Chapter 15. Brain Asymmetry, Spatial Cognition, and Language
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By Virginia Morell When you hear a bird warbling, you probably think the crooner is a male. And chances are if you’re in the Northern Hemisphere, you would be right. But females also evolved to sing, and many still do—although generally less than the males. One reason may be that it’s more dangerous for them to sing especially when nesting, scientists report today. At least, that’s the case for female fairywrens, the most vocal of which are the most likely to have their eggs and chicks eaten. The study “provides some of the first field evidence indicating why females of so many songbird species might have lost song,” says Karan Odom, a Ph.D. candidate at the University of Maryland, Baltimore, and the lead author of a 2014 study on the evolution of birdsong. Female superb fairywrens (Malarus cyaneus)—a small Australian species—aren’t the only female songbirds that sing. In fact, females sing in 71% of songbird species, often for territorial defense. In species like the superb fairywren, some females even sing when they’re on their nests, a place where, at least theoretically, they should pipe down so as not to attract predators. Rodents, birds, cats, and foxes have all been seen preying on the fairywrens’ nests. “People had observed [this singing in the nest behavior], but they hadn’t investigated it,” says Sonia Kleindorfer, a behavioral ecologist at Flinders University in Adelaide, Australia. “It struck me as odd, and very risky.” © 2016 American Association for the Advancement of Science
By Tania Rabesandratana Here’s one trick to make yourself feel happier: Listen to your own voice—digitally manipulated to make it sound cheery. That’s one potential application of a new study, in which researchers modified the speech of volunteers as they read a short story by Japanese writer Haruki Murakami. The team then altered the voice’s pitch, among other features, to make it sound happy, sad, or fearful. (Compare this normal voice with the same voice modified to sound afraid.) Listening to their own modified voices in real time through a headset, only 16 of 109 participants detected some kind of manipulation. The rest took the voice’s emotion as their own, feeling sad or happy themselves. (The result was less clear for fear.) The researchers suggest that emotions expressed through our voices are part of an ancient, unconscious primate communication system, whereas we have more conscious control over the words we utter. The voice manipulation software is available online, so anyone can experiment with it. The scientists speculate that emotion manipulation could help treat psychiatric disorders like depression. It could also change the mood of online meetings or gaming, they say, or even lend more emotional impact to singing performances. © 2016 American Association for the Advancement of Science
AUDIE CORNISH, HOST: It's unusual for an NFL player - a current player - to criticize the league, especially its handling of controversial issues like concussions or domestic violence, but author Johnny Anonymous has done just that. He's an offensive lineman who's written a book under that pseudonym. It's called "NFL Confidential." In it, he details his 2014 season, including training camp and his big break after a starting player gets injured. He's worried about being fired, so we've masked his voice. First, Johnny Anonymous says getting hurt is always on the mind of the player. ANONYMOUS: It's absolutely constant. The NFL's the only league, the only job you'll find in the world where we have a 100 percent injury rate. CORNISH: So walk us through the questions that come to mind for a player when they first hear that, you know, sickening sound and they're lying there on the field. What are you thinking? ANONYMOUS: For some guys, it's fear, which is why you'll see them kicking and screaming and crying, and some guys it's shock. I know for most of us - and probably all of us - the first thing you think is, I'm done; that's it. You think the injury's going to take the game away from you. CORNISH: So in a way, you know, this is how it happens, right, this discussion of, like, why do people take all the painkillers, you know, like, why do people defy doctors? ANONYMOUS: You have to. It's the only way you make it through. I can tell you right now, honestly, that if I am playing a game, I cannot complete that game without painkillers. I will not be an effective player. © 2016 npr
Keyword: Brain Injury/Concussion
Link ID: 21766 - Posted: 01.09.2016
By Josh Izaac Helmets can reduce the risk of traumatic brain injury by almost 20%. But what if we take so many risks when wearing them that we lose the protective edge they provide? This could be the case, according to a study published this week. Researchers observed 80 cyclists under the guise of an “eye-tracking experiment,” pretending to track their eye-motion via a head-mounted camera as the participants inflated a virtual balloon. For some of the participants, the “eye-tracking devices” were mounted on helmets, while others just wore baseball caps, as can be seen in the picture of the equipment above. The further they inflated the balloon without it popping, the higher their reward and their risk-taking score. Participants wearing helmets inflated their balloons on average 30% more than those who wore caps, the team reports in Psychological Science. The finding could affect how we approach safety design and training, the authors say, as increased risk-taking behavior when using safety equipment might counteract the perceived benefit of the equipment. But what causes this effect in the first place? The underlying mechanism might be related to the concept of “social priming,” where people’s actions towards others are altered subconsciously due to exposure to particular words, cues, objects, or symbols. Importantly, this is the first time social priming has been shown to change people’s behaviour even when they are not interacting with others, providing potential new insights into human behavior. So, next time you’re out riding with a helmet, think twice before attempting that wheelie. © 2016 American Association for the Advancement of Science
Keyword: Brain Injury/Concussion
Link ID: 21765 - Posted: 01.09.2016
Bruce Bower Youngsters befuddled by printed squiggles on the pages of a storybook nonetheless understand that a written word, unlike a drawing, stands for a specific spoken word, say psychologist Rebecca Treiman of Washington University in St. Louis and her colleagues. Children as young as 3 can be tested for a budding understanding of writing’s symbolic meaning, the researchers conclude January 6 in Child Development. “Our results show that young children have surprisingly advanced knowledge about the fundamental properties of writing,” Treiman says. “This knowledge isn’t explicitly taught to children but probably gained through early exposure to print from sources such as books and computers.” Researchers and theorists have previously proposed that children who cannot yet read don’t realize that a written word corresponds to a particular spoken word. Studies have found, for instance, that nonliterate 3- to 5-year-olds often assign different meanings to the same word, such as girl, depending on whether that word appears under a picture of a girl or a cup. Treiman’s investigation “is the first to show that kids as young as 3 have the insight that print stands for something beyond what’s scripted on the page,” says psychologist Kathy Hirsh-Pasek of Temple University in Philadelphia. Preschoolers who are regularly read to have an advantage in learning that written words have specific meanings, suspects psychologist Roberta Golinkoff of the University of Delaware in Newark. © Society for Science & the Public 2000 - 2015.
A 25-year-old former college football player showed signs of a type of brain degeneration from repeated trauma, say researchers who described the autopsy-confirmed case. Chronic traumatic encephalopathy (CTE) is a neurodegenerative disorder associated with repetitive head impacts. Symptoms may include memory loss, impaired judgment, depression and progressive dementia. CTE can only be diagnosed after death by examining the brain. Monday's issue of JAMA Neurology includes a letter describing CTE in a 25-year-old man born with a heart valve disorder. He died of cardiac arrest secondary to a heart infection after playing football for 16 years and experiencing an estimated more than 10 concussions while playing. Dr. Ann McKee and Dr. Jesse Mez of Boston University School of Medicine ran neuropsychological tests on the man when he showed symptoms a year before his death, and then conducted an autopsy, reviewed his medical records and interviewed family members. "Focal lesions of CTE have been found in athletes as young as 17 years; however, widespread CTE pathology, as found in this case, is unusual in such a young football player," they wrote. To their knowledge, it's the first such case to include neuropsychological testing to document the type of cognitive issues with CTE. In this case, the athlete started playing football when he was six, including three years of college football as a defensive linebacker. His first concussion occurred at age eight. ©2015 CBC/Radio-Canada.
Keyword: Brain Injury/Concussion
Link ID: 21750 - Posted: 01.05.2016
By KEN BELSON When St. Louis Rams quarterback Case Keenum sustained a concussion in a game in Baltimore last month, commentators focused on how he wobbled as he got up and questioned why he was not taken out of the game. Few mentioned that he had slammed his head on the turf. In the rush to reduce head trauma in sports, doctors, researchers, leagues and equipment makers have looked at everything from improving helmets to teaching safer tackling techniques. But one little-explored cause of concussions is the field beneath the feet of the millions of athletes who play football, lacrosse, soccer and other sports. A new report compiled by the Concussion Legacy Foundation called attention to the link between head injuries and poorly maintained fields, especially the growing number of those made of synthetic turf. The foundation urged groundskeepers, athletic directors and sports associations to treat their fields as seriously as other protective sports equipment. “We have no national conversation on the technology underneath an athlete’s feet,” the authors wrote in their report, the Role of Synthetic Turf in Concussion. “Helmet technology is an area of great attention and investment, and surfaces deserve the same attention.” The report, which is based on more than a dozen academic studies, cites research that shows that 15.5 percent of concussions in high school sports occur when players hit their head on a playing surface. Another study found that 10 percent of concussions sustained by high school and college football players came after players hit their head on a field. In the N.F.L., about one in seven concussions occurs when a player’s head strikes a synthetic or grass field. © 2015 The New York Times Company
Keyword: Brain Injury/Concussion
Link ID: 21737 - Posted: 12.30.2015
by Sarah Zielinski When you get a phone call or a text from a friend or acquaintance, how fast you respond — or whether you even bother to pick up your phone — often depends on the quality of the relationship you have with that person. If it’s your best friend or mom, you probably pick up right away. If it’s that annoying coworker contacting you on Sunday morning, you might ignore it. Ring-tailed lemurs, it seems, are even pickier in who they choose to respond to. They only respond to calls from close buddies, a new study finds. These aren’t phone calls but contact calls. Ring-tailed lemurs live in female-dominated groups of 11 to 16, and up to 25, animals, and when the group is on the move, it’s common for one member to yell out a “meow!” and for other members to “meow!” back. A lemur may also make the call if it gets lost. The calls serve to keep the group together. The main way ring-tailed lemurs (and many other primates) build friendships, though, is through grooming. Grooming helps maintain health and hygiene and, more importantly, bonds between members. It’s a time-consuming endeavor, and animals have to be picky about who they bother to groom. Ipek Kulahci and colleagues at Princeton University wanted to see if there was a link between relationships built through grooming and vocal exchanges among ring-tailed lemurs. Contact calls don’t require nearly as much time or effort as grooming sessions, so it is possible that animals could be less discriminating when they respond to calls. But, the researchers reasoned, if the vocalizations were a way of maintaining the relationships built through painstaking grooming sessions, then the lemurs would be as picky in their responses as in their grooming partners. © Society for Science & the Public 2000 - 2015.
By KEN BELSON Researchers at several universities and research institutes were awarded almost $16 million Tuesday to find a way to diagnose, while victims are alive, chronic traumatic encephalopathy, a degenerative brain disease linked to repeated head hits in contact sports. The National Institutes of Health and the National Institute of Neurological Disorders and Stroke issued the seven-year grant as part of a long-term study of brain disease in former N.F.L. and college football players, many of whom sustained multiple concussions on the field. Despite the implications that the research may have on football players and the N.F.L., no league money will be used to help pay for the grant. For years, researchers have been able to diagnose C.T.E. only by examining the brains of players who died and whose families agreed to donate the organ, a limitation that has slowed efforts to determine who is susceptible to having the disease. The new study, considered among the most ambitious in the field of sports-related brain injury, aims to develop ways to spot the disease in the living and figure out why certain players get it and others do not. A more comprehensive understanding of the disease, the researchers said, may lead to ways to prevent it. “There are so many critical unanswered questions about C.T.E.,” Dr. Robert Stern, the lead principal investigator and a professor at Boston University School of Medicine, said in a statement. “We are optimistic that this project will lead to many of these answers, by developing accurate methods of detecting and diagnosing C.T.E. during life, and by examining genetic and other risk factors for this disease.” © 2015 The New York Times Company
Keyword: Brain Injury/Concussion
Link ID: 21723 - Posted: 12.24.2015
Scientists hunting for a drug that speeds stroke recovery might find one in the bedside cabinets of millions of Americans. Mice treated with small doses of the sleeping pill Ambien recovered more quickly from strokes than those given a placebo. Ambien is the best-known incarnation of the drug zolpidem, which was prescribed 40 million times in the US in 2011. The researchers say that the finding should be replicated by other labs before proceeding with clinical trials, but it’s an intriguing result for a problem in desperate need of solutions. Strokes cut off the blood supply to part of the brain, leading to the death of oxygen-starved tissue. Some tissue repair can take place in the months afterwards, but most people never fully recover. Although physical therapy can help, there are no drugs that increase the amount of brain tissue repaired. “There are various natural mechanisms that promote a degree of normal recovery in animals and people, but it’s limited”, says Gary Steinberg of Stanford University School of Medicine, who was lead author of the study. One such mechanism may be an increase in signalling by the GABA neurotransmitter in parts of the brain that are able to rewire themselves. Because Ambien acts on GABA receptors, Steinberg and his team wondered whether they could use it to hack this mechanism to improve recovery. © Copyright Reed Business Information Ltd.
By C. CLAIBORNE RAY Q. We know that aquatic mammals communicate with one another, but what about fish? A. Fish have long been known to communicate by several silent mechanisms, but more recently researchers have found evidence that some species also use sound. It is well known that fish communicate by gesture and motion, as in the highly regimented synchronized swimming of schools of fish. Some species use electrical pulses as signals, and some use bioluminescence, like that of the firefly. Some kinds of fish also release chemicals that can be sensed by smell or taste. In 2011, a scientist in New Zealand suggested that what might be called fish vocalization has a role, at least in some ocean fish. In the widely publicized work, done for his doctoral thesis at the University of Auckland, Shahriman Ghazali recorded reef fish in the wild and in captivity, and found two dominant vocalizations, the croak and the purr, in choruses that lasted up to three hours, as well as a previously undescribed popping sound. The sounds of one species recorded in captivity — the bigeye, or Pempheris adspersa — carried 100 feet or more, and the researcher suggested it could be used to keep a group of fish together during nocturnal foraging. Another species, the bluefin gurnard, or Chelidonichthys kumu, was also very noisy, he found. “Vocalization” is a bit of a misnomer, as the sounds these fish make are produced by contracting and vibrating the swim bladder, not by using the mouth. © 2015 The New York Times Company
By SINDYA N. BHANOO Moderate levels of exercise may increase the brain’s flexibility and improve learning, a new study suggests. The visual cortex, the part of the brain that processes visual information, loses the ability to “rewire” itself with age, making it more difficult for adults to recover from injuries and illness, said Claudia Lunghi, a neuroscientist at the University of Pisa and one of the study’s authors. In a study in the journal Current Biology, she and her colleagues asked 20 adults to watch a movie with one eye patched while relaxing in a chair. Later, the participants exercised on a stationary bike for 10-minute intervals while watching a movie. When one eye is patched, the visual cortex compensates for the limited input by increasing its activity level. Dr. Lunghi and her colleagues tested the imbalance in strength between the participants’ eyes after the movie — a measure of changeability in the visual cortex. © 2015 The New York Times Company
Link ID: 21681 - Posted: 12.08.2015
Helen Thompson Just after dawn, barbershop quartets of male howler monkeys echo over the canopy of Mexico’s forests. Jake Dunn remembers them well from his early fieldwork in Veracruz. “Most people who don’t know what they’re listening to assume it’s a jaguar,” says Dunn, a primatologist at the University of Cambridge. The calls serve as a warning to male competitors and an alluring pickup line for females. While studying primates in Mexico, Dunn heard drastic differences between resident howler monkeys. He and his colleagues decided to pin down the origin and evolution of this well-known variation among species. After reading a 1949 paper that classified howlers based on a vocal tract bone called the hyoid, Dunn paired up with Lauren Halenar of the American Museum of Natural History in New York City, who was studying the hyoid’s role in howler biology. Scouring collections at museums and zoos in the United States and Europe, the team used laser scanners to create 3-D models of hyoids from nine howler species. The work required a lot of digging through cupboards for skeletons. “Some of these specimens are hundreds of years old,” says Dunn, who recalls imagining “the early naturalists hunting these animals and bringing back the collections.” Real pay dirt came from the National Museums of Scotland, which had preserved the remains of two howlers that had died of natural causes in zoos. CT and MRI scans of the two specimens provided a rare peek at the howler vocal system’s layout. © Society for Science & the Public 2000 - 2015.
By Karen Russell In late October, when the Apple TV was relaunched, Bandit’s Shark Showdown was among the first apps designed for the platform. The game stars a young dolphin with anime-huge eyes, who battles hammerhead sharks with bolts of ruby light. There is a thrilling realism to the undulance of the sea: each movement a player makes in its midnight-blue canyons unleashes a web of fluming consequences. Bandit’s tail is whiplash-fast, and the sharks’ shadows glide smoothly over rocks. Every shark, fish, and dolphin is rigged with an invisible skeleton, their cartoonish looks belied by the programming that drives them—coding deeply informed by the neurobiology of action. The game’s design seems suspiciously sophisticated when compared with that of apps like Candy Crush Soda Saga and Dude Perfect 2. Bandit’s Shark Showdown’s creators, Omar Ahmad, Kat McNally, and Promit Roy, work for the Johns Hopkins School of Medicine, and made the game in conjunction with a neuroscientist and neurologist, John Krakauer, who is trying to radically change the way we approach stroke rehabilitation. Ahmad told me that their group has two ambitions: to create a successful commercial game and to build “artistic technologies to help heal John’s patients.” A sister version of the game is currently being played by stroke patients with impaired arms. Using a robotic sling, patients learn to sync the movements of their arms to the leaping, diving dolphin; that motoric empathy, Krakauer hopes, will keep patients engaged in the immersive world of the game for hours, contracting their real muscles to move the virtual dolphin.
Angus Chen English bursts with consonants. We have words that string one after another, like angst, diphthong and catchphrase. But other languages keep more vowels and open sounds. And that variability might be because they evolved in different habitats. Consonant-heavy syllables don't carry very well in places like windy mountain ranges or dense rainforests, researchers say. "If you have a lot of tree cover, for example, [sound] will reflect off the surface of leaves and trunks. That will break up the coherence of the transmitted sound," says Ian Maddieson, a linguist at the University of New Mexico. That can be a real problem for complicated consonant-rich sounds like "spl" in "splice" because of the series of high-frequency noises. In this case, there's a hiss, a sudden stop and then a pop. Where a simple, steady vowel sound like "e" or "a" can cut through thick foliage or the cacophony of wildlife, these consonant-heavy sounds tend to get scrambled. Hot climates might wreck a word's coherence as well, since sunny days create pockets of warm air that can punch into a sound wave. "You disrupt the way it was originally produced, and it becomes much harder to recognize what sound it was," Maddieson says. "In a more open, temperate landscape, prairies in the Midwest of the United States [or in Georgia] for example, you wouldn't have that. So the sound would be transmitted with fewer modifications." © 2015 npr
Paul Ibbotson and Michael Tomasello The natural world is full of wondrous adaptations such as camouflage, migration and echolocation. In one sense, the quintessentially human ability to use language is no more remarkable than these other talents. However, unlike these other adaptations, language seems to have evolved just once, in one out of 8.7 million species on earth today. The hunt is on to explain the foundations of this ability and what makes us different from other animals. The intellectual most closely associated with trying to pin down that capacity is Noam Chomsky. He proposed a universal grammatical blueprint that was unique to humans. This blueprint operated like a computer program. Instead of running Windows or Excel, this program performed “operations” on language – any language. Regardless of which of the 6000+ human languages that this code could be exposed to, it would guide the learner to the correct adult grammar. It was a bold claim: despite the surface variations we hear between Swahili, Japanese and Latin, they are all run on the same piece of underlying software. As ever, remarkable claims require remarkable evidence, and in the 50 years since some of these ideas were laid out, history has not been kind. First, it turned out that it is really difficult to state what is “in” universal grammar in a way that does justice to the sheer diversity of human languages. Second, it looks as if kids don’t learn language in the way predicted by a universal grammar; rather, they start with small pockets of reliable patterns in the language they hear, such as Where’s the X?, I wanna X, More X, It’s a X, I’m X-ing it, Put X here, Mommy’s X-ing it, Let’s X it, Throw X, X gone, I X-ed it, Sit on the X, Open X, X here, There’s a X, X broken … and gradually build their grammar on these patterns, from the “bottom up”. © 2015 Guardian News and Media Limited
Link ID: 21607 - Posted: 11.06.2015
Nicole Fisher , We know that the brain is neuroplastic — adapts to changes in behavior, environment, thinking and emotions — and may even rewire itself in certain ways. Life experience also teaches us that the tongue is a learning tool that shapes our brain. During early development, babies test everything by placing it in their mouths. As children age they stick out their tongues when concentrating on tasks such as drawing. Even as adults we let our tongue tell us about the world around us through eating, drinking and kissing. During basketball games, some players stick out their tongues while shooting. Now, knowing that there is such a rich nerve connection to the brain, scientists and doctors are turning to the tongue as a way to possibly stimulate the brain for neural retraining and rehabilitation after traumatic injuries or disease. The team at Helius Medical Technologies believe combining physical therapy with stimulation of the tongue may improve impairment of brain function and associated symptoms of injury. “We have already seen that stimulation of various nerves can improve symptoms of a range of neurological diseases. However, we believe the tongue is a much more elegant and direct pathway for stimulating brain structures and inducing neuroplasticity. We are focused on investigating the tongue as a gateway to the brain to hopefully ease the disease of brain injury,” said Dr. Jonathan Sackier, CMO at Helius. It has been argued by some that the era of small molecule is gone. Instead, recognition that the entire body is a closed electrical circuit, is leading to new therapeutic modalities that are known in certain circles as “electroceuticals.”
Looking at brain tissue from mice, monkeys and humans, scientists have found that a molecule known as growth and differentiation factor 10 (GDF10) is a key player in repair mechanisms following stroke. The findings suggest that GDF10 may be a potential therapy for recovery after stroke. The study, published in Nature Neuroscience, was supported by the National Institute of Neurological Disorders and Stroke (NINDS), part of the National Institutes of Health. “These findings help to elucidate the mechanisms of repair following stroke. Identifying this key protein further advances our knowledge of how the brain heals itself from the devastating effects of stroke, and may help to develop new therapeutic strategies to promote recovery,” said Francesca Bosetti, Ph.D., stroke program director at NINDS. Stroke can occur when a brain blood vessel becomes blocked, preventing nearby tissue from getting essential nutrients. When brain tissue is deprived of oxygen and nutrients, it begins to die. Once this occurs, repair mechanisms, such as axonal sprouting, are activated as the brain attempts to overcome the damage. During axonal sprouting, healthy neurons send out new projections (“sprouts”) that re-establish some of the connections lost or damaged during the stroke and form new ones, resulting in partial recovery. Before this study, it was unknown what triggered axonal sprouting. Previous studies suggested that GDF10 was involved in the early stages of axonal sprouting, but its exact role in the process was unclear. S. Thomas Carmichael, M.D., Ph.D., and his colleagues at the David Geffen School of Medicine at the University of California Los Angeles took a closer look at GDF10 to identify how it may contribute to axonal sprouting.
By Bob Grant Scientists delving into the neurological underpinnings of traumatic brain injuries (TBI) are finding that there may be crucial differences in the long-term effects of the events that depend not only on the insult, but also on the victim. “No two brain injuries are identical,” University of Pennsylvania neuroscientist Akiva Cohen said during a press conference held at the Society for Neuroscience (SfN) annual meeting in Chicago on Monday (October 19). “Brain injury, like many pathologies these days, constitutes a spectrum.” In addition to a severity spectrum that spans mild to severe, brain injuries may differ in terms of how male and female animals respond to them, according to Ramesh Raghupathi, a neurobiologist at Drexel University. Raghupathi and his colleagues have found that young male mice suffer more depressive behaviors than female mice at both four and eight weeks after mild TBI, and females display more headache-like symptoms after similar insults, which can include concussion. “All of these animals at these times after injury are cognitively normal,” Raghupathi told reporters. “And they do not have any movement problems.” Raghupathi and his colleagues also found molecular differences that may underlie the sex differences in TBI response that they observed. “In the male mice,” he said, “there is a dramatic difference in dopamine transmission” compared to the uninjured mice.” Researchers have previously linked impaired dopamine signaling to depression. Raghupathi’s team tested for the lingering effects of TBI in mice by subjecting the animals to certain swimming tests—which are accepted as proxies for depression—and by using a thin filament to touch the faces of the rodents and recording their sensitivity as a measure of headache-like behaviors.
By Jonathan Webb Science reporter, BBC News Crocodiles can sleep with one eye open, according to a study from Australia. In doing so they join a list of animals with this ability, which includes some birds, dolphins and other reptiles. Writing in the Journal of Experimental Biology, the researchers say the crocs are probably sleeping with one brain hemisphere at a time, leaving one half of the brain active and on the lookout. Consistent with this idea, the crocs in the study were more likely to leave one eye open in the presence of a human. They also kept that single eye trained directly on the interloper, said senior author John Lesku. "They definitely monitored the human when they were in the room. But even after the human left the room, the animal still kept its open eye… directed towards the location where the human had been - suggesting that they were keeping an eye out for potential threats." The experiments were done in an aquarium lined with infrared cameras, to monitor juvenile crocodiles day and night. "These animals are not particularly amenable to handling; they are a little snippy. So we had to limit all of our work to juvenile crocodiles, about 40-50cm long," said Dr Lesku, from La Trobe University in Melbourne. As well as placing a human in the room for certain periods, the team tested the effect of having other young crocs around. Sure enough, these also tended to attract the gaze of any reptiles dozing with only one eye. This matches what is known of "unihemispheric sleep" in aquatic mammals, such as walruses and dolphins, which seem to use one eye to make sure they stick together in a group. © 2015 BBC.