops. William David Brown, a sleep psychologist at the University of Texas Southwestern Medical School and author of Sleeping Your Way To The Top, says Americans are sacrificing more and more sleep every year. Fatigue is cumulative, he says, and missing the equivalent of one night's sleep is like having a blood alcohol concentration of about .1 — above the legal limit to drive. "About a third of your employees in any big company are coming to work with an equivalent impairment level of being intoxicated," Brown says. © 2016 npr
By Nicholas Bakalar Eating a high-fat diet may lead to daytime sleepiness, a new study concludes. Australian researchers studied 1,800 men who had filled out food-frequency questionnaires and reported on how sleepy they felt during the day. They were also electronically monitored for obstructive sleep apnea, which causes people to wake up many times during the night. After adjusting for factors that could influence sleep — smoking, alcohol intake, waist circumference, physical activity, medications, depression and others — they found that compared with those in the lowest one-quarter for fat intake, those in the highest one-quarter were 78 percent more likely to suffer daytime sleepiness and almost three times as likely to have sleep apnea. The connection of fat intake to apnea was apparent most clearly in people with a high body mass index, but the positive association of fat intake with daytime sleepiness persisted strongly in all subjects, regardless of B.M.I. Thestudy is in the journal Nutrients. “The possible mechanism could be meal timing, but we didn’t have that information,” said the lead author, Yingting Cao, a doctoral candidate at the University of Adelaide. “But we have reason to believe that circadian rhythm, hormones and diet all work together to create these effects. © 2016 The New York Times Company
Laura Sanders Away from home, people sleep with one ear open. In unfamiliar surroundings, part of the left hemisphere keeps watch while the rest of the brain is deeply asleep, scientists report April 21 in Current Biology. The results help explain why the first night in a hotel isn’t always restful. Some aquatic mammals and birds sleep with half a brain at a time, a trick called unihemispheric sleep. Scientists have believed that humans, however, did not show any such asymmetry in their slumber. Study coauthor Yuka Sasaki of Brown University in Providence, R.I., and colleagues looked for signs of asymmetry on the first night that young, healthy people came into their sleep lab. Usually, scientists toss the data from the inaugural night because the sleep is so disturbed, Sasaki says. But she and her team thought that some interesting sleep patterns might lurk within that fitful sleep. “It was a little bit of a crazy hunch,” she says, “but we did it anyway.” On the first night in a sleep lab, people with more “awake” left hemispheres took longer to fall asleep. This asymmetry was largely gone on the second night, and people fell asleep more quickly. During a deep sleep stage known as slow-wave sleep, a network of nerve cells in the left side of the brain showed less sleep-related activity than the corresponding network on the right side. Those results suggest that the left side of the brain is a lighter sleeper. “It looked like the left hemisphere and the right hemisphere did not show the same degree of sleep,” Sasaki says. This imbalance disappeared on the second night of sleep. © Society for Science & the Public 2000 - 2016