Chapter 6. Hearing, Balance, Taste, and Smell

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Terry Gross Food science writer Harold McGee was in the middle of writing Nose Dive, his book about the science of smell, when he woke up one morning and realized that he couldn't smell his own coffee. Loss of smell has since become associated with COVID-19. In McGee's case, it was the byproduct of a sinus infection. McGee remembers feeling panicked. "I have friends in the kind of clinical side of taste and smell research. And so I immediately contacted them to find out what I could do and why this had happened," he says. "And they basically said, 'You're going to have to wait and see.' " Over the course of a few months, McGee's sense of smell gradually returned. But he still remembers what it was like to live in an odorless world. "It's the kind of thing where you don't notice something until it's gone," he says. "I spent less and less time cooking. There was no point in going out to restaurants because I wasn't really going to enjoy it." McGee's new book is about how smell is essential to our sense of taste, why things smell the way they do and the ways different chemicals combine to create surprising (and sometimes distasteful) odors. "One of the great pleasures of delving into smells in general was discovering over and over again that things that we enjoy in foods are actually found elsewhere in the world," he says. "And in as unlikely places as cat pee and human sweat, for example." © 2020 npr

Keyword: Chemical Senses (Smell & Taste)
Link ID: 27583 - Posted: 11.16.2020

By Jonathan Lambert Octopus arms have minds of their own. Each of these eight supple yet powerful limbs can explore the seafloor in search of prey, snatching crabs from hiding spots without direction from the octopus’ brain. But how each arm can tell what it’s grasping has remained a mystery. Now, researchers have identified specialized cells not seen in other animals that allow octopuses to “taste” with their arms. Embedded in the suckers, these cells enable the arms to do double duty of touch and taste by detecting chemicals produced by many aquatic creatures. This may help an arm quickly distinguish food from rocks or poisonous prey, Harvard University molecular biologist Nicholas Bellono and his colleagues report online October 29 in Cell. The findings provide another clue about the unique evolutionary path octopuses have taken toward intelligence. Instead of being concentrated in the brain, two-thirds of the nerve cells in an octopus are distributed among the arms, allowing the flexible appendages to operate semi-independently (SN: 4/16/15). “There was a huge gap in knowledge of how octopus [arms] actually collect information about their environment,” says Tamar Gutnick, a neurobiologist who studies octopuses at Hebrew University of Jerusalem who was not involved in the study. “We’ve known that [octopuses] taste by touch, but knowing it and understanding how it’s actually working is a very different thing.” Working out the specifics of how arms sense and process information is crucial for understanding octopus intelligence, she says. “It’s really exciting to see someone taking a comprehensive look at the cell types involved,” and how they work. © Society for Science & the Public 2000–2020

Keyword: Chemical Senses (Smell & Taste); Evolution
Link ID: 27560 - Posted: 10.31.2020

By Lucy Hicks Ogre-faced spiders might be an arachnophobe’s worst nightmare. The enormous eyes that give them their name allow them to see 2000 times better than we can at night. And these creepy crawlers are lightning-fast predators, snatching prey in a fraction of a second with mini, mobile nets. Now, new research suggests these arachnids use their legs not only to scuttle around, but also to hear. In light of their excellent eyesight, this auditory skill “is a surprise,” says George Uetz, who studies the behavioral ecology of spiders at the University of Cincinnati and wasn’t involved in the new research. Spiders don’t have ears—generally a prerequisite for hearing. So, despite the vibration-sensing hairs and receptors on most arachnids’ legs, scientists long thought spiders couldn’t hear sound as it traveled through the air, but instead felt vibrations through surfaces. The first clue they might be wrong was a 2016 study that found that a species of jumping spider can sense vibrations in the air from sound waves. Enter the ogre-faced spider. Rather than build a web and wait for their prey, these fearsome hunters “take a much more active role,” says Jay Stafstrom, a sensory ecologist at Cornell University. The palm-size spiders hang upside down from small plants on a silk line and create a miniweb across their four front legs, which they use as a net to catch their next meal. The spiders either lunge at bugs wandering below or flip backward to ensnare flying insects’ midair. © 2020 American Association for the Advancement of Science.

Keyword: Hearing; Evolution
Link ID: 27559 - Posted: 10.31.2020

By Nicholas Bakalar Long-term exposure to noise may be linked to an increased risk for Alzheimer’s disease and other forms of dementia. Researchers did periodic interviews with 5,227 people 65 and older participating in a study on aging. They assessed them with standard tests of orientation, memory and language, and tracked average daytime noise levels in their neighborhoods for the five years preceding the cognitive assessments. About 11 percent had Alzheimer’s disease, and 30 percent had mild cognitive impairment, which often progresses to full-blown dementia. Residential noise levels varied widely, from 51 to 78 decibels, or from the level of a relatively quiet suburban neighborhood to that of an urban setting near a busy highway. The study is in Alzheimer’s & Dementia. After controlling for education, race, smoking, alcohol consumption, neighborhood air pollution levels and other factors, they found that each 10 decibel increase in community noise level was associated with a 36 percent higher likelihood of mild cognitive impairment, and a 29 percent increased risk for Alzheimer’s disease. The associations were strongest in poorer neighborhoods, which also had higher noise levels. The reasons for the connection are unknown, but the lead author, Jennifer Weuve, an associate professor of epidemiology at Boston University, suggested that excessive noise can cause sleep deprivation, hearing loss, increased heart rate, constriction of the blood vessels and elevated blood pressure, all of which are associated with an increased risk for dementia. © 2020 The New York Times Company

Keyword: Alzheimers; Hearing
Link ID: 27551 - Posted: 10.28.2020

By Stephani Sutherland Many of the symptoms experienced by people infected with SARS-CoV-2 involve the nervous system. Patients complain of headaches, muscle and joint pain, fatigue and “brain fog,” or loss of taste and smell—all of which can last from weeks to months after infection. In severe cases, COVID-19 can also lead to encephalitis or stroke. The virus has undeniable neurological effects. But the way it actually affects nerve cells still remains a bit of a mystery. Can immune system activation alone produce symptoms? Or does the novel coronavirus directly attack the nervous system? Some studies—including a recent preprint paper examining mouse and human brain tissue—show evidence that SARS-CoV-2 can get into nerve cells and the brain. The question remains as to whether it does so routinely or only in the most severe cases. Once the immune system kicks into overdrive, the effects can be far-ranging, even leading immune cells to invade the brain, where they can wreak havoc. Some neurological symptoms are far less serious yet seem, if anything, more perplexing. One symptom—or set of symptoms—that illustrates this puzzle and has gained increasing attention is an imprecise diagnosis called “brain fog.” Even after their main symptoms have abated, it is not uncommon for COVID-19 patients to experience memory loss, confusion and other mental fuzziness. What underlies these experiences is still unclear, although they may also stem from the body-wide inflammation that can go along with COVID-19. Many people, however, develop fatigue and brain fog that lasts for months even after a mild case that does not spur the immune system to rage out of control. Another widespread symptom called anosmia, or loss of smell, might also originate from changes that happen without nerves themselves getting infected. Olfactory neurons, the cells that transmit odors to the brain, lack the primary docking site, or receptor, for SARS-CoV-2, and they do not seem to get infected. Researchers are still investigating how loss of smell might result from an interaction between the virus and another receptor on the olfactory neurons or from its contact with nonnerve cells that line the nose. © 2020 Scientific American,

Keyword: Learning & Memory; Chemical Senses (Smell & Taste)
Link ID: 27547 - Posted: 10.24.2020

Frank R. Lin, M.D., Ph.D. When I was going through my otolaryngology residency at Johns Hopkins in the early 2000s, I was struck by the disparity between how hearing loss was managed in children and in older adults. In the case of the child, it was a medical priority to ensure access to a hearing aid so he or she could communicate optimally at home and in school, and such devices were covered by insurance. This approach was justified based on extensive research demonstrating that hearing loss could have a substantial impact on a child’s cognitive and brain development, with lifetime consequences for educational and vocational achievement. For the older adult, the approach was radically different, even if the degree of hearing impairment was the same as in the child. The adult would be reassured that the deficit was to be expected, based on his or her age, and told that a hearing aid, if desired, would represent an out-of-pocket expense averaging about $4,000. Medicare provided no coverage for hearing aids. There was no robust research demonstrating meaningful consequences of hearing loss for older adults, as there was for children, and the clinical approach was typically guided by the notion that it was a very common, and hence inconsequential, aspect of aging. But this approach didn’t make sense, given what I had observed clinically. Older adults with hearing loss recounted to me their sense of isolation and loneliness, and the mental fatigue of constantly concentrating in trying to follow conversations. Family members would often describe a decline in patients’ general well-being and mental acuity as they struggled to hear. For those who obtained effective treatment for their hearing loss with hearing aids or a cochlear implant, the effects were often equally dramatic. Patients spoke of reengaging with family, no longer getting fatigued from straining to listen, and becoming their “old selves” again. If hearing was fundamentally important for children and represented a critical sensory input that could affect brain function, wouldn’t loss of hearing have corresponding implications for the aging brain and its function? © 2020 The Dana Foundation.

Keyword: Hearing; Alzheimers
Link ID: 27525 - Posted: 10.16.2020

By Katherine J. Wu Researchers in Iceland have identified a new mutant superpower — but the genetic trait probably won’t be granting anyone admission to the X-Men. A small contingent of the world’s population carries a mutation that makes them immune to the odious funk that wafts off fish, according to a study of some 11,000 people published Thursday in the journal Current Biology. The trait is rare, but potent: When faced with a synthetic odor that would put many people off their lunch, some test subjects smelled only the pleasant aroma of caramel, potato or rose. The vast majority of people aren’t so lucky. Nearly 98 percent of Icelanders, the research said, are probably as put off by the scent as you’d expect. The mutation is thought to be even rarer in populations in other countries. “I can assure you I do not have this mutation,” said Dr. Kári Stefánsson, a neurologist and the study’s senior author. “I tend to get nauseated when I get close to fish that is not completely fresh.” Dr. Stefánsson is the founder and chief executive of deCODE genetics, a biopharmaceutical company in Iceland’s capital, Reykjavik, which has been parsing the human genome for several decades. The team’s latest caper involved a deep dive into the underappreciated sense of olfaction. Study participants were asked to take a whiff of six Sniffin’ Sticks — pens imbued with synthetic odors resembling the recognizable scents of cinnamon, peppermint, banana, licorice, lemon and fish. They were asked to identify the smell, then rate its intensity and pleasantness. The older the study subjects were, the more they struggled to accurately pinpoint the scents. That’s unsurprising, given that sensory functions tend to decline later in life, said Rósa Gísladóttir, the study’s lead author. But even younger people didn’t always hit the mark, she said. The lemon and banana sticks, for instance, prompted descriptions of gummy bears and other candy-sweet smells. © 2020 The New York Times Company

Keyword: Chemical Senses (Smell & Taste); Genes & Behavior
Link ID: 27519 - Posted: 10.10.2020

By Cathleen O’Grady Tinnitus—a constant ringing or buzzing in the ears that affects about 15% of people—is difficult to understand and even harder to treat. Now, scientists have shown shocking the tongue—combined with a carefully designed sound program—can reduce symptoms of the disorder, not just while patients are being treated, but up to 1 year later. It’s “really important” work, says Christopher Cederroth, a neurobiologist at the University of Nottingham, University Park, who was not involved with the study. The finding, he says, joins other research that has shown “bimodal” stimulation—which uses sound alongside some kind of gentle electrical shock—can help the brain discipline misbehaving neurons. Hubert Lim, a biomedical engineer at the University of Minnesota, Twin Cities, hit on the role of the tongue in tinnitus by accident. A few years ago, he experimented with using a technique called deep brain stimulation to restore his patients’ hearing. When he inserted a pencil-size rod covered in electrodes directly into the brains of five patients, some of those electrodes landed slightly outside the target zone—a common problem with deep brain stimulation, Lim says. Later, when he started up the device to map out its effects on the brain, a patient who had been bothered by ringing ears for many years, said, “Oh, my tinnitus! I can’t hear my tinnitus,” Lim recalls. With certain kinds of tinnitus, people hear real sounds. For instance, there might be repeated muscular contractions in the ear, Lim says. But for many people, it’s the brain that’s to blame, perceiving sounds that aren’t there. One potential explanation for the effect is that hearing loss causes the brain to overcompensate for the frequencies it can no longer hear. © 2020 American Association for the Advancement of Science.

Keyword: Hearing; Attention
Link ID: 27517 - Posted: 10.10.2020

By Ian Randall It’s one of life’s little ironies: Sweet foods get sweeter when you add a little salt. Now, scientists may have provided connoisseurs of salted caramel and grapefruit with the reason this culinary trick is worth its salt. Your ability to savor food comes from the receptor cells in your tongue’s taste buds. Sweet tastes are detected by a family of receptors called T1R, which pick up both natural sugars and artificial sweeteners. Scientists originally thought disabling the T1R family would stop any responses to sweet stimuli. But in 2003, researchers showed that mice whose T1R genes had been genetically “knocked out” still liked the sugar glucose. The finding suggested there must be another way that mice—and possibly humans—sense sweetness. Seeking an explanation, physiologist Keiko Yasumatsu of Tokyo Dental Junior College and colleagues turned to a protein that works with glucose elsewhere in the body: sodium-glucose cotransporter 1 (SGLT1). In the kidneys and intestine, SGLT1 uses sodium to carry glucose into cells to provide them with energy. Curiously, the protein is also found in sweet-responsive taste cells. The researchers rubbed the tongues of unconscious T1R mice with a solution of glucose and salt—which contains the sodium SGLT1 needs to work—and recorded the responses of nerves connected to their taste cells. The salt seemed to make all the difference: It caused the rodents’ nerves to fire more rapidly, compared with mutated mice given only glucose. Conscious mice also seemed to show a preference for the sugar-salt solution. But this only worked with glucose; sweeteners like saccharin didn’t trigger a response. © 2020 American Association for the Advancement of Science.

Keyword: Chemical Senses (Smell & Taste)
Link ID: 27510 - Posted: 10.07.2020

Jon Henley Europe correspondent Four Covid-19 sniffer dogs have begun work at Helsinki airport in a state-funded pilot scheme that Finnish researchers hope will provide a cheap, fast and effective alternative method of testing people for the virus. A dog is capable of detecting the presence of the coronavirus within 10 seconds and the entire process takes less than a minute to complete, according to Anna Hielm-Björkman of the University of Helsinki, who is overseeing the trial. “It’s very promising,” said Hielm-Björkman. “If it works, it could prove a good screening method in other places” such as hospitals, care homes and at sporting and cultural events. After collecting their luggage, arriving international passengers are asked to dab their skin with a wipe. In a separate booth, the beaker containing the wipe is then placed next to others containing different control scents – and the dog starts sniffing. If it indicates it has detected the virus – usually by yelping, pawing or lying down – the passenger is advised to take a free standard polymerase chain reaction (PCR) test, using a nasal swab, to verify the dog’s verdict. In the university’s preliminary tests, dogs – which have been successfully used to detect diseases such as cancer and diabetes – were able to identify the virus with nearly 100% accuracy, even days before before a patient developed symptoms. Scientists are not yet sure what exactly it is that the dogs sniff when they detect the virus. A French study published in June concluded that there was “very high evidence” that the sweat odour of Covid-positive people was different to that of those who did not have the virus, and that dogs could detect that difference. Dogs are also able to identify Covid-19 from a much smaller molecular sample than PCR tests, Helsinki airport said, needing only 10-100 molecules to detect the presence of the virus compared with the 18m needed by laboratory equipment. © 2020 Guardian News & Media Limited

Keyword: Chemical Senses (Smell & Taste)
Link ID: 27490 - Posted: 09.25.2020

Researchers say mother bats use baby talk to communicate with their pups. Experts say that it helps bats learn the language. MARY LOUISE KELLY, HOST: You know how scientists are always curious? Well, one scientist started wondering if bats do something that humans do. AHANA AURORA FERNANDEZ: When we humans talk to a baby, we automatically change our voices. Hello, my baby. You are so cute. My voice goes up. SACHA PFEIFFER, HOST: That's Ahana Aurora Fernandez. She's in Berlin but did her bat study in Panama. And she found that, as many humans do, mommy bats talk to baby bats in a similar way. There's a word for this way of talking. It's motherese (ph). Experts say that in humans - and, apparently, also in bats - it helps with language learning. KELLY: Ahana Fernandez sent us recordings she made to illustrate her findings. They are slowed down so we can better hear the differences between adult bats talking to each other and the motherese used on bat pups. First, here's two adult bats talking to each other. KELLY: OK, and now here's a mother bat with her pup. PFEIFFER: It took patience for Ahana Hernandez to record bat conversation. She sat in the jungle in a chair for hour after hour, waiting for bat conversations to happen. She even brought along books to pass the time. Scientific research is not always riveting. KELLY: No. All told, Ahana Fernandez and her colleagues conducted their research for these last five years, and they found something else along the way. Baby bats babble. FERNANDEZ: They use sort of a vocal practice behavior which is reminiscent of babbling in infants. KELLY: Bat baby talk. PFEIFFER: Her team's report was published this month, and it shows that in the first three months of life, these bat pups experiment with their speech. FERNANDEZ: They learn a part of their adult vocal repertoire through vocal imitation as we humans do. © 2020 npr

Keyword: Animal Communication; Language
Link ID: 27444 - Posted: 09.02.2020

By Jane E. Brody Orthostatic hypotension — to many people those are unfamiliar words for a relatively common but often unrecognized medical problem that can have devastating consequences, especially for older adults. It refers to a brief but precipitous drop in blood pressure that causes lightheadedness or dizziness when standing up after lying down or sitting, and sometimes even after standing, for a prolonged period. The problem is likely to be familiar to people of all ages who may have been confined to bed for a long time by an injury, illness or surgery. It also often occurs during pregnancy. But middle-aged and older adults are most frequently affected. A significant number of falls and fractures, particularly among the elderly, are likely to result from orthostatic hypotension — literally, low blood pressure upon standing. Many an older person has fallen and broken a hip when getting out of bed in the morning or during the night to use the bathroom, precipitating a decline in health and loss of independence as a result of this blood pressure failure. Orthostatic hypotension is also a risk factor for strokes and heart attacks and even motor vehicle accidents. It can be an early warning sign of a serious underlying cardiovascular or neurological disorder, like a heart valve problem, the course of which might be altered if detected soon enough. But as one team of specialists noted, although orthostatic hypotension is a “highly prevalent” disorder, it is “frequently unrecognized until late in the clinical course.” Under normal circumstances, when we stand up, gravity temporarily causes blood to pool in the lower half of the body; then, within 20 or 30 seconds, receptors in the heart and carotid arteries in the neck trigger a compensating mechanism called the baroreflex that raises the heart rate and constricts blood vessels to increase blood pressure and provide the brain with an adequate supply of blood. © 2020 The New York Times Company

Keyword: Stress
Link ID: 27442 - Posted: 09.02.2020

By Carolyn Wilke Taste buds can turn food from mere fuel into a memorable meal. Now researchers have discovered a set of supersensing cells in the taste buds of mice that can detect four of the five flavors that the buds recognize. Bitter, sweet, sour and umami — these cells can catch them all. That’s a surprise because it’s commonly thought that taste cells are very specific, detecting just one or two flavors. Some known taste cells respond to only one compound, for instance, detecting sweet sucralose or bitter caffeine. But the new results suggest that a far more complicated process is at work. When neurophysiologist Debarghya Dutta Banik and colleagues turned off the sensing abilities of more specific taste cells in mice, the researchers were startled to find other cells responding to flavors. Pulling those cells out of the rodents’ taste buds and giving them a taste of several compounds revealed a group of cells that can sense multiple chemicals across different taste classes, the team reports August 13 in PLOS Genetics. “We never expected that any population of [taste] cells would respond to so many different compounds,” says Dutta Banik, of the Indiana University School of Medicine in Indianapolis. But taste cells don’t respond to flavors in insolation; the brain and the tongue work together as tastemakers (SN: 11/24/15). So the scientists monitored the brain to see if it received bitter, sweet or umami signals when mice lacked a key protein needed for these broadly tasting cells to relay information. Those observations revealed that without the protein, the brain didn’t get the flavor messages, which was also shown when mice slurped bitter solutions as though they were water even though the rodents hate bitter tastes, says Dutta Banik, who did the work at the University at Buffalo in New York. © Society for Science & the Public 2000–2020.

Keyword: Chemical Senses (Smell & Taste)
Link ID: 27419 - Posted: 08.15.2020

Ian Sample Science editor Scientists have unravelled the mysterious mechanism behind the armpit’s ability to produce the pungent smell of body odour. Researchers at the University of York traced the source of underarm odour to a particular enzyme in a certain microbe that lives in the human armpit. To prove the enzyme was the chemical culprit, the scientists transferred it to an innocent member of the underarm microbe community and noted – to their delight – that it too began to emanate bad smells. The work paves the way for more effective deodorants and antiperspirants, the scientists believe, and suggests that humans may have inherited the mephitic microbes from our ancient primate ancestors. “We’ve discovered how the odour is produced,” said Prof Gavin Thomas, a senior microbiologist on the team. “What we really want to understand now is why.” Humans do not produce the most pungent constituents of BO directly. The offending odours, known as thioalcohols, are released as a byproduct when microbes feast on other compounds they encounter on the skin. The York team previously discovered that most microbes on the skin cannot make thioalcohols. But further tests revealed that one armpit-dwelling species, Staphylococcus hominis, was a major contributor. The bacteria produce the fetid fumes when they consume an odourless compound called Cys-Gly-3M3SH, which is released by sweat glands in the armpit. Advertisement Humans come with two types of sweat glands. Eccrine glands cover the body and open directly onto the skin. They are an essential component of the body’s cooling system. Apocrine glands, on the other hand, open into hair follicles, and are crammed into particular places: the armpits, nipples and genitals. Their role is not so clear. © 2020 Guardian News & Media Limited

Keyword: Chemical Senses (Smell & Taste); Sexual Behavior
Link ID: 27390 - Posted: 07.29.2020

Edmund Chong When you experience something with your senses, it evokes complex patterns of activity in your brain. One important goal in neuroscience is to decipher how these neural patterns drive the sensory experience. For example, can the smell of chocolate be represented by a single brain cell, groups of cells firing all at the same time or cells firing in some precise symphony? The answers to these questions will lead to a broader understanding of how our brains represent the external world. They also have implications for treating disorders where the brain fails in representing the external world: for example, in the loss of sight of smell. To understand how the brain drives sensory experience, my colleagues and I focus on the sense of smell in mice. We directly control a mouse’s neural activity, generating “synthetic smells” in the olfactory part of its brain in order to learn more about how the sense of smell works. Our latest experiments discovered that scents are represented by very specific patterns of activity in the brain. Like the notes of a melody, the cells fire in a unique sequence with particular timing to represent the sensation of smelling a unique odor. Using mice to study smell is appealing to researchers because the relevant brain circuits have been mapped out, and modern tools allow us to directly manipulate these brain connections. © 2010–2020, The Conversation US, Inc.

Keyword: Chemical Senses (Smell & Taste)
Link ID: 27352 - Posted: 07.08.2020

By Bret Stetka How do humans and other animals distinguish between the smell of rotting seafood or the enticing allure of a ripe banana? New research at New York University Langone Health and their colleagues uses artificially created odors to help reveal the intricate chain of events that allow one odor to be distinguished from another. The results were published today in Science. In the deep recesses of the nose are millions of sensory neurons that, along with our eyes and ears, help conjure the world around us. When stimulated by a chemical with a smell, or an odorant, they send nerve impulses to thousands of clusters of neurons in the glomeruli, which make up the olfactory bulb, the brain’s smell center. Different patterns of glomerular activation are known to generate the sensation of specific odors. Firing one set of glomeruli elicits the perception of pineapples; firing another evokes pickles. Unlike other sensations, such as sight and hearing, scientists do not know which qualities of a particular smell are used by the brain to perceive it. When you see a person’s face, you may remember the eyes, which helps you recognize that individual in the future. But the ears and nose might be less important in how the brain represents that person. The authors of the new study sought to identify distinguishing features involved in forming the representation of odors in the brain. To do so, they used a technique called optogenetics to activate glomeruli in mice. Optogenetics uses light to stimulate specific neurons in the brain. And it can help determine the function of particular brain regions. © 2020 Scientific American

Keyword: Chemical Senses (Smell & Taste)
Link ID: 27315 - Posted: 06.22.2020

By Laura Sanders Scientists have implanted an artificial odor directly in the brains of mice. It doesn’t mean that mental Smell-O-Vision technology is coming soon. But the results, published June 18 in Science, deliver clues to how the brain processes information. Details about the synthetic smell may help answer “fundamental questions in olfaction,” says computational biologist Saket Navlakha of Cold Spring Harbor Laboratory in New York, who wasn’t involved in the study. Studies on the senses offer a window into how brains shape signals from the outside world into perceptions, and how those perceptions can guide behavior (SN: 7/18/19). To build artificial smells in mice’s brains, researchers used optogenetics, a technique in which light prods genetically engineered nerve cells to fire signals (SN: 1/15/10). Neuroscientist Dima Rinberg of New York University’s Grossman School of Medicine and colleagues targeted nerve cells in mice’s olfactory bulbs. There, clusters of nerve endings called glomeruli organize the smell signals picked up in the nose. Like playing a short ditty on a piano, Rinberg and colleagues activated nerve cells in six spots (each of which might include between one and three glomeruli) in a certain order. This neural melody was designed to be a simplified version of how a real odor might play those nerve cells. (It’s not known what the artificial odor actually smells like to a mouse.) © Society for Science & the Public 2000–2020.

Keyword: Chemical Senses (Smell & Taste)
Link ID: 27312 - Posted: 06.19.2020

By Laura Sanders The virus responsible for COVID-19 can steal a person’s sense of smell, leaving them noseblind to fresh-cut grass, a pungent meal or even their own stale clothes. But so far, details remain elusive about how SARS-CoV-2, the coronavirus that causes COVID-19, can infiltrate and shut down the body’s smelling machinery. One recent hint comes from a young radiographer who lost her sense of smell. She had signs of viral infection in her brain. Other studies, though, have not turned up signs of the virus in the brain. Contradictory evidence means that no one knows whether SARS-CoV-2 can infect nerve cells in the brain directly, and if so, whether the virus’s route to the brain can sometimes start in the nose. Understanding how people’s sense of smell is harmed (SN: 5/11/20), a symptom estimated to afflict anywhere between 20 and 80 percent of people with COVID-19, could reveal more about how the virus operates. One thing is certain so far, though: The virus can steal the sense of smell in a way that’s not normal. “There’s something unusual about the relationship between COVID-19 and smell,” says neuroscientist Sandeep Robert Datta of Harvard Medical School in Boston. Colds can prevent smelling by stuffing the nose up with mucus. But SARS-CoV-2 generally leaves the nose clear. “Lots of people are complaining about losing their sense of smell when they don’t feel stuffed up at all,” Datta says. © Society for Science & the Public 2000–2020.

Keyword: Chemical Senses (Smell & Taste)
Link ID: 27302 - Posted: 06.13.2020

­­Researchers at the National Institute of Neurological Disorders and Stroke (NINDS), a part of the National Institutes of Health, have identified a specific, front-line defense that limits the infection to the olfactory bulb and protects the neurons of the olfactory bulb from damage due to the infection. Neurons in the nose respond to inhaled odors and send this information to a region of the brain referred to as the olfactory bulb. Although the location of nasal neurons and their exposure to the outside environment make them an easy target for infection by airborne viruses, viral respiratory infections rarely make their way from the olfactory bulb to the rest of the brain, where they could cause potentially fatal encephalitis. The study was published in Science Immunology. Taking advantage of special viruses that can be tracked with fluorescent microscopy, the researchers led by Dorian McGavern, Ph.D., senior investigator at NINDS, found that a viral infection that started in the nose was halted right before it could spread from the olfactory bulb to the rest of the central nervous system. “Airborne viruses challenge our immune system all the time, but rarely do we see viral infections leading to neurological conditions,” said Dr. McGavern. “This means that the immune system within this area has to be remarkably good at protecting the brain.” Additional experiments showed that microglia, immune cells within the central nervous system, took on an underappreciated role of helping the immune system recognize the virus and did so in a way that limited the damage to neurons themselves. This sparing of neurons is critical, because unlike cells in most other tissues, most neuronal populations do not come back.

Keyword: Chemical Senses (Smell & Taste); Glia
Link ID: 27287 - Posted: 06.06.2020

By Robert Martone When a concert opens with a refrain from your favorite song, you are swept up in the music, happily tapping to the beat and swaying with the melody. All around you, people revel in the same familiar music. You can see that many of them are singing, the lights flashing to the rhythm, while other fans are clapping in time. Some wave their arms over their head, and others dance in place. The performers and audience seem to be moving as one, as synchronized to one another as the light show is to the beat. A new paper in the journal NeuroImage has shown that this synchrony can be seen in the brain activities of the audience and performer. And the greater the degree of synchrony, the study found, the more the audience enjoys the performance. This result offers insight into the nature of musical exchanges and demonstrates that the musical experience runs deep: we dance and feel the same emotions together, and our neurons fire together as well. In the study, a violinist performed brief excerpts from a dozen different compositions, which were videotaped and later played back to a listener. Researchers tracked changes in local brain activity by measuring levels of oxygenated blood. (More oxygen suggests greater activity, because the body works to keep active neurons supplied with it.) Musical performances caused increases in oxygenated blood flow to areas of the brain related to understanding patterns, interpersonal intentions and expression. Data for the musician, collected during a performance, was compared to those for the listener during playback. In all, there were 12 selections of familiar musical works, including “Edelweiss,” Franz Schubert’s “Ave Maria,” “Auld Lang Syne” and Ludwig van Beethoven’s “Ode to Joy.” The brain activities of 16 listeners were compared to that of a single violinist. © 2020 Scientific American,

Keyword: Hearing
Link ID: 27277 - Posted: 06.03.2020