Chapter 6. Hearing, Balance, Taste, and Smell

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By Erin Garcia de Jesús For many people, one of the fastest tip-offs that they have COVID-19 is the loss of taste or smell. Now researchers have pinpointed some genetic variants in people that may make it more likely that the coronavirus might rob them of these senses. A study of nearly 70,000 adults with COVID-19 found that individuals with certain genetic tweaks on chromosome 4 were 11 percent more likely to lose the ability to smell or taste than people without the changes, researchers report January 17 in Nature Genetics. The data come from people who’d had their DNA analyzed by genetic testing company 23andMe and self-reported a case of COVID-19. Two genes, UGT2A1 and UGT2A2, that help people smell reside in the region of chromosome 4 linked to sensory loss during infection, epidemiologist Janie Shelton of 23andMe and colleagues found. Both genes make enzymes that metabolize substances called odorants, which produce distinctive smells. Sign up for e-mail updates on the latest coronavirus news and research Studies suggest that loss of smell, a hallmark symptom of COVID-19, stems from infections taking hold in smell-supporting cells called sustentacular cells (SN: 6/12/20). It’s possible that the genetic variants near UGT2A1 and UGT2A2 could affect how the two genes are turned on or off to somehow mess with smell during an infection, Shelton says. © Society for Science & the Public 2000–2022.

Keyword: Chemical Senses (Smell & Taste)
Link ID: 28160 - Posted: 01.19.2022

By Winston Choi-Schagrin SOUTH ST. PAUL, Minn. — Chuck McGinley, a chemical engineer, stepped out of his car, eyed the smokestack of an animal processing plant rising above the treetops, and inhaled deeply. At first he smelled nothing except the faint, sweet fragrance of the nearby trees. Suddenly, the wind picked up. “We have an oh-my-God smell!” Mr. McGinley exclaimed. Immediately one of his colleagues pressed a Nasal Ranger to his nose. The 14-inch-long smell-measuring device, which looks like a cross between a radar gun and a bugle, is one of Mr. McGinley’s most significant inventions. Using terms from one of Mr. McGinley’s other standard tools, an odor wheel, a chart akin to an artist’s color wheel that he has been fine-tuning for decades, the team described the stink. “Sour,” one person said. “Decay, with possibly some petroleum,” said another. Then, as quickly as it had arrived, the smell disappeared. “The wind decided it was going to gift us only a short sniff,” Mr. McGinley said. “To tease us.” Intuitively, humans know to avoid bad smells. Yet for a half-century, Mr. McGinley, 76, has returned again and again to society’s stinkiest sites, places very much like this one, in order to measure, describe and demystify smell. Climate Fwd There’s an ongoing crisis — and tons of news. Our newsletter keeps you up to date. Get it sent to your inbox. From his unconventional lab in a Minnesota suburb (it actually feels more like a ski lodge) Mr. McGinley and his son Mike have established an outsize influence over the measurement and understanding of odor. They have equipped scientists around the world with tools the elder Mr. McGinley invented, advised governments on odor regulations and empowered communities near smelly places to find a vocabulary for their complaints and a way to measure what their noses are telling them. In many ways, the growing demand for Mr. McGinley’s services and instruments signals society’s heightened awareness of the power of odor and its potential to make people physically ill or diminish their quality of life. His inventions have taken on a powerful role in a movement to recognize odor as a pollutant, not merely an annoyance, worthy of closer study and perhaps tighter regulation. © 2022 The New York Times Company

Keyword: Chemical Senses (Smell & Taste)
Link ID: 28153 - Posted: 01.15.2022

By Judith Graham The reports from coronavirus patients are disconcerting. Only a few hours before, they were enjoying a cup of pungent coffee or the fragrance of flowers in a garden. Then, as if a switch had been flipped, those smells disappeared. F Young and old alike are affected — more than 80 to 90 percent of those diagnosed with the virus, according to some estimates. While most people recover in a few months, 16 percent take half a year or longer to do so, research has found. According to new estimates, up to 1.6 million Americans have chronic smell problems because of covid-19, the disease caused by the coronavirus. Seniors are especially vulnerable, experts say. “We know that many older adults have a compromised sense of smell to begin with. Add to that the insult of covid, and it made these problems worse,” said Jayant Pinto, a professor of surgery and a specialist in sinus and nasal diseases at the University of Chicago Medical Center. Advertisement Recent data highlights the interaction between covid-19, advanced age and loss of smell. When Italian researchers evaluated 101 patients who had been hospitalized for mild to moderate covid-19, 50 showed objective signs of smell impairment six months later. Those 65 or older were nearly twice as likely to be impaired; those 75 or older were more than 2½ times as likely. Most people aren’t aware of the extent to which smell can be diminished in later life. More than half of 65-to-80-year-olds have some degree of smell loss, or olfactory dysfunction, as it’s known in the scientific literature. That rises to as high as 80 percent for those even older. People affected often report concerns about safety, less enjoyment eating and an impaired quality of life. But because the ability to detect, identify and discriminate among odors declines gradually, most older adults — up to 75 percent of those with some degree of smell loss — don’t realize they’re affected.

Keyword: Chemical Senses (Smell & Taste)
Link ID: 28151 - Posted: 01.12.2022

Stephen Wooding The sweetness of sugar is one of life’s great pleasures. People’s love for sweet is so visceral, food companies lure consumers to their products by adding sugar to almost everything they make: yogurt, ketchup, fruit snacks, breakfast cereals and even supposed health foods like granola bars. Schoolchildren learn as early as kindergarten that sweet treats belong in the smallest tip of the food pyramid, and adults learn from the media about sugar’s role in unwanted weight gain. It’s hard to imagine a greater disconnect between a powerful attraction to something and a rational disdain for it. How did people end up in this predicament? I’m an anthropologist who studies the evolution of taste perception. I believe insights into our species’ evolutionary history can provide important clues about why it’s so hard to say no to sweet. The basic activities of day-to-day life, such as raising the young, finding shelter and securing enough food, all required energy in the form of calories. Individuals more proficient at garnering calories tended to be more successful at all these tasks. They survived longer and had more surviving children – they had greater fitness, in evolutionary terms. One contributor to success was how good they were at foraging. Being able to detect sweet things – sugars – could give someone a big leg up. In nature, sweetness signals the presence of sugars, an excellent source of calories. So foragers able to perceive sweetness could detect whether sugar was present in potential foods, especially plants, and how much. © 2010–2022, The Conversation US, Inc.

Keyword: Chemical Senses (Smell & Taste); Evolution
Link ID: 28146 - Posted: 01.12.2022

By Elizabeth Landau In a narrow medical school hallway, Matt Stewart opened a large cabinet to reveal dozens of shelves stacked with wooden boxes and trays, some at least 100 years old. Stewart, tall and silver-haired, pulled out one of the trays and showed off its contents: Thin slices of human skull bones and the organs of hearing and balance they contain, stained shades of pink. Affixed to microscope slides, the anatomical bits resembled abstract rubber stamp art, no bigger than thumbprints. “Our Johns Hopkins history,” he said, referring to the university’s collection of specimens from more than 5,000 patients. Stewart’s research team at Johns Hopkins University in Baltimore had a long, complicated journey to make slides like these in 2021. The researchers need these specimens, sliced from the portion of skull that houses the inner ear, to ask a fundamental question about the novel coronavirus, SARS-CoV-2: Does it directly invade the cells of tissues that enable hearing and balance? Ear surgeon Matt Stewart leads a research team at Johns Hopkins University that is investigating how SARS-CoV-2 might infect ear cells that enable hearing and balance. Data on ear problems as they relate to Covid-19, the disease caused by SARS-CoV-2, is spotty. To date, case reports and small studies have found that some Covid-19 patients experience significant and rapid hearing loss, ringing in the ears called tinnitus, or balance issues. Estimates vary on the prevalence of these symptoms, but because the coronavirus has infected hundreds of millions of people, even a few percent of Covid patients experiencing hearing loss would add up to a large increase globally. Yet no causal link has been drawn between the novel coronavirus and auditory symptoms. Hearing problems aren’t even on lists of Covid-19 symptoms, short or long-term, published by the Centers for Disease Control and Prevention.

Keyword: Hearing
Link ID: 28139 - Posted: 01.05.2022

By Ariana Remmel Scientists have finally sniffed out the molecules behind marijuana’s skunky aroma. The heady bouquet that wafts off of fresh weed is actually a cocktail of hundreds of fragrant compounds. The most prominent floral, citrusy and piney overtones come from a common class of molecules called terpenes, says analytical chemist Iain Oswald of Abstrax Tech, a private company in Tustin, Calif., that develops terpenes for cannabis products (SN: 4/30/18). But the source of that funky ganja note has been hard to pin down. Now, an analysis is the first to identify a group of sulfur compounds in cannabis that account for the skunklike scent, researchers report November 12 in ACS Omega. Oswald and colleagues had a hunch that the culprit may contain sulfur, a stinky element found in hops and skunk spray. So the team started by rating the skunk factor of flowers harvested from more than a dozen varieties of Cannabis sativa on a scale from zero to 10, with 10 being the most pungent. Next, the team created a “chemical fingerprint” of the airborne components that contributed to each cultivar’s unique scent using gas chromatography, mass spectroscopy and a sulfur chemiluminescence detector. As suspected, the researchers found small amounts of several fragrant sulfur compounds lurking in the olfactory profiles of the smelliest cultivars. The most dominant was a molecule called prenylthiol, or 3-methyl-2-butene-1-thiol, that gives “skunked beer” its notorious flavor (SN: 11/27/05). © Society for Science & the Public 2000–2021

Keyword: Chemical Senses (Smell & Taste); Drug Abuse
Link ID: 28092 - Posted: 12.01.2021

ByEmily Underwood Scientists have argued for decades over whether humans have pheromones, chemical compounds that trigger aggression and mating in insects and other animals. Although the notion has great popular appeal—search Amazon for “pheromone” and you’ll get the idea—there’s scant evidence for this kind of signal in our species. A new study could change that. Researchers have identified an odorless compound emitted by people—and in particular babies—called hexadecanal, or HEX, that appears to foster aggressive behavior in women and blunt it in men. “We cannot say that this is a pheromone,” says study author Noam Sobel, a neuroscientist at the Weizmann Institute of Science. “But we can say that it’s a molecule expressed by the human body that influences human behavior, specifically aggressive behavior, in a predicted manner.” Humans emit HEX from their skin, saliva, and feces, and it’s among the most abundant molecules babies emit from their heads. When researchers isolated the odorless compound and piped it into mouse cages, it had a relaxing effect on the animals, says Sobel, who studies the role of scent in human interactions. To test how HEX affects people, Eva Mishor, who earned her Ph.D. in Sobel’s lab, created a series of computer games designed to evoke intense frustration—and a measurable response to it—in 126 human participants. Half of the volunteers wore a HEX-infused adhesive strip on their upper lips while they played, whereas the other half wore strips that smelled identical but were HEX-free. In one task, participants negotiated with an unseen partner to divvy up a sum of virtual money. The participants thought they were playing with another person, but they were actually playing against computers. If a player offered their “partner” anything less than 90% of the whole amount, the computer rejected their proposals with a bright red “NO!” preventing them from earning any money. © 2021 American Association for the Advancement of Science.

Keyword: Chemical Senses (Smell & Taste); Aggression
Link ID: 28086 - Posted: 11.20.2021

Jon Hamilton Headaches, nausea, dizziness, and confusion are among the most common symptoms of a concussion. But researchers say a blow to the head can also make it hard to understand speech in a noisy room. "Making sense of sound is one of the hardest jobs that we ask our brains to do," says Nina Kraus, a professor of neurobiology at Northwestern University. "So you can imagine that a concussion, getting hit in the head, really does disrupt sound processing." About 15% to 20% of concussions cause persistent sound-processing difficulties, Kraus says, which suggests that hundreds of thousands of people are affected each year in the U.S. The problem is even more common in the military, where many of the troops who saw combat in Iraq and Afghanistan sustained concussions from roadside bombs. From ear to brain Our perception of sound starts with nerve cells in the inner ear that transform pressure waves into electrical signals, Kraus says. But it takes a lot of brain power to transform those signals into the auditory world we perceive. Article continues after sponsor message The brain needs to compare the signals from two ears to determine the source of a sound. Then it needs to keep track of changes in volume, pitch, timing and other characteristics. Kraus's lab, called Brainvolts, is conducting a five-year study of 500 elite college athletes to learn how a concussion can affect the brain's ability to process the huge amount of auditory information it receives. And she devotes an entire chapter to concussion in her 2021 book, Of Sound Mind: How Our Brain Constructs a Meaningful Sonic World. © 2021 npr

Keyword: Brain Injury/Concussion; Hearing
Link ID: 28064 - Posted: 11.06.2021

Jordana Cepelewicz Hearing is so effortless for most of us that it’s often difficult to comprehend how much information the brain’s auditory system needs to process and disentangle. It has to take incoming sounds and transform them into the acoustic objects that we perceive: a friend’s voice, a dog barking, the pitter-patter of rain. It has to extricate relevant sounds from background noise. It has to determine that a word spoken by two different people has the same linguistic meaning, while also distinguishing between those voices and assessing them for pitch, tone and other qualities. According to traditional models of neural processing, when we hear sounds, our auditory system extracts simple features from them that then get combined into increasingly complex and abstract representations. This process allows the brain to turn the sound of someone speaking, for instance, into phonemes, then syllables, and eventually words. But in a paper published in Cell in August, a team of researchers challenged that model, reporting instead that the auditory system often processes sound and speech simultaneously and in parallel. The findings suggest that how the brain makes sense of speech diverges dramatically from scientists’ expectations, with the signals from the ear branching into distinct brain pathways at a surprisingly early stage in processing — sometimes even bypassing a brain region thought to be a crucial stepping-stone in building representations of complex sounds.

Keyword: Language; Hearing
Link ID: 28058 - Posted: 10.30.2021

Bill Chappell People with mild or moderate hearing loss could soon be able to buy hearing aids without a medical exam or special fitting, under a new rule being proposed by the Food and Drug Administration. The agency says 37.5 million American adults have difficulty hearing. "Today's move by FDA takes us one step closer to the goal of making hearing aids more accessible and affordable for the tens of millions of people who experience mild to moderate hearing loss," Health and Human Services Secretary Xavier Becerra said as he announced the proposed rule on Tuesday. There is no timeline yet for when consumers might be able to buy an FDA-regulated over-the-counter (OTC) hearing aid. The proposed rule is now up for 90 days of public comment. The Hearing Loss Association of America, a consumer advocacy group, welcomed the proposal. "This is one step closer to seeing OTC hearing devices on the market," Barbara Kelley, the group's executive director, said in an email to NPR. "We hope adults will be encouraged to take that important first step toward good hearing health." Advocates and lawmakers have been calling for OTC hearing aids for years, including in a big push in 2017, when Sen. Elizabeth Warren, D-Mass., and co-sponsor Sen. Chuck Grassley, R-Iowa, introduced the bipartisan Over-the-Counter Hearing Aid Act. The legislators are now praising the FDA's move. © 2021 npr

Keyword: Hearing
Link ID: 28042 - Posted: 10.20.2021

Abby Olena Most people enjoy umami flavor, which is perceived when a taste receptor called T1R1/T1R3 senses the amino acid glutamate. In some other mammals, such as mice, however, this same receptor is much less sensitive to glutamate. In a new study published August 26 in Current Biology, researchers uncover the molecular basis for this difference. They show that the receptor evolved in humans and some other primates away from mostly binding free nucleotides, which are common in insects, to preferentially binding glutamate, which is abundant in leaves. The authors argue that the change facilitated a major evolutionary shift in these primates toward a plant-heavy diet. “The question always comes up about the evolution of umami taste: In humans, our receptor is narrowly tuned to glutamate, and we never had a good answer for why,” says Maude Baldwin, a sensory biologist at the Max Planck Institute for Ornithology in Germany. She was not involved in the new work, but coauthored a 2014 study with Yasuka Toda, who is also a coauthor on the new paper, showing that the T1R1/T1R3 receptor is responsible for sweet taste in hummingbirds. In the new study, the authors find “that this narrow tuning has evolved convergently multiple times [and] that it’s related to folivory,” she says, calling the paper “a hallmark, fantastic study, and one that will become a textbook example of how taste evolution can relate to diet and how to address these types of questions in a rigorous, comprehensive manner.” © 1986–2021 The Scientist.

Keyword: Chemical Senses (Smell & Taste); Evolution
Link ID: 28037 - Posted: 10.16.2021

Abby Olena Most people enjoy umami flavor, which is perceived when a taste receptor called T1R1/T1R3 senses the amino acid glutamate. In some other mammals, such as mice, however, this same receptor is much less sensitive to glutamate. In a new study published August 26 in Current Biology, researchers uncover the molecular basis for this difference. They show that the receptor evolved in humans and some other primates away from mostly binding free nucleotides, which are common in insects, to preferentially binding glutamate, which is abundant in leaves. The authors argue that the change facilitated a major evolutionary shift in these primates toward a plant-heavy diet. “The question always comes up about the evolution of umami taste: In humans, our receptor is narrowly tuned to glutamate, and we never had a good answer for why,” says Maude Baldwin, a sensory biologist at the Max Planck Institute for Ornithology in Germany. She was not involved in the new work, but coauthored a 2014 study with Yasuka Toda, who is also a coauthor on the new paper, showing that the T1R1/T1R3 receptor is responsible for sweet taste in hummingbirds. In the new study, the authors find “that this narrow tuning has evolved convergently multiple times [and] that it’s related to folivory,” she says, calling the paper “a hallmark, fantastic study, and one that will become a textbook example of how taste evolution can relate to diet and how to address these types of questions in a rigorous, comprehensive manner.” In 2011, Toda, who was then at the University of Tokyo and now leads a group at Meiji University in Japan, and Takumi Misaka of the University of Tokyo developed a strategy to use cultured cells to analyze the function of taste receptors. They used the technique to tease out the parts of the human T1R1/T1R3 that differed from that of mice and thus underlie the high glutamate sensitivity in the human receptor, work that they published in 2013. © 1986–2021 The Scientist.

Keyword: Chemical Senses (Smell & Taste); Evolution
Link ID: 27986 - Posted: 09.13.2021

By Jonathan Lambert At least 65 million years of evolution separate humans and greater sac-winged bats, but these two mammals share a key feature of learning how to speak: babbling. Just as human infants babble their way from “da-da-da-da” to “Dad,” wild bat pups (Saccopteryx bilineata) learn the mating and territorial songs of adults by first babbling out the fundamental syllables of the vocalizations, researchers report in the Aug. 20 Science. These bats now join humans as the only clear examples of mammals who learn to make complex vocalizations through babbling. “This is a hugely important step forward in the study of vocal learning,” says Tecumseh Fitch, an evolutionary biologist at the University of Vienna not involved in the new study. “These findings suggest that there are deep parallels between how humans and young bats learn to control their vocal apparatus,” he says. The work could enable future studies that might allow researchers to peer deeper into the brain activity that underpins vocal learning. Before complex vocalizations, whether words or mating songs, can be spoken or sung, vocalizers must learn to articulate the syllables that make up a species’s vocabulary, says Ahana Fernandez, an animal behavior biologist at the Museum für Naturkunde in Berlin. “Babbling is a way of practicing,” and honing those vocalizations, she says. The rhythmic, repetitive “ba-ba-ba’s” and “ga-ga-ga’s” of human infants may sound like gibberish, but they are necessary exploratory steps toward learning how to talk. Seeing whether babbling is required for any animal that learns complex vocalizations necessitates looking in other species. © Society for Science & the Public 2000–2021.

Keyword: Language; Hearing
Link ID: 27957 - Posted: 08.21.2021

Michael Marshall Since the beginning of the pandemic, researchers have been trying to understand how the coronavirus SARS-CoV-2 affects the brain.Credit: Stanislav Krasilnikov/TASS/Getty How COVID-19 damages the brain is becoming clearer. New evidence suggests that the coronavirus’s assault on the brain could be multipronged: it might attack certain brain cells directly, reduce blood flow to brain tissue or trigger production of immune molecules that can harm brain cells. Infection with the coronavirus SARS-CoV-2 can cause memory loss, strokes and other effects on the brain. The question, says Serena Spudich, a neurologist at Yale University in New Haven, Connecticut, is: “Can we intervene early to address these abnormalities so that people don’t have long-term problems?” With so many people affected — neurological symptoms appeared in 80% of the people hospitalized with COVID-19 who were surveyed in one study1 — researchers hope that the growing evidence base will point the way to better treatments. Breaking into the brain SARS-CoV-2 can have severe effects: a preprint posted last month2 compared images of people’s brains from before and after they had COVID-19, and found loss of grey matter in several areas of the cerebral cortex. (Preprints are published without peer review.) Early in the pandemic, researchers speculated that the virus might cause damage by somehow entering the brain and infecting neurons, the cells responsible for transmitting and processing information. But studies have since indicated3 that the virus has difficulty getting past the brain’s defence system — the blood–brain barrier — and that it doesn’t necessarily attack neurons in any significant way.

Keyword: Chemical Senses (Smell & Taste); Learning & Memory
Link ID: 27899 - Posted: 07.08.2021

By Elizabeth Pennisi Almost 200 years ago, the renowned U.S. naturalist John James Audubon hid a decaying pig carcass under a pile of brush to test vultures’ sense of smell. When the birds overlooked the pig—while one flocked to a nearly odorless stuffed deer skin—he took it as proof that they rely on vision, not smell, to find their food. His experiment cemented a commonly held idea. Despite later evidence that vultures and a few specialized avian hunters use odors after all, the dogma that most birds aren’t attuned to smell endured. Now, that dogma is being eroded by findings on birds’ behavior and molecular hardware, two of which were published just last month. One showed storks home in on the smell of freshly mowed grass; another documented scores of functional olfactory receptors in multiple bird species. Researchers are realizing, says evolutionary biologist Scott Edwards of Harvard University, that “olfaction has a lot of impact on different aspects of bird biology.” Forty years ago, when ethologist Floriano Papi proposed that homing pigeons find their way back to a roost by sniffing out its chemical signature, his colleagues scoffed at the idea. They pointed out that birds have several other keen senses to guide them, including sight and, in the case of pigeons and some other species, a magnetic sense. “By then, biological textbooks already stated unequivocally that birds have little to no sense of smell, and many people still believe it—even scientists,” says Danielle Whittaker, a chemical ecologist at Michigan State University. © 2021 American Association for the Advancement of Science.

Keyword: Chemical Senses (Smell & Taste); Evolution
Link ID: 27897 - Posted: 07.08.2021

Allison Aubrey Imagine a sound that travels with you no matter where you go. Whether it's a ring, a whoosh or a crickets-like buzz, you can't escape it. "Mine was like this high-pitched sonic sound," says Elizabeth Fraser, who developed tinnitus last fall. It came on suddenly at a time when many people delayed doctor visits due to the coronavirus pandemic. "It just felt like an invasion in my head, so I was really distressed," Fraser recalls. Tinnitus is the perception of ringing when, in fact, no external sound is being produced. "You can equate it to a phantom sound," explains Sarah Sydlowski, a doctor of audiology at Cleveland Clinic. The Centers for Disease Control and Prevention estimates that 20 million Americans have chronic tinnitus. And studies show the pandemic ushered in both new cases and a worsening of the condition among people who already had it. The British Tinnitus Association reported a surge in the number of people accessing its services, including a 256% increase in the number of web chats amid the pandemic. Elizabeth Fraser started hearing a "high-pitched sonic sound" in her ears last fall. It came on suddenly at a time when many people delayed doctor visits due to the coronavirus pandemic. "It just felt like an invasion in my head, so I was really distressed," Fraser recalls. © 2021 npr

Keyword: Hearing
Link ID: 27877 - Posted: 06.26.2021

Kurt Schwenk As dinosaurs lumbered through the humid cycad forests of ancient South America 180 million years ago, primeval lizards scurried, unnoticed, beneath their feet. Perhaps to avoid being trampled by their giant kin, some of these early lizards sought refuge underground. Here they evolved long, slender bodies and reduced limbs to negotiate the narrow nooks and crevices beneath the surface. Without light, their vision faded, but to take its place, an especially acute sense of smell evolved. It was during this period that these proto-snakes evolved one of their most iconic traits – a long, flicking, forked tongue. These reptiles eventually returned to the surface, but it wasn’t until the extinction of dinosaurs many millions of years later that they diversified into myriad types of modern snakes. As an evolutionary biologist, I am fascinated by these bizarre tongues – and the role they have played in snakes’ success. Snake tongues are so peculiar they have fascinated naturalists for centuries. Aristotle believed the forked tips provided snakes a “twofold pleasure” from taste – a view mirrored centuries later by French naturalist Bernard Germain de Lacépède, who suggested the twin tips could adhere more closely to “the tasty body” of the soon-to-be snack. A 17th-century astronomer and naturalist, Giovanni Battista Hodierna, thought snakes used their tongues for “picking the dirt out of their noses … since they are always grovelling on the ground.” Others contended the tongue captured flies “with wonderful nimbleness … betwixt the forks,” or gathered air for sustenance.

Keyword: Chemical Senses (Smell & Taste); Evolution
Link ID: 27876 - Posted: 06.26.2021

Jordana Cepelewicz Smell, rather than sight, reigns as the supreme sense for most animals. It allows them to find food, avoid danger and attract mates; it dominates their perceptions and guides their behavior; it dictates how they interpret and respond to the deluge of sensory information all around them. “How we as biological creatures interface with chemistry in the world is profoundly important for understanding who we are and how we navigate the universe,” said Bob Datta, a neurobiologist at Harvard Medical School. Yet olfaction might also be the least well understood of our senses, in part because of the complexity of the inputs it must reckon with. What we might label as a single odor — the smell of coffee in the morning, of wet grass after a summer storm, of shampoo or perfume — is often a mixture of hundreds of types of chemicals. For an animal to detect and discriminate between the many scents that are key to its survival, the limited repertoire of receptors on its olfactory sensory neurons must somehow recognize a vast number of compounds. So an individual receptor has to be able to respond to many diverse, seemingly unrelated odor molecules. That versatility is at odds with the traditional lock-and-key model governing how selective chemical interactions tend to work. “In high school biology, that’s what I learned about ligand-receptor interactions,” said Annika Barber, a molecular biologist at Rutgers University. “Something has to fit precisely in a site, and then it changes the [protein’s atomic arrangement], and then it works.” All Rights Reserved © 2021

Keyword: Chemical Senses (Smell & Taste)
Link ID: 27869 - Posted: 06.23.2021

By Deborah Schoch Marcel Kuttab first sensed something was awry while brushing her teeth a year ago, several months after recovering from Covid-19. Her toothbrush tasted dirty, so she threw it out and got a new one. Then she realized the toothpaste was at fault. Onions and garlic and meat tasted putrid, and coffee smelled like gasoline — all symptoms of the once little-known condition called parosmia that distorts the senses of smell and taste. Dr. Kuttab, 28, who has a pharmacy doctoral degree and works for a drug company in Massachusetts, experimented to figure out what foods she could tolerate. “You can spend a lot of money in grocery stores and land up not using any of it,” she said. The pandemic has put a spotlight on parosmia, spurring research and a host of articles in medical journals. Membership has swelled in existing support groups, and new ones have sprouted. A fast-growing British-based Facebook parosmia group has more than 14,000 members. And parosmia-related ventures are gaining followers, from podcasts to smell training kits. Yet a key question remains unanswered: How long does Covid-linked parosmia last? Scientists have no firm timelines. Of five patients interviewed for this article, all of whom first developed parosmia symptoms in late spring and early summer of last year, none has fully regained normal smell and taste. Brooke Viegut, whose parosmia began in May 2020, worked for an entertainment firm in New York City before theaters were shuttered. She believes she caught Covid in March during a quick business trip to London, and, like many other patients, she lost her sense of smell. Before she regained it completely, parosmia set in, and she could not tolerate garlic, onions or meat. Even broccoli, she said at one point earlier this year, had a chemical smell. She still can’t stomach some foods, but she is growing more optimistic. “A lot of fruits taste more like fruit now instead of soap,” she said. And she recently took a trip without getting seriously nauseous. “So, I’d say that’s progress.” © 2021 The New York Times Company

Keyword: Chemical Senses (Smell & Taste); Neuroimmunology
Link ID: 27857 - Posted: 06.16.2021

Ed Yong Carl Schoonover and Andrew Fink are confused. As neuroscientists, they know that the brain must be flexible but not too flexible. It must rewire itself in the face of new experiences, but must also consistently represent the features of the external world. How? The relatively simple explanation found in neuroscience textbooks is that specific groups of neurons reliably fire when their owner smells a rose, sees a sunset, or hears a bell. These representations—these patterns of neural firing—presumably stay the same from one moment to the next. But as Schoonover, Fink, and others have found, they sometimes don’t. They change—and to a confusing and unexpected extent. Schoonover, Fink, and their colleagues from Columbia University allowed mice to sniff the same odors over several days and weeks, and recorded the activity of neurons in the rodents’ piriform cortex—a brain region involved in identifying smells. At a given moment, each odor caused a distinctive group of neurons in this region to fire. But as time went on, the makeup of these groups slowly changed. Some neurons stopped responding to the smells; others started. After a month, each group was almost completely different. Put it this way: The neurons that represented the smell of an apple in May and those that represented the same smell in June were as different from each other as those that represent the smells of apples and grass at any one time. This is, of course, just one study, of one brain region, in mice. But other scientists have shown that the same phenomenon, called representational drift, occurs in a variety of brain regions besides the piriform cortex. Its existence is clear; everything else is a mystery. Schoonover and Fink told me that they don’t know why it happens, what it means, how the brain copes, or how much of the brain behaves in this way. How can animals possibly make any lasting sense of the world if their neural responses to that world are constantly in flux? (c) 2021 by The Atlantic Monthly Group

Keyword: Chemical Senses (Smell & Taste)
Link ID: 27852 - Posted: 06.11.2021