Chapter 6. Hearing, Balance, Taste, and Smell
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By Tina Hesman Saey When a cold takes away a person’s sense of smell, part of the brain that helps link odors with memory, emotion and reward works overtime in preparation for the return of air flow. The way smell rebounds from a period of diminished sensory input distinguishes it from the other senses, researchers at the Northwestern University School of Medicine in Chicago report online August 12 in Nature Neuroscience. Other senses tend to back off when their functions are restricted. When a person wears a patch over one eye, for example, the part of the brain devoted to processing information from that eye weakens while the part linked to the other eye grows stronger. The same is true for hearing and touch, such as when a person goes deaf in one ear or loses a finger. To find out what happens to the olfactory system — the part of the brain that processes scents — when it’s completely odor deprived, Northwestern neuroscientist Joanna Keng Nei Wu and her colleagues set up a scent-free zone in a hospital’s research wing. Volunteers had to give up scented toiletries and spend a week with cotton stuffed up their nostrils to seal their noses off from the outside world. The researchers even took away the volunteers’ toothpaste, forcing them to brush with baking soda instead. Despite the hardships, it wasn’t difficult to find willing volunteers, Wu says. “We had a lot of medical students who wanted us to lock them up in the hospital for a week so they could study.” © Society for Science & the Public 2000 - 2012
Keyword: Chemical Senses (Smell & Taste)
Link ID: 17158 - Posted: 08.14.2012
by Nicholas St. Fleur With their trumpet-like calls, elephants may seem like some of the loudest animals on Earth. But we can't hear most of the sounds they make. The creatures produce low-frequency noises between 1 to 20 Hertz, known as infrasounds, that help them keep in touch over distances as large as 10 kilometers. A new study reveals for the first time how elephants produce these low notes. Scientists first discovered that elephants made infrasounds in the 1980s. The head female in a herd may produce the noises to guide her group's movements, whereas a male who’s in a mating state called musth might use the calls to thwart competition from other males. Mother elephants even rely on infrasounds to keep tabs on a separated calf, exchanging "I'm here" calls with the wayward offspring in a fashion similar to a game of Marco Polo. These noises, which fall below the hearing range for humans, are often accompanied by strong rumbles with slightly higher frequencies that people can hear. By recording the rumbles and then speeding up the playback, the scientists can increase the frequency of the infrasounds, making them audible. Good vibrations. The vocal folds of the excised larynx vibrating according to the myoelastic-aerodynamic method. Researchers have speculated that the noises come from vibrations in the vocal folds of the elephant larynx. This could happen in two ways. In the first, called active muscular contraction (AMC), neural signals cause the muscles in the larynx to contract in a constant rhythm. Cats do this when they purr. The second possibility is known as the myoelastic-aerodynamic (MEAD) method, and it occurs when air flows through the vocal folds causing them to vibrate—this also happens when humans talk. © 2010 American Association for the Advancement of Science
Published by scicurious under Behavioral Neuro Imagine for a minute. You're in a coffeeshop, or a bar, or at a swanky cocktail party (whichever you prefer). There are people around, chatting nearby. But you're speaking to the person directly across from you. Somehow, you can pick their voice out of the chatter and attend to what they are saying, even though the conversations around you might be just as loud or louder (especially in a bar!) than the one you're interested in. Have you ever wondered how you do that? I know I have. It's kind of a mind-boggling problem (and is, in fact, called the Cocktail party problem), trying to separate out speech, and make sense of it, in comparison to all the noise. And it's not just something to think about for us humans. Voice recognition technology and recording wrestles with this all the time: how to pick out the voice from the crowd? As it turns out, it's all about attention, and how that attention can change your brain. The authors of this study were interested in what happens in the brain when someone tries to pick out a single speaker in a room full of people. To look at this, they actually used electrodes implanted subdurally (beneath the tough dura mater on the outside of the brain) in three human patients. Three is a really small number, but they had to use patients who were receiving this electrode implant clinically, in this case for treatment of epilepsy, and who were known to have normal hearing and language skills. Copyright © 2012
by Nicholas St. Fleur A house fly couple settles down on the ceiling of a manure-filled cowshed for a romantic night of courtship and copulation. Unbeknownst to the infatuated insects, their antics have attracted the acute ears of a lurking Natterer's bat. But this eavesdropper is no pervert—he's a predator set on a two-for-one dinner special. As a new study reveals, the hungry bat swoops in on the unsuspecting flies, guided by the sound of their precoital "clicks." Previous studies of freshwater amphipods, water striders, and locusts have shown that mating can make animals more vulnerable to predators, but these studies did not determine why. A team from the Max Planck Institute for Ornithology in Germany, led by the late Björn Siemers, found that the bat-fly interactions in the cowshed provided clues for understanding what tips off a predator to a mating couple. The researchers observed a teenage horror film-like scene as Natterer's bats (Myotis nattereri)preyed on mating house flies (Musca domestica). Bats find prey primarily through two methods: echolocation and passive acoustics. For most bats, echolocation is the go-to tracking tool. They send out a series of high frequency calls and listen for the echoes produced when the waves hit something. The researchers found that by using echolocation, bats could easily find and catch house flies midflight, yet they had difficulty hunting stationary house flies. © 2010 American Association for the Advancement of Science
by Gisela Telis During mating season, a moss needs a little help from its friends—and it uses smell to recruit them. A new study has found that mosses, which were long thought to require only water or wind to reproduce, release an aroma that entices tiny animals such as mites and little bugs called springtails to help fertilize the plants. The discovery challenges current ideas about plant evolution, but experts say it raises more questions than it answers. For mosses, sex can be tricky. They can reproduce asexually, or they can develop male and female sex organs and wait for their fragile sperm to travel from one to the other. If the latter occurs, they rely on the elements—wind or splashing rain—to help with transport. In 2006, researchers discovered a third means of delivery. They found that tiny arthropods, a group of creepy-crawlies that includes mites and springtails, seemed to help disperse moss sperm. But the study didn't pinpoint how they did it or whether this kind of fertilization was critical to the moss life cycle. In hopes of answering those lingering questions, biologist Sarah Eppley of Portland State University in Oregon and colleagues gathered and grew moss samples from local forests and tested reproductive outcomes with and without rain and springtails. They found that water alone and springtails alone were equally effective at fertilizing mosses, but putting the two together made the mosses more than twice as successful at reproducing. © 2010 American Association for the Advancement of Science
By Victoria Gill BBC Nature Seabirds are able to pick out their relatives from smell alone, according to scientists. In a "recognition test", European storm petrels chose to avoid the scent of a relative in favour of approaching the smell of an unrelated bird. The researchers think this behaviour prevents the birds from "accidentally inbreeding". The study is the first evidence that birds are able to sniff out a suitable mate. It is published in the journal Animal Behaviour. Lead researcher Francesco Bonadonna, from the Centre of Functional and Evolutionary Ecology in Montpellier, France, told BBC Nature that the birds used smell to recognise and communicate their "genetic compatibility". Sniffing out a genetically suitable mate is a well-known phenomenon in mammals. But until recently, scientists thought that birds relied on vision and sound when choosing a partner. According to Dr Bonadonna, the fact that they use odours explains how these birds manage to return to their family colony to breed and avoid mating with a relative. European storm petrels remain in the colony they are born in throughout their life, so this site is also home to several of their family members. BBC © 2012
By WILLIAM J. BROAD Scientists have long known that man-made, underwater noises — from engines, sonars, weapons testing, and such industrial tools as air guns used in oil and gas exploration — are deafening whales and other sea mammals. The Navy estimates that loud booms from just its underwater listening devices, mainly sonar, result in temporary or permanent hearing loss for more than a quarter-million sea creatures every year, a number that is rising. Now, scientists have discovered that whales can decrease the sensitivity of their hearing to protect their ears from loud noise. Humans tend to do this with index fingers; scientists haven’t pinpointed how whales do it, but they have seen the first evidence of the behavior. “It’s equivalent to plugging your ears when a jet flies over,” said Paul E. Nachtigall, a marine biologist at the University of Hawaii who led the discovery team. “It’s like a volume control.” The finding, while preliminary, is already raising hopes for the development of warning signals that would alert whales, dolphins and other sea mammals to auditory danger. Peter Madsen, a professor of marine biology at Aarhus University in Denmark, said he applauded the Hawaiian team for its “elegant study” and the promise of innovative ways of “getting at some of the noise problems.” But he cautioned against letting the discovery slow global efforts to reduce the oceanic roar, which would aid the beleaguered sea mammals more directly. © 2012 The New York Times Company
People who are born deaf process the sense of touch differently than people who are born with normal hearing, according to research funding by the National Institutes of Health. The finding reveals how the early loss of a sense — in this case hearing — affects brain development. It adds to a growing list of discoveries that confirm the impact of experiences and outside influences in molding the developing brain. The study is published in the July 11 online issue of The Journal of Neuroscience. The researchers, Christina M. Karns, Ph.D., a postdoctoral research associate in the Brain Development Lab at the University of Oregon, Eugene, and her colleagues, show that deaf people use the auditory cortex to process touch stimuli and visual stimuli to a much greater degree than occurs in hearing people. The finding suggests that since the developing auditory cortex of profoundly deaf people is not exposed to sound stimuli, it adapts and takes on additional sensory processing tasks. "This research shows how the brain is capable of rewiring in dramatic ways," said James F. Battey, Jr., M.D., Ph.D., director of the NIDCD. "This will be of great interest to other researchers who are studying multisensory processing in the brain." Previous research, including studies performed by the lab director, Helen Neville Ph.D., has shown that people who are born deaf are better at processing peripheral vision and motion. Deaf people may process vision using many different brain regions, especially auditory areas, including the primary auditory cortex. However, no one has tackled whether vision and touch together are processed differently in deaf people, primarily because in experimental settings, it is more difficult to produce the kind of precise tactile stimuli needed to answer this question.
by Elizabeth Preston It's 20 million years ago in the forests of Argentina, and Homunculus patagonicus is on the move. The monkey travels quickly, swinging between tree branches as it goes. Scientists have a good idea of how Homunculus got around thanks to a new fossil analysis of its ear canals and those of 15 other ancient primates. These previously hidden passages reveal some surprises about the locomotion of extinct primates—including hints that our own ancestors spent their lives moving at a higher velocity than today's apes. Wherever skeletons of ancient primates exist, anthropologists have minutely analyzed arm, leg, and foot bones to learn about the animals' locomotion. Some of these primates seem to have bodies built for leaping. Others look like they moved more deliberately. But in species such as H. patagonicus, there's hardly anything to go on aside from skulls. That's where the inner ear canals come in. "The semicircular canals function essentially as angular accelerometers for the head," helping an animal keep its balance while its head jerks around, says Timothy Ryan, an anthropologist at Pennsylvania State University, University Park. In the new study, he and colleagues used computed tomography scans to peer inside the skulls of 16 extinct primates, spanning 35 million years of evolution, and reconstruct the architecture of their inner ears. © 2010 American Association for the Advancement of Science
Children exposed to HIV in the womb may be more likely to experience hearing loss by age 16 than are their unexposed peers, according to scientists in a National Institutes of Health research network. The researchers estimated that hearing loss affects 9 to 15 percent of HIV-infected children and 5 to 8 percent of children who did not have HIV at birth but whose mothers had HIV infection during pregnancy. Study participants ranged from 7 to 16 years old. The researchers defined hearing loss as the level at which sounds could be detected, when averaged over four frequencies important for speech understanding (500, 1000, 2000, and 4000 Hertz), that was 20 decibels or higher than the normal hearing level for adolescents or young adults in either ear. “Children exposed to HIV before birth are at higher risk for hearing difficulty, and it's important for them—and the health providers who care for them—to be aware of this,” said George K. Siberry, M.D., of the Pediatric, Adolescent, and Maternal AIDS Branch of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), the NIH institute that leads the research network. Compared to national averages for other children their age, children with HIV infection were about 200 to 300 percent more likely to have a hearing loss. Children whose mothers had HIV during pregnancy but who themselves were born without HIV were 20 percent more likely than to have hearing loss. The study was published online in The Pediatric Infectious Disease Journal.
By Scicurious Before I started college, there was a sudden rage amongst my male friends. A rage for one specific thing. Not phones or computers or cars or clothes. Nope. It was for a guitar. Most of the guys I knew, in the year or two before college, suddenly became obsessed with the guitar, picking out melodies, trying to match still changing warbling voices to a hopefully tuned instrument. I couldn’t figure it out. What was up with the guitar obsession?! Some of these people were people who never had displayed a musical bent their entire lives, and here they were, sitting experimentally on the benches outside my school with guitars in hand. Finally, I asked my brother (who also, of course, had taken up the guitar), why every guy seemed to want to play the guitar. Why not the cello or the piano or the trombone or the kazoo? My brother rolled his eyes at my denseness. “For the GIRLS, of course” (And yes, specifically, they ALL wanted to play this song. I would hypothesize that about 80% of the men I know can pick out this song on the guitar. Considering that a substantial portion of the female populace does indeed have brown eyes, I realize the efficiency of this method, but for those of us with non-brown eyes, this song is IRRITATING BEYOND BELIEF. This has been a public service announcement.) © 2012 Scientific American
By Susan Milius ALBUQUERQUE — Unbeknownst to humans, peacocks may be having infrasonic conversations. New recordings reveal that males showing off their feathers make deep rumbling sounds that are too low pitched for humans to hear. Other peacocks hear it though, Angela Freeman reported June 13 at the annual meeting of the Animal Behavior Society. When she played recordings of the newly discovered sound to peafowl, females looked alert and males were likely to shriek out a (human-audible) call. Peacocks are thus the first birds known to make and perceive noises below human hearing, Freeman said. ”Really exciting,” said Roslyn Dakin of Queen’s University in Kingston, Canada, who studies the visual allure of peacock courtship. If peacocks can rumble, she suspects that other birds may be able to, too. “I don’t think this is a weird case,” she said. Such infrasound, or noise below 20 hertz, extends below the limit of human hearing. Biologists watched creatures such as elephants for centuries before recording technology uncovered the infrasound side of those animal conversations. But making infrasound doesn’t always mean communicating with it. Recordings have picked up infrasound from another bird, the capercaillie, but playing back the sounds to those birds has so far revealed no sign that they hear or care about their own infrasound. Freeman, an animal behaviorist at the University of Manitoba, was inspired to make detailed recordings of male peacocks by her coauthor’s impression that their fanned-out feather display curved slightly forward like a shallow satellite dish. © Society for Science & the Public 2000 - 2012
By Janet Raloff By baffling the brain, saccharin and other sugar-free sweeteners — key weapons in the war on obesity — may paradoxically foster overeating. At some level, the brain can sense a difference between sugar and no-calorie sweeteners, several studies have demonstrated. Using brain imaging, San Diego researchers now show that the brain processes sweet flavors differently depending on whether a person regularly consumes diet soft drinks. “This idea that there could be fundamental differences in how people respond to sweet tastes based on their experience with diet sodas is not something that has gotten much attention,” says Susan Swithers of Purdue University in West Lafayette, Ind. A key finding, she says: Brains of diet soda drinkers “don’t differentiate very well between sucrose and saccharin.” Erin Green and Claire Murphy of the University of California, San Diego and San Diego State University recruited 24 healthy young adults for a battery of brain imaging tests. Half reported regularly drinking sugar-free beverages, usually at least once a day. The rest seldom if ever consumed such drinks. While the brain scans were underway, the researchers pumped small amounts of saccharin- or sugar-sweetened water in random order into each recruit’s mouth as the volunteer rated the tastes. Both the diet soda drinkers and the nondrinkers rated each sweetener about equally pleasant and intense, Green and Murphy report in an upcoming Physiology & Behavior. But which brain regions lit up while making those judgments differed sharply based on who regularly consumed diet drinks. © Society for Science & the Public 2000 - 2012
By Ferris Jabr The human body is a tireless gardener, growing new cells throughout life in many organs—in the skin, blood, bones and intestines. Until the 1980s most scientists thought that brain cells were the exception: the neurons you are born with are the neurons you have for life. In the past three decades, however, researchers have discovered hints that the human brain produces new neurons after birth in two places: the hippocampus—a region important for memory—and the walls of fluid-filled cavities called ventricles, from which stem cells migrate to the olfactory bulb, a knob of brain tissue behind the eyes that processes smell. Studies have clearly demonstrated that such migration happens in mice long after birth and that human infants generate new neurons. But the evidence that similar neurogenesis persists in the adult human brain is mixed and highly contested. A new study relying on a unique form of carbon dating suggests that neurons born during adulthood rarely if ever weave themselves into the olfactory bulb's circuitry. In other words, people—unlike other mammals—do not replenish their olfactory bulb neurons, which might be explained by how little most of us rely on our sense of smell. Although the new research casts doubt on the renewal of olfactory bulb neurons in the adult human brain, many neuroscientists are far from ready to end the debate. In preparation for the new study, Olaf Bergmann and Jonas Frisén of the Karolinska Institute in Stockholm and their colleagues acquired 14 frozen olfactory bulbs from autopsies performed between 2005 and 2011 at the institute's Department of Forensic Medicine. To determine whether the neurons were younger than the people they came from—which would mean the cells were generated after birth—the researchers needed to isolate the cells' DNA. © 2012 Scientific American,
By Julie Wan, For many years, scientists agreed that human tongues perceived four basic tastes: sweet, sour, salty and bitter. Then in 2002, receptors were confirmed for a taste called umami — first proposed by a Japanese chemist in 1908 and commonly described as meatiness or savoriness — and it became widely accepted as the fifth basic taste. Since then, molecular biologists have theorized that humans may have as many as 20 distinct receptors for such tastes as calcium, carbonation, starch and even water. The data supporting each vary widely, but one contender for a sixth taste has begun to stand out from the rest: fat. The growing evidence is intriguing to scientists and food developers, who hope that a better understanding of our perception of fat will have applications in health and obesity management. But that’s far down the road. Currently, the debate is still over whether fat is a taste, and studies are increasingly likely to say that it is. In 2010, for example, researchers at Deakin University in Australia found that people were able to detect the taste of fatty acids. This year, researchers at the Center for Human Nutrition at Washington University School of Medicine in St. Louis said they had discovered that some people may be more sensitive to the presence of fat in foods than others. For the latter study, published in March in the Journal of Lipid Research, 21 people with a body mass index of 30 or more — considered clinically obese — tasted three solutions with a similarly viscous texture and were asked to identify the one that was different. © 1996-2012 The Washington Post
By Rachel Ehrenberg “Old people smell” is for real — and it isn’t mothballs, Jean Naté or pipe tobacco. It’s a mild and not unpleasant odor compared with the intense, unpleasant smell emitted by 40- to 50-something guys, a new study finds. Scientists don’t know what makes up this vintage chemical fingerprint, but the research suggests that apologies to your grandparents may be in order. The negative association with the smell of the elderly appears to be more about context than scent, says Johan Lundström of the Monell Chemical Senses Center in Philadelphia. Lundström and his colleagues collected underarm odors from 12 to 16 people in each of three age groups: young (20 to 30 years old), middle-aged (45 to 55 years old) and old (75 to 95 years old). For five nights while they slept, the study participants wore T-shirts with breast-feeding pads sewn in the underarms. The shirts and bed linens had been washed with scent-free soap and the participants did the same to themselves before going to bed each night. They also refrained from smoking, drinking alcohol or eating foods that are known to contribute odors to bodily secretions. Evaluators (aged 20 to 30) then sniffed the armpit pads. Evaluators rated the samples on pleasantness and intensity, guessed which of two odors came from the older donor and then labeled all of the scents by age category. The evaluators had trouble discerning young from middle-aged odors. But the odors from old donors were correctly identified more often than would be expected by chance, the research team reports online May 30 in PLoS ONE. © Society for Science & the Public 2000 - 2012
By AMANDA SCHAFFER When one fish is injured, others nearby may dart, freeze, huddle, swim to the bottom or leap from the water. The other fish know that their school mate has been harmed. But how? In the 1930s, Karl von Frisch, the famous ethologist, noted this behavior in minnows. He theorized that injured fish release a substance that is transmitted by smell and causes alarm. But Dr. von Frisch never identified the chemical composition of the signal. He just called it schreckstoff, or “scary stuff.” Schreckstoff is a long-standing biological mystery, but now researchers may have solved a piece of it. In a study published in February in Current Biology, Suresh Jesuthasan, a neuroscientist at the Biomedical Sciences Institutes in Singapore, and his colleagues isolated sugar molecules called chondroitins from the outer mucus of zebra fish. They found that when these molecules are broken into fragments, as they might be when the fish’s skin is injured, and added to water, they prompt alarm behavior in other fish. At low concentrations, the fish were “mildly perturbed,” Dr. Jesuthasan said. At high concentrations, they stopped darting altogether and froze in place for an hour or longer. He and his colleagues also showed that neurons in the olfactory bulb of these fish were activated when exposed to the sugar fragments. In a sense, the fish seemed to “smell” the injury. © 2012 The New York Times Company
by Elizabeth Norton Do our brains continue to produce neurons throughout our lifetimes? That's been one of the most hotly debated questions in the annals of science. Since the 1950s, studies have hinted at the possibility, but not until the late 1990s did research prove that the birth of new neurons, called neurogenesis, goes on in the brains of adult primates and humans. Now a surprising new study in humans shows that in the olfactory bulb-the interface between the nose and the brain and an area long—known to be a hot spot of neurogenesis—new neurons may be born but not survive. The finding may rule out neurogenesis in this area, or it might show only that some people don't stimulate their brains enough through the sense of smell, some researchers say. Previous studies have found evidence of neurogenesis in the olfactory bulb of adult humans. But those studies measured only proteins produced by immature neurons, leaving open the question of whether these youngsters ever grew up to connect with other cells to form functional networks, says neuroscientist Jonas Frisén of the Karolinska Institute in Stockholm. If new olfactory neurons really reached adulthood throughout a person's life, researchers should find neurons of a variety of ages in this region. That's not what Frisén and his team saw. The discovery is based on a technique he and his colleague Kirsty Spalding hit upon in 2005, in which they found a clever way to deduce the age of neurons. The method relies on atomic testing carried out in the 1950s and 1960s, which released massive amounts of carbon-14 into the atmosphere; the atmospheric 14C has been steadily declining ever since. Thus, the later a cell is born after this testing, the less 14C it contains. © 2010 American Association for the Advancement of Science.
By Jason G. Goldman Getting around is complicated business. Every year, animals traverse miles of sky and sea (and land), chasing warmth or food or mates as the planet rotates and the seasons change. And with such precision! Some animals rely on visual landmarks, others on subtle changes in magnetic fields, and yet others match their internal clocks with the movement of the sun and stars across the sky. One researcher, Jennifer A. Mather, wondered: how do octopuses navigate? Do they rely on chemotactile sensory information, or do they orient towards visual landmarks? Octopuses occupy “homes” for several days or in some instances for several weeks, and when they go out looking for food, they are sometimes gone for several hours at a time. Therefore, they must use some sort of memory to find their way back home. Many molluscs use trail-following, and follow their own mucus trails, or the trails of others. You might expect that octopuses use trail-following as well, since they forage by using chemotactile exploration – at least four different types of receptors on their suckers gather chemical and tactile information as they move along the rocky seafloor. However, many other species use visual scene recognition to aid in navigation: ants, bees, gerbils, hamsters, pigeons, and even humans, use visual landmarks to navigate around their environments. Since octopuses use visual information to distinguish among different objects, they could use visual landmarks to get home as well. © 2012 Scientific American
By Susan Milius New high-speed video of the tropical bats swooping toward various frogs and toads shows that the predators deploy a sequence of senses to update their judgment of prey during an attack to avoid eating a toxic amphibian, says behavioral ecologist Rachel Page of the Smithsonian Tropical Research Institute in Gamboa, Panama. The bats proved hard to fool even when researchers played the call of a favorite edible frog while offering up another species, Page and her colleagues report in an upcoming Naturwissenschaften. In the tropics, various bats will nab a frog if given half a chance, but only the fringe-lipped species (Trachops cirrhosus) is known to follow frog calls, such as the “tuuun chuck” call of the túngara frog (Engystomops pustulosus). In tests in Panama, Page and her colleagues found that fringe-lipped bats turned aside in mid-air if researchers broadcast enticing túngara calls but offered up a cane toad (Rhinella marina), which is way too big for a bat to carry off. The possibility that incoming bats might use echolocation to avoid overweight prey intrigues bat specialist Brock Fenton at the University of Western Ontario in Canada. Early studies of these bats largely ignored possible last-minute echolocation, he says. The new tests also revealed that playing túngara calls while offering a right-sized but toxic leaf litter toad (Rhinella alata) led bats to catch and then drop the unpleasant prey. (Both bats and toads survived.) © Society for Science & the Public 2000 - 2012
Link ID: 16840 - Posted: 05.26.2012