Chapter 6. Hearing, Balance, Taste, and Smell
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Nell Greenfieldboyce Picking a mate can be one of life's most important decisions. But sometimes people make a choice that seems to make no sense at all. And humans aren't the only ones — scientists have now seen apparently irrational romantic decisions in frogs. Little tungara frogs live in Central America, and they're found everywhere from forests to ditches to parking lot puddles. These frogs are only about 2 centimeters long, but they are loud. The males make calls to woo the females. Amanda Lea, a biologist in the laboratory of Mike Ryan at the University of Texas, Austin, says past studies have given scientists a pretty good idea of what the females find appealing. "They tend to like longer calls. They also like lower-frequency calls," says Lea. "Then, the other thing that's a really big one for these gals is the 'call rate.' They love faster call rates. The faster a male can call, the better." But in real life, love is complicated. Female frogs face countless suitors. So Lea and Ryan wondered: Would a female really always pick the male that scored highest on the froggy love-call meter? To find out, they put female frogs in a room with some loudspeakers. From one speaker the scientists played a recording of frog call that had a really fast rate. But other features in this voice were less attractive. Then the researchers played a second, different call for the female frogs. This voice was more attractive, but it was slower. The ladies had to make a choice. "They have two traits to evaluate," Lea explains. "They have the call rate and they have the attractiveness of the call." © 2015 NPR
Christopher Joyce Male treehoppers make their abdomens thrum like tuning forks to transmit very particular vibrating signals that travel down their legs and along leaf stems to other bugs — male and female. Male treehoppers make their abdomens thrum like tuning forks to transmit very particular vibrating signals that travel down their legs and along leaf stems to other bugs — male and female. Courtesy of Robert Oelman Animals, including humans, feel sound as well as hear it, and some of the most meaningful audio communication happens at frequencies that people can't hear. Elephants, for example, use these low-frequency rumbles to, among other things, find family or a mate across long distances. Whales do it, too. But you don't have to weigh a ton to rumble. In fact, you don't have to be bigger than a pea. Consider, for example, the treehopper, a curious little sap-sucking insect that lives on the stems of leaves. Or the tree cricket, which communicates by rubbing together tooth-like structures on its wings, the way you might draw your thumb across the teeth of a comb. University of Missouri biologist Rex Cocroft has spent much of his career listening closely to treehoppers. In 1999, a team from NPR's Radio Expeditions program rendezvoused with Cocroft at a locust tree in a backyard in Virginia. Soft-spoken and bespectacled, he was pressing a phonograph needle up against the stem of a leaf. © 2015 NPR
Dan Charles Ah, sugar — we love the sweetness, but not the calories. For more than a century, food technologists have been on a quest for the perfect, guilt-free substitute. Ah, sugar — we love the sweetness, but not the calories. For more than a century, food technologists have been on a quest for the perfect, guilt-free substitute. Ryan Kellman/NPR There's a new candidate in the century-old quest for perfect, guiltless sweetness. I encountered it at the annual meeting of the Institute of Food Technologists, a combination of Super Bowl, Mecca, and Disneyland for the folks who put the processing in processed food. It was right in the middle of the vast exhibition hall, at the Tate & Lyle booth. This is the company that introduced the British Empire to the sugar cube, back in 1875. A century later, it invented sucralose, aka Splenda. "We have a deep understanding of sweetening," says Michael Harrison, Tate & Lyle's vice president of new product development. This year, his company launched its latest gift to your sweet tooth. It's called allulose. "This is a rare sugar. A sugar that's found in nature," Harrison explains. Chemically speaking, it's almost identical to ordinary sugar. It has the same chemical formula as fructose and glucose, but the atoms of hydrogen and oxygen are arranged slightly differently. © 2015 NPR
A new clinical trial is set to begin in the United Kingdom using the powerful noses of dogs to detect prostate cancer in humans. While research has been done before, these are the first trials approved by Britain's National Health Service. The trials, at the Milton Keynes University Hospital in Buckinghamshire, will use animals from a nonprofit organization called Medical Detection Dogs, co-founded in 2008 by behavioral psychologist Claire Guest. "What we've now discovered is that lots of diseases and conditions — and cancer included — that they actually have different volatile organic compounds, these smelly compounds, that are associated with them," Guest tells NPR's Rachel Martin. "And dogs can smell them." The dogs offer an inexpensive, non-invasive method to accompany the existing blood tests for prostate cancer, which detect prostate-specific antigen, or PSA, Guest says. "It's a low false-negative but a very high false-positive, meaning that three out of four men that have a raised PSA haven't got cancer," she explains. "So the physician has a very difficult decision to make: Which of the four men does he biopsy? What we want to do is provide an additional test — not a test that stands alone but an additional test that runs alongside the current testing, which a physician can use as part of that patient's picture." The samples come to the dogs — the dogs never go to the patient. At the moment, our dogs would be screening about between a .5- to 1-ml drop of urine [or 1/5 to 1/10 teaspoon], so a very small amount. In the early days, of course, we know whether the samples have come from a patient with cancer or if the patient has another disease or condition, or is in fact healthy. © 2015 NPR
Keyword: Chemical Senses (Smell & Taste)
Link ID: 21302 - Posted: 08.17.2015
Teresa Shipley Feldhausen Move over, umami. Fat is the newest member of the pantheon of basic tastes, joining salty, sweet, sour, bitter and savory, or umami. Researchers at Purdue University in West Lafayette, Ind., conducted taste tests pitting a variety of fats against flavors in the other taste categories, such as monosodium glutamate for umami. The result: People recognize some fats as separate from the other five taste categories, even with plugged noses. The researchers dub this sixth sense oleogustus. For instance, nearly two-thirds of tasters identified one type of fat — linoleic acid, found in vegetable and nut oils — as a distinct flavor. Texture wasn’t a factor; the researchers whipped up tasting samples that gave the same mouthfeel. Pure oleogustus doesn’t invoke notes of olive oil or fresh butter. It’s unpleasant, the researchers report online July 3 in Chemical Senses. Mix oleogustus with some of the other five flavors, however, and you could end up with doughnuts or potato chips. Citations C.A. Running, B.A. Craig and R.D. Mattes. Oleogustus: The unique taste of fat. Chemical Senses. Published online July 3, 2015. doi: 10.1093/chemse/bjv036. © Society for Science & the Public 2000 - 2015.
Keyword: Chemical Senses (Smell & Taste)
Link ID: 21252 - Posted: 08.02.2015
By Gary Stix A decline in hearing acuity is not only an occurrence that happens in the aged. An article in the August Scientific American by M. Charles Liberman, a professor of otology and laryngology at Harvard Medical School and director of the Eaton-Peabody Laboratories at Massachusetts Eye and Ear, focuses on relatively recent discoveries that show the din of a concert or high-decibel machine noise is enough to cause some level of hearing damage. After reading the article check out this video by medical illustrator Brandon Pletsch and its narrated animation explaining how the sensory system that detects sound functions. © 2015 Scientific American
Link ID: 21250 - Posted: 08.02.2015
By David Noonan Leaping through the air with ease and spinning in place like tops, ballet dancers are visions of the human body in action at its most spectacular and controlled. Their brains, too, appear to be special, able to evade the dizziness that normally would result from rapid pirouettes. When compared with ordinary people's brains, researchers found in a study published early this year, parts of dancers' brains involved in the perception of spinning seem less sensitive, which may help them resist vertigo. For millions of other people, it is their whole world, not themselves, that suddenly starts to whirl. Even the simplest task, like walking across the room, may become impossible when vertigo strikes, and the condition can last for months or years. Thirty-five percent of adults older than 39 in the U.S.—69 million people—experience vertigo at one time or another, often because of damage to parts of the inner ear that sense the body's position or to the nerve that transmits that information to the brain. Whereas drugs and physical therapy can help many, tens of thousands of people do not benefit from existing treatments. “Our patients with severe loss of balance have been told over and over again that there's nothing we can do for you,” says Charles Della Santina, an otolaryngologist who studies inner ear disorders and directs the Johns Hopkins Vestibular NeuroEngineering Laboratory. Steve Bach's nightmare started in November 2013. The construction manager was at home in Parsippany, N.J. “All of a sudden the room was whipping around like a 78 record,” says Bach, now age 57. He was curled up on the living room floor in a fetal position when his daughter found him and called 911. He spent the next five days in the hospital. © 2015 Scientific American
Keyword: Movement Disorders
Link ID: 21248 - Posted: 08.01.2015
Michael Sullivan It's 5:45 in the morning, and in a training field outside Siem Reap, home of Angkor Wat, Cambodia's demining rats are already hard at work. Their noses are close to the wet grass, darting from side to side, as they try to detect explosives buried just beneath the ground. Each rat is responsible for clearing a 200-square-meter (239-square-yard) patch of land. Their Cambodian supervisor, Hulsok Heng, says they're good at it. "They are very good," he says. "You see this 200 square meters? They clear in only 30 minutes or 35 minutes. If you compare that to a deminer, maybe two days or three days. The deminer will pick up all the fragmentation, the metal in the ground, but the rat picks up only the smell of TNT. Not fragmentation or metal or a nail or a piece of crap in the ground." That's right: Someone using a metal-detecting machine will take a lot longer to detect a land mine than a rat using its nose. There's plenty of work for the rats here in Cambodia. The government estimates there are 4 million to 6 million land mines or other pieces of unexploded ordnance — including bombs, shells and grenades — littering the countryside, remnants of decades of conflict. Neighboring Vietnam and Laos also have unexploded ordnance left over from the Vietnam War. Dozens of people are killed or maimed in the region every year — and there's a financial toll as well, since the presence of these potentially deadly devices decreases the amount of land available to farmers. © 2015 NPR
By THE ASSOCIATED PRESS WASHINGTON — Move over sweet and salty: Researchers say we have a distinct and basic taste for fat, too. But it's nowhere near as delicious as it sounds. They propose expanding our taste palate to include fat along with sweet, salty, bitter, sour and relative newcomer umami. A research team at Purdue University tested look-alike mixtures with different tastes. More than half of the 28 special tasters could distinguish fatty acids from the other tastes, according to a study published in the journal Chemical Senses. Past research showed fat had a distinct feel in the mouth, but scientists removed texture and smell clues and people could still tell the difference. "The fatty acid part of taste is very unpleasant," study author Richard Mattes, a Purdue nutrition science professor, said Thursday. "I haven't met anybody who likes it alone. You usually get a gag reflex." Stinky cheese has high levels of the fat taste and so does food that goes rancid, Mattes said. Yet we like it because it mixes well and brings out the best of other flavors, just like the bitter in coffee or chocolate, he added. To qualify as a basic taste, a flavor has to have unique chemical signature, have specific receptors in our bodies for the taste, and people have to distinguish it from other tastes. Scientists had found the chemical signature and two specific receptors for fat, but showing that people could distinguish it was the sticky point. Initially Mattes found that people couldn't quite tell fat tastes when given a broad array of flavors. But when just given yucky tastes — bitter, umami, sour — they could find the fat. © 2015 The New York Times Company
Chris Woolston A study that did not find cognitive benefits of musical training for young children triggered a “media firestorm”. Researchers often complain about inaccurate science stories in the popular press, but few air their grievances in a journal. Samuel Mehr, a PhD student at Harvard University in Cambridge, Massachusetts, discussed in a Frontiers in Psychology article1 some examples of media missteps from his own field — the effects of music on cognition. The opinion piece gained widespread attention online. Arseny Khakhalin, a neuroscientist at Bard College in Annandale-on-Hudson, New York, tweeted: Mehr gained first-hand experience of the media as the first author of a 2013 study in PLoS ONE2. The study involved two randomized, controlled trials of a total of 74 four-year-olds. For children who did six weeks of music classes, there was no sign that musical activities improved scores on specific cognitive tests compared to children who did six weeks of art projects or took part in no organized activities. The authors cautioned, however, that the lack of effect of the music classes could have been a result of how they did the studies. The intervention in the trials was brief and not especially intensive — the children mainly sang songs and played with rhythm instruments — and older children might have had a different response than the four-year-olds. There are many possible benefits of musical training, Mehr said in an interview, but finding them was beyond the scope of the study. © 2015 Nature Publishing Group
By Hanae Armitage Playing an instrument is good for your brain. Compared to nonmusicians, young children who strum a guitar or blow a trombone become better readers with better vocabularies. A new study shows that the benefits extend to teenagers as well. Neuroscientists compared two groups of high school students over 3 years: One began learning their first instrument in band class, whereas the other focused on physical fitness in Junior Reserve Officers’ Training Corps (JROTC). At the end of 3 years, those students who had played instruments were better at detecting speech sounds, like syllables and words that rhyme, than their JROTC peers, the team reports online today in the Proceedings of the National Academy of Sciences. Researchers know that as children grow up, their ability to soak up new information, especially language, starts to diminish. These findings suggest that musical training could keep that window open longer. But the benefits of music aren’t just for musicians; taking up piano could be the difference between an A and a B in Spanish class. © 2015 American Association for the Advancement of Science
By C. CLAIBORNE RAY Q. Can you hear without an intact eardrum? A. “When the eardrum is not intact, there is usually some degree of hearing loss until it heals,” said Dr. Ashutosh Kacker, an ear, nose and throat specialist at NewYork-Presbyterian Hospital and a professor at Weill Cornell Medical College, “but depending on the size of the hole, you may still be able to hear almost normally.” Typically, Dr. Kacker said, the larger an eardrum perforation is, the more severe the hearing loss it will cause. The eardrum, or tympanic membrane, is a thin, cone-shaped, pearly gray tissue separating the outer and middle ear canals, he explained. Soundwaves hit the eardrum, which in turn vibrates the bones of the middle ear. The bones pass the vibration to the cochlea, which leads to a signal cascade culminating in the sound being processed by the brain and being heard. There are several ways an eardrum can be ruptured, Dr. Kacker said, including trauma, exposure to sudden or very loud noises, foreign objects inserted deeply into the ear canal, and middle-ear infection. “Usually, the hole will heal by itself and hearing will improve within about two weeks to a few months, especially in cases where the hole is small,” he said. Sometimes, when the hole is larger or does not heal well, surgery will be required to repair the eardrum. Most such operations are done by placing a patch over the hole to allow it to heal, and the surgery is usually very successful in restoring hearing, Dr. Kacker said. © 2015 The New York Times Company
Link ID: 21187 - Posted: 07.20.2015
Jon Hamilton It's almost impossible to ignore a screaming baby. (Click here if you doubt that.) And now scientists think they know why. "Screams occupy their own little patch of the soundscape that doesn't seem to be used for other things," says David Poeppel, a professor of psychology and neuroscience at New York University and director of the Department of Neuroscience at the Max Planck Institute in Frankfurt. And when people hear the unique sound characteristics of a scream — from a baby or anyone else — it triggers fear circuits in the brain, Poeppel and a team of researchers report in Cell Biology. The team also found that certain artificial sounds, like alarms, trigger the same circuits. "That's why you want to throw your alarm clock on the floor," Poeppel says. The researchers in Poeppel's lab decided to study screams in part because they are a primal form of communication found in every culture. And there was another reason. "Many of the postdocs in my lab are in the middle of having kids and, of course, screams are very much on their mind," Poeppel says. "So it made perfect sense for them to be obsessed with this topic." The team started by trying to figure out "what makes a scream a scream," Poeppel says. Answering that question required creating a large database of recorded screams — from movies, from the Internet and from volunteers who agreed to step into a sound booth. A careful analysis of these screams found that they're not like any other sound that people make, including other loud, high-pitched vocalizations. The difference is something called the amplitude modulation rate, which is how often the loudness of a sound changes. © 2015 NPR
That song really is stuck in your head. The experience of hearing tunes in your mind appears to be linked to physical differences in brain structure. The study is the first to look at the neural basis for “involuntary musical imagery” – or “earworms”. They aren’t just a curiosity, says study co-author Lauren Stewart at Goldsmith’s, University of London, but could have a biological function. Stewart, a music psychologist, was first inspired to study earworms by a regular feature on the radio station BBC 6Music, in which listeners would write in with songs they had woken up with in their heads. There was a lot of interest from the public in what they are and where they had come from, but there was little research on the topic, she says. Once Stewart and her team started researching earworms, it became clear that some people are affected quite severely: one person even wrote to them saying he had lost his job because of an earworm. To find out what makes some people more susceptible to the phenomenon, the team asked 44 volunteers about how often they got earworms and how they were affected by them. Then they used MRI scans to measure the thickness of volunteers’ cerebral cortices and the volume of their grey matter in various brain areas. Brain differences People who suffered earworms more frequently had thicker cortices in areas involved in auditory perception and pitch discrimination. © Copyright Reed Business Information Ltd.
By Sarah Schwartz In a possible step toward treating genetic human deafness, scientists have used gene therapy to partially restore hearing in deaf mice. Some mice with genetic hearing loss could sense and respond to noises after receiving working copies of their faulty genes, researchers report July 8 in Science Translational Medicine. Because the mice’s mutated genes closely correspond to those responsible for some hereditary human deafness, the scientists hope the results will inform future human therapies. “I would call this a really exciting big step,” says otolaryngologist Lawrence Lustig of Columbia University Medical Center. The ear’s sound-sensing hair cells convert noises into information the brain can process. Hair cells need specific proteins to work properly, and alterations in the genetic blueprints for these proteins can cause deafness. To combat the effects of two such mutations, the scientists injected viruses containing healthy genes into the ears of deaf baby mice. The virus infected some hair cells, giving them working genes. The scientists tried this therapy on two different deafness-causing mutations. Within a month, around half the mice with one mutation showed brainwave activity consistent with hearing and jumped when exposed to loud noises. Treated mice with the other mutation didn’t respond to noises, but the gene therapy helped their hair cells — which normally die off quickly due to the mutation — survive. All of the untreated mice remained deaf. © Society for Science & the Public 2000 - 2015
By SINDYA N. BHANOO It may be possible to diagnose autism by giving children a sniff test, a new study suggests. Most people instinctively take a big whiff when they encounter a pleasant smell and limit their breathing when they encounter a foul smell. Children with autism spectrum disorder don’t make this natural adjustment, said Liron Rozenkrantz, a neuroscientist at the Weizmann Institute of Science in Israel and one of the researchers involved with the study. She and her colleagues report their findings in the journal Current Biology. They presented 18 children who had an autism diagnosis and 18 typically developing children with pleasant and unpleasant odors and measured their sniff responses. The pleasant smells were rose and soap, and the unpleasant smells were sour milk and rotten fish. Typically developing children adjusted their sniffing almost immediately — within about 305 milliseconds. Children with autism did not respond as rapidly. As they were exposed to the smells, the children were watching a cartoon or playing a video game. “It’s a semi-automated response,” Ms. Rozenkrantz said. “It does not require the subject’s attention.” Using the sniff test alone, the researchers, who had not been told which children had autism, were able to correctly identify those with autism 81 percent of the time. They also found that the farther removed an autistic child’s sniff response was from the average for typically developing children, the more severe the child’s social impairments were. © 2015 The New York Times Company
By Victoria Gill Science reporter, BBC News Cat v mouse: it is probably the most famous predator-prey pairing, enshrined in idioms and a well-known cartoon. And cats, it turns out, even have chemical warfare in their anti-mouse arsenal - contained in their urine. Researchers found that when very young mice were exposed to a chemical in cat urine, they were less likely to avoid the scent of cats later in life. The findings were presented at the Society for Experimental Biology's annual meeting in Prague. The researchers, from the AN Severtov Institute of Ecology and Evolution in Moscow, had previously found that the compound - aptly named felinine - causes pregnant mice to abort. Dr Vera Voznessenskaya explained that mice have a physiological response to this cat-specific compound. Chemical-sensing mouse neurons in the mouse's brain pick up the scent, triggering a reaction which includes an increase in the levels of stress hormones. "It's something that has existed in cats and mice for thousands of years," said Dr Voznessenskaya. This new study revealed that baby mice exposed to the compound during a "critical period" in their development would, as adults, react quite differently to their arch enemy's smell. The team exposed one-month-old mice to the chemical over two weeks. When they were tested later for their reaction, they were much less likely to flee the same scent. The interaction between cats and mice has a long history "Their physical sensitivity [to the chemical] was actually actually much higher," Dr Voznessenskaya explained. "More of their receptors detect the compound and they produce higher levels of stress hormone." Despite this though, mice raised around the unmistakable scent of cat pee are less inclined to show signs of fear, or to flee when they sniff it out. © 2015 BBC.
by Sarah Zielinski Seabirds called shearwaters manage to navigate across long stretches of open water to islands where the birds breed. It’s not been clear how the birds do this, but there have been some clues. When scientists magnetically disturbed Cory’s shearwaters, the birds still managed to find their way. But when deprived of their sense of smell, the shearwaters had trouble homing in on their final destination. Smell wouldn’t seem to be all that useful out over the ocean, especially with winds and other atmospheric disturbances playing havoc on any scents wafting through the air. But now researchers say they have more evidence that shearwaters are using olfactory cues to navigate. Andrew Reynolds of Rothamsted Research in Harpenden, England, and colleagues make their case June 30 in the Proceedings of the Royal Society B. Messing with Cory’s shearwaters or other seabirds, like researchers did in earlier studies, wasn’t a good option, the researchers say, because there are conservation concerns when it comes to these species. Instead, they attached tiny GPS loggers to 210 shearwaters belonging to three species: Cory’s shearwaters, Scopoli’s shearwaters and Cape Verde shearwaters. But how would the birds’ path reveal how they were navigating? If they were using olfactory cues, the team reasoned, the birds wouldn’t take a straight path to their target. Instead, they would fly straight for a time, guided in that direction by a particular smell. When they lost that scent, their direction would change, until they picked up another scent that could guide them. And only when a bird got close would it use landmarks, other birds and the odor of the breeding colony as guides. If the birds were using some other method of navigation — or randomly searching for where to go — their paths would look much different. © Society for Science & the Public 2000 - 2015
By Christopher Intagliata Two decades ago, Swiss researchers had women smell the tee shirts that various men had slept in for two nights. Turned out that if women liked the aroma of a particular shirt, the guy who’d worn it was likely to have genetically coded immunity that was unlike the woman’s. Well the effect isn't just limited to sweaty shirts. Turns out we all smell things a little differently—you pick up a note of cloves, say, where I smell something more soapy—and that too gives clues to our degree of genetic similarity. Researchers tried that test with 89 people—having them sniff a couple dozen samples, and label each one using terms like lemony, coconut, fishy and floral. And each volunteer classified the scents differently enough that the researchers could single them out in subsequent tests, based on what they called each subject’s "olfactory fingerprint." Researchers then repeated that sniff test on another 130 subjects. But this time they did a blood test, too, to figure out each person's HLA type—an immune factor that determines whether you'll reject someone's organ, for example. They found that people who perceived smells similarly also had similar HLA types. Study author Lavi Secundo, a neuroscientist at the Weizmann Institute of Science in Israel, says the smell test could have real-world applications. "For organ donation you can think of this method as a quick, maybe a quick and dirty, method to sift between the best and the rest." He and his colleagues say it might even eliminate the need for 30 percent of the HLA tests done today. The work appears in the Proceedings of the National Academy of Sciences. [Lavi Secundo et al, Individual olfactory perception reveals meaningful nonolfactory genetic information] © 2015 Scientific American
By Sarah Lewin Evolutionary biologists have long wondered why the eardrum—the membrane that relays sound waves to the inner ear—looks in humans and other mammals remarkably like the one in reptiles and birds. Did the membrane and therefore the ability to hear in these groups evolve from a common ancestor? Or did the auditory systems evolve independently to perform the same function, a phenomenon called convergent evolution? A recent set of experiments performed at the University of Tokyo and the RIKEN Evolutionary Morphology Laboratory in Japan resolves the issue. When the scientists genetically inhibited lower jaw development in both fetal mice and chickens, the mice formed neither eardrums nor ear canals. In contrast, the birds grew two upper jaws, from which two sets of eardrums and ear canals sprouted. The results, published in Nature Communications, confirm that the middle ear grows out of the lower jaw in mammals but emerges from the upper jaw in birds—all supporting the hypothesis that the similar anatomy evolved independently in mammals and in reptiles and birds. (Scientific American is part of Springer Nature.) Fossils of auditory bones had supported this conclusion as well, but eardrums do not fossilize and so could not be examined directly. © 2015 Scientific American