Chapter 9. Hearing, Balance, Taste, and Smell

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By Lisa Sanders, M.D. “We were thinking about going bowling with the kids tomorrow,” the woman told her 43-year-old brother as they settled into their accustomed spots in the living room of their mother’s home in Chicago. It was late — nearly midnight — and he had arrived from Michigan to spend the days between Christmas and New Year’s with this part of his family. She and her husband and her brother grew up together and spent many late nights laughing and talking. She knew her brother was passionate about bowling. He had spent almost every day in his local alley two summers ago. So she was taken by surprise when he answered, “I can’t do that anymore.” Certainly, her brother had had a tough year. It seemed to start with his terrible heartburn. For most of his life, he had what he described as run-of-the-mill heartburn, usually triggered by eating late at night, and he would have to take a couple of antacid tablets. But that year his heartburn went ballistic. His mouth always tasted like metal. And the reflux of food back up the esophagus would get so bad that it would make him vomit. Nothing seemed to help. He quit drinking coffee. Quit drinking alcohol. Stopped eating spicy foods. He told his doctor, who started him on a medication known as a proton pump inhibitor (P.P.I.) to reduce the acid or excess protons his stomach made. That pill provided relief from the burning pain. But he still had the metallic taste in his mouth, still felt sick after eating. He still vomited several times a week. When he discovered that he wouldn’t throw up when he drank smoothies, he almost completely gave up solid foods. When he was still feeling awful after weeks on the P.P.I., his gastroenterologist used a tiny camera to take a look at his esophagus. His stomach looked fine, but the region where the esophagus entered the stomach was a mess. Normally the swallowing tube ends with a tight sphincter that stays closed to protect delicate tissue from the harsh acid of the stomach. It opens when swallowing, to let the food pass. But his swallowing tube was wide open and the tissue around the sphincter was red and swollen. © 2024 The New York Times Company

Keyword: Hearing
Link ID: 29137 - Posted: 02.08.2024

By Gina Kolata Aissam Dam, an 11-year-old boy, grew up in a world of profound silence. He was born deaf and had never heard anything. While living in a poor community in Morocco, he expressed himself with a sign language he invented and had no schooling. Last year, after moving to Spain, his family took him to a hearing specialist, who made a surprising suggestion: Aissam might be eligible for a clinical trial using gene therapy. On Oct. 4, Aissam was treated at the Children’s Hospital of Philadelphia, becoming the first person to get gene therapy in the United States for congenital deafness. The goal was to provide him with hearing, but the researchers had no idea if the treatment would work or, if it did, how much he would hear. The treatment was a success, introducing a child who had known nothing of sound to a new world. “There’s no sound I don’t like,” Aissam said, with the help of interpreters during an interview last week. “They’re all good.” While hundreds of millions of people in the world live with hearing loss that is defined as disabling, Aissam is among those whose deafness is congenital. His is an extremely rare form, caused by a mutation in a single gene, otoferlin. Otoferlin deafness affects about 200,000 people worldwide. The goal of the gene therapy is to replace the mutated otoferlin gene in patients’ ears with a functional gene. Although it will take years for doctors to sign up many more patients — and younger ones — to further test the therapy, researchers said that success for patients like Aissam could lead to gene therapies that target other forms of congenital deafness. © 2024 The New York Times Company

Keyword: Hearing
Link ID: 29119 - Posted: 01.27.2024

By Shaena Montanari Around 2012, Jennifer Groh and her colleagues began a series of experiments investigating the effect of eye movements on auditory signals in the brain. It wasn’t until years later that they noticed something curious in their data: In both an animal model and in people, eye movements coincide with ripples across the eardrum. The finding, published in 2018, seemed “weird,” says Groh, professor of psychology and neuroscience at Duke University — and ripe for further investigation. “You can go your whole career never studying something that is anywhere near as beautifully regular and reproducible,” she says. “Signals that are really robust are unlikely to be just random.” A new experiment from Groh’s lab has now taken her observation a step further and suggests the faint sounds — dubbed “eye movement-related eardrum oscillations,” or EMREOs for short — serve to link two sensory systems. The eardrum oscillations contain “clean and precise” information about the direction of eye movements and, according to Groh’s working hypothesis, help animals connect sound with a visual scene. “The basic problem is that the way we localize visual information and the way we localize sounds leads to two different reference frames,” Groh says. EMREOs, she adds, play a part in relating those frames. The brain, and not the eyes, must generate the oscillations, Groh and her colleagues say, because they happen at the same time as eye movements, or sometimes even before. To learn more about the oscillations, the team placed small microphones in the ears of 10 volunteers, who then performed visual tasks while the researchers tracked their eye movements. The group published their results in Proceedings of the National Academy of Sciences in November. © 2024 Simons Foundation

Keyword: Hearing
Link ID: 29115 - Posted: 01.27.2024

Allison Aubrey Among the roughly 40 million adults in the U.S. who have hearing loss, most don't use hearing aids. This means they may be missing out on more than just good hearing. Research shows hearing loss, if left untreated, can increase the risk of frailty, falls, social isolation, depression and cognitive decline. One study from scientists at Johns Hopkins University found that even people with mild hearing loss doubled their risk of dementia. Now a new study finds that restoring hearing loss with hearing aids may lengthen people's lives. Dr. Janet Choi, an otolaryngologist with Keck Medicine of USC, wanted to evaluate whether restoring hearing with hearing aids may increase the chances of living longer. Using data from the the National Health and Nutrition Examination Survey, a large, national study, Choi and her colleagues tracked the status of nearly 1,900 adults who had been shown to have hearing loss during screenings. The participants completed questionnaires about their use of hearing aids. "The group of patients who were using hearing aids regularly had a 24% lower risk of mortality compared to the group who never use hearing aids," Choi says. Meaning, the participants who were in the habit of wearing hearing aids were significantly less likely to die early. The researchers had hypothesized this would be the case given all the studies pointing to the negative impacts of untreated hearing loss. But Choi says they did not expect such a big difference in mortality risk. "We were surprised," she says. Prior research has shown that age-related hearing loss – if untreated – can take its toll on physical and mental health. And a recent study found restoring hearing with hearing aids may slow cognitive decline among people at high risk. © 2024 npr

Keyword: Hearing
Link ID: 29079 - Posted: 01.06.2024

Rudi Zygadlo To celebrate our anniversary, my partner and I dine in a trendy London restaurant in Hackney with a Michelin star – my first time in such a place. A crispy little bonbon is introduced to us simply as “Pine, kvass lees and vin brûlé.” I watch my partner light up, the flickering candle in her eyes, as the waiter sets the thing down. The impact of the aroma has already registered on her face. With her first bite she is transported to her childhood in Massachusetts. “Gosh,” she gasps, closing her eyes as a New England virgin pine forest explodes in her mind. When she blinks open, returning to the here and now, she looks at me guiltily. I take a bite and wince. No coniferous wonderland for me. Just unpleasant bitterness, confined very much to the tongue. I am pleased for her, truly. I’m a magnanimous guy. But from that moment on, the whole evening is a bit of a spectator sport and, by the end of it, I have a feeling that she is even playing her enjoyment down, muting her reactions, as if to say, “You’re not missing out.” She finds some dishes prove more successful than others – the sweetness of cherry, an umami-rich mushroom – but I am missing out: on the nuances, the emotions, the memories. The smell. It’s been three years since I lost it. November 2020. I was living with three friends in a flat in Glasgow when we all caught Covid in the pre-vaccine days. Two of us lost our smell and never fully recovered it. We’re in good company. Around 700,000 people in the UK are believed to have total smell loss caused by the virus, with around six million still experiencing some olfactory dysfunction. I estimate mine has returned by about 30%, but it’s inconsistent and often distorted. To summarise my symptoms of anosmia, as total or partial loss of smell is known: some things have a faint odour, some don’t smell as they should and others don’t smell at all. For example: basil smells mild but good, ground coffee and a certain brand of toothpaste smell like fish and, mercifully, shit doesn’t stink at all. Apart from the latter, all bad news.

Keyword: Chemical Senses (Smell & Taste)
Link ID: 29070 - Posted: 12.31.2023

By Esther Landhuis When Frank Lin was in junior high, his grandma started wearing hearing aids. During dinner conversations, she was often painfully silent, and communicating by phone was nearly impossible. As a kid, Lin imagined “what her life would be like if she wasn’t always struggling to communicate.” It was around that time that Lin became interested in otolaryngology, the study of the ears, nose, and throat. He would go on to study to be an ENT physician, which, he hoped, could equip him to help patients with similar age-related hardships. Those aspirations sharpened during his residency at Johns Hopkins University School of Medicine in the late 2000s. Administering hearing tests in the clinic, Lin noticed that his colleagues had vastly different reactions to the same results in young versus old patients. If mild deficits showed up in a kid, “it would be like, ‘Oh, that hearing is critically important,’” said Lin, who today is the director of the Cochlear Center for Hearing and Public Health at Hopkins. But when they saw that same mild to moderate hearing loss in a 70-something patient, many would downplay the findings. Yet today, research increasingly suggests that untreated hearing loss puts people at higher risk for cognitive decline and dementia. And, unlike during Lin’s early training, many patients can now do something about it: They can assess their own hearing using online tests or mobile phone apps, and purchase over-the-counter hearing aids, which are generally more affordable their predecessors and came under regulation by the Food and Drug Administration in October 2022. Despite this expanded accessibility, interest in direct-to-consumer hearing devices has lagged thus far — in part, experts suggest, due to physician inattention to adult hearing health, inadequate insurance coverage for hearing aids, and lingering stigma around the issue. (As Lin put it: “There’s always been this notion that everyone has it as you get older, how can it be important?”) Even now, hearing tests aren’t necessarily recommended for individuals unless they report a problem.

Keyword: Hearing; Alzheimers
Link ID: 29064 - Posted: 12.27.2023

Alex Johnson The holiday season is upon us, and with it, opportunities to indulge in festive treats. The proverbial saying “you eat with your eyes first” seems particularly relevant at this time of year. The science behind eating behavior, however, reveals that the process of deciding what, when and how much to eat is far more complex than just consuming calories when your body needs fuel. Hunger cues are only part of why people choose to eat. As a scientist interested in the psychology and biology that drives eating behavior, I’m fascinated with how the brain’s experiences with food shape eating decisions. Food-related visual cues can shape feeding behaviors in both people and animals. For example, wrapping food in McDonald’s packaging is sufficient to enhance taste preferences across a range of foods – from chicken nuggets to carrots – in young children. Visual food-related cues, such as presenting a light when food is delivered, can also promote overeating behaviors in animals by overriding energy needs. In fact, a whole host of sensory stimuli – noises, smells and textures – can be associated with the pleasurable consequences of eating and influence food-related decisions. This is why hearing a catchy radio jingle for a food brand, seeing a television ad for a restaurant or walking by your favorite eatery can shape your decision to consume and sometimes overindulge.

Keyword: Obesity; Chemical Senses (Smell & Taste)
Link ID: 29060 - Posted: 12.22.2023

By Carolyn Wilke Newborn bottlenose dolphins sport a row of hairs along the tops of their jaws. But once the animals are weaned, the whiskers fall out. “Everybody thought these structures are vestigial — so without any function,” said Guido Dehnhardt, a marine mammal zoologist at the University of Rostock in Germany. But Dr. Dehnhardt and his colleagues have discovered that the pits left by those hairs can perceive electricity with enough sensitivity that they may help the dolphins snag fish or navigate the ocean. The team reported its findings Thursday in The Journal of Experimental Biology. Dr. Dehnhardt first studied the whisker pits of a different species, the Guiana dolphin. He expected to find the typical structures of hair follicles, but those were missing. Yet the pits were loaded with nerve endings. He and his colleagues realized that the hairless follicles looked like the electricity-sensing structures on sharks and found that one Guiana dolphin responded to electrical signals. They wondered whether other toothed cetaceans, including bottlenose dolphins, could also sense electricity. For the new study, the researchers trained two bottlenose dolphins to rest their jaws, or rostrums, on a platform and swim away anytime they experienced a sensory cue like a sound or a flash of light. If they didn’t detect one of these signals, the dolphins were to stay put. “It’s basically the same as when we go to the doctor’s and do a hearing test — we have to press a button as soon as we hear a sound,” said Tim Hüttner, a biologist at the Nuremberg Zoo in Germany and a study co-author. Once trained, the dolphins also received electrical signals. “The dolphins responded correctly on the first trial,” Dr. Hüttner said. The animals were able to transfer what they had learned, revealing that they could also detect electric fields. Further study showed that the dolphins’ sensitivity to electricity was similar to that of the platypus, which is thought to use its electrical sense for foraging. © 2023 The New York Times Company

Keyword: Hearing
Link ID: 29037 - Posted: 12.09.2023

Jon Hamilton If this year's turkey seems over brined, blame your brain. The question of when salty becomes too salty is decided by a special set of neurons in the front of the brain, researchers report in the journal Cell. A separate set of neurons in the back of the brain adjusts your appetite for salt, the researchers showed in a series of experiments on mice. "Sodium craving and sodium tolerance are controlled by completely different types of neurons," says Yuki Oka, an author of the study and a professor of biology at Caltech. The finding could have health implications because salt ingestion is a "major issue" in many countries, including the United States, says Nirupa Chaudhari, a professor of physiology and biology at the University of Miami's Miller School of Medicine. Too much salt can cause high blood pressure and raise the risk for heart disease and stroke, says Chaudhari, who was not involved in the study. Craving, to a point The study sought to explain the complicated relationship that people and animals have with salt, also known as sodium chloride. We are happy to drink sodas, sports drinks, and even tap water that contain a little salt, Oka says. "But if you imagine a very high concentration of sodium like ocean water, you really hate it." This aversion to super salty foods and beverages holds unless your body is really low on salt, something that's pretty rare in people these days. But experiments with mice found that when salt levels plummet, the tolerance for salty water goes up. "Animals start liking ocean water," Oka says. The reason for this change involves at least two different interactions between the body and brain, Oka's team found. When the concentration of sodium in the bloodstream begins to fall below healthy levels, a set of neurons in the back of the brain respond by dialing up an animal's craving for salt. "If you stimulate these neurons, then animals run to a sodium source and start eating," Oka says. Meanwhile, a different set of neurons in the front of the brain monitors the saltiness of any food or water the mice are consuming. And usually, these neurons will set an upper limit on saltiness. © 2023 npr

Keyword: Chemical Senses (Smell & Taste); Obesity
Link ID: 29024 - Posted: 11.26.2023

By Sandra G. Boodman The first sign of trouble was difficulty reading. In late 2014 Cathy A. Haft, a New York real estate broker who divides her time between Brooklyn and Long Island, thought she needed new glasses. But an eye exam found that her prescription was largely unchanged. Bladder problems came next, followed by impaired balance, intermittent dizziness and unexplained falls. By 2018 Haft, unable to show properties because she was too unsteady on her feet, was forced to retire. For the next four years specialists evaluated her for neuromuscular and balance-related ear problems in an attempt to explain her worsening condition, which came to include cognitive changes her husband feared was Alzheimer’s disease. In August 2022 Haft, by then dependent on a walker, consulted a Manhattan neurosurgeon. After observing her gait and reviewing images from a recent brain scan, he sent her to a colleague. Less than eight weeks later Haft underwent brain surgery for a condition that is frequently unrecognized or misdiagnosed. The operation succeeded in restoring skills that had gradually slipped away, stunting Haft’s life. “It’s pretty astonishing that this disorder is not that uncommon and no one put the pieces together,” she said. In her case a confluence of confounding symptoms, a complex medical history and the possible failure to take a holistic approach may have led doctors to overlook a condition that can sometimes be reversed — with dramatic results.

Keyword: Movement Disorders; Alzheimers
Link ID: 29020 - Posted: 11.26.2023

By Hannah Docter-Loeb Paxlovid can prevent severe illness from COVID-19, but it comes with a price: In many users, the antiviral drug leaves a weird, metallic aftertaste that can last for days—a condition nicknamed “Paxlovid mouth.” Now, researchers say they’ve figured out why. A component of Paxlovid activates one of the tongue’s bitter taste receptors even at low levels, which may draw out the yuck factor, the team reports this month in Biochemical and Biophysical Research Communications. The work could lead to ways to alleviate the unpleasant side effect. The study is a “good first step” in teasing apart the mechanism behind Paxlovid mouth, says Alissa Nolden, a sensory scientist at the University of Massachusetts Amherst who was not involved with the research. But she says more work will be needed to truly understand why the metallic taste lingers for so long. Paxlovid is composed of two antivirals: nirmatrelvir and ritonavir. Nirmatrelvir blocks a key protein that SARS-CoV-2 needs to replicate. Ritonavir helps maintain the level of nirmatrelvir in the blood. Scientists have suspected that ritonavir is the primary culprit behind Paxlovid mouth. It was originally used in HIV medications and was known to directly taste bitter. A recent study also demonstrated that the compound acts on several tongue receptors that respond to bitter taste. However, ritonavir’s bitterness is short-lived, says Peihua Jiang, a molecular biologist at the Monell Chemical Senses Center, an independent research institute. So in the new study, he and colleagues looked more closely at nirmatrelvir. They added the antiviral to various groups of cells, each collection with a different member of the 25 human bitter taste receptors. They then identified the receptors that responded most vigorously to the compound by changes in a fluorescence marker in the cells. Nirmatrelvir seemed to hone in on TAS2R1, one of the primary receptors responsible for the bitter aftertaste of antiviral medicines, the researchers found. The compound activated the receptor even when its concentration was relatively low, which could explain why Paxlovid causes a persistent bitter taste.

Keyword: Chemical Senses (Smell & Taste)
Link ID: 29016 - Posted: 11.22.2023

By Timmy Broderick Smell is probably our most underappreciated sense. “If you ask people which sense they would be most willing to give up, it would be the olfactory system,” says Michael Leon, a neurobiologist at the University of California, Irvine. But a loss of smell has been linked to health complications such as depression and cognitive decline. And mounting evidence shows that olfactory training, which involves deliberately smelling strong scents on a regular basis, may help stave off that decline. Now a team of researchers led by Leon has successfully boosted cognitive performance by exposing people to smells while they sleep. Twenty participants—all older than 60 years and generally healthy—received six months of overnight olfactory enrichment, and all significantly improved their ability to recall lists of words compared with a control group. The study appeared in Frontiers in Neuroscience. The scientists are unsure about how the overnight odors may have produced this result, but Leon notes that the neurons involved in olfaction have “direct superhighway access” to brain regions related to memory and emotion. In participants who received the treatment, the study authors observed physical changes in a brain structure that connects the memory and emotional centers—a pathway that often deteriorates as people age, especially in those with Alzheimer's disease. Previous successful attempts to boost memory with odors typically relied on complicated interventions with multiple exposures a day. If the nighttime treatment proves successful in larger trials, it promises to be a less intrusive way to achieve similar effects, says Vidya Kamath, a neuropsychologist at the Johns Hopkins University School of Medicine, who was not involved in the recent study. Larger trials may also help answer some remaining questions. The new study used widely available essential oils such as rose and eucalyptus, but researchers aren't sure if just any odor would get the same results. They don't know how much an odor's qualities—whether it's foul or pleasant to people, for example—affects the cognitive gains. It is also unclear how much novelty plays a role, says Michał Pieniak, a psychology researcher at the University of Wroclaw in Poland who has studied olfactory training. © 2023 SCIENTIFIC AMERICAN,

Keyword: Sleep; Learning & Memory
Link ID: 29010 - Posted: 11.18.2023

By Sean Cummings If a bite of dandelion greens or extra-dark chocolate makes you pucker, there’s good reason. Bitterness can indicate the presence of toxins in potential foods, and animals long ago honed the ability to ferret out harsh tastes. But the ability to sense bitterness may be even older than many presumed, a new study finds. It likely first evolved in vertebrates roughly 460 million years ago, when sharks and other cartilaginous fishes separated from bony vertebrates like ourselves, researchers report today in the Proceedings of the National Academy of Sciences. The bitter taste receptor identified in a pair of shark species may mirror a sort of all-purpose bitterness detector that our common ancestor possessed. “Given how quickly taste receptors change, to have this one receptor conserved over 460 million years, that’s pretty astounding,” says Craig Montell, a neurobiologist at the University of California, Santa Barbara who was not involved in the study. “The ability to react to the particular bitter chemicals that activate it must be really important.” Humans and other bony vertebrates experience bitterness thanks to taste 2 receptors, or T2Rs, which are proteins that transmit taste information to the brain. But scientists had never found T2Rs in cartilaginous vertebrates such as sharks and rays. That led many to assume these receptors had evolved after their lineage split from the bony vertebrates. Yet sharks and other cartilaginous fish do have smell receptors closely related to bitter taste receptors. That made Sigrun Korsching, a neurobiologist at the University of Cologne, wonder: Could bitter taste perception be even older than most believed? To find out, she and colleagues examined 17 genomes from various species of sharks, skates, and sawfish. Twelve of these had genes that coded for taste receptors similar to T2Rs, which they dubbed T2R1s. In the lab, the researchers implanted genes for these receptors from two of the species—bamboo sharks and catsharks—into human kidney cells, then exposed them to 94 bitter substances. These included resveratrol, found in foods such as grapes, peanuts, and cranberries, and amarogentin, a compound from the gentian plant considered one of the most astringent tastes in the world.

Keyword: Chemical Senses (Smell & Taste); Evolution
Link ID: 29006 - Posted: 11.15.2023

Saima Sidik When the scent of morning coffee wafts past the nose, the brain encodes which nostril it enters, new research shows1. Integrating information from both nostrils might help us to identify the odour. The results were published today in Current Biology. A region of the brain called the piriform cortex, which spans the brain’s two hemispheres, is known to receive and process information about scents. However, scientists were unsure whether the two sides of the piriform cortex react to smells in unison or independently. To investigate this question, researchers recruited people with epilepsy who were undergoing brain surgery to identify the areas of their brains responsible for their seizures. Participants were awake for the surgery, during which the scientists delivered scents to one or both nostrils through tiny tubes that reached roughly one centimetre into each nostril. The authors took advantage of electrodes placed in the study participants’ brains to take readings of activity in the piriform cortex. In reality, scents rarely hit only one nostril. Instead, they’re likely to enter one nostril slightly ahead of the other. “The question to ask is, well, can the brain exploit these potential differences?” says Naz Dikecligil, a neuroscientist at the University of Pennsylvania in Philadelphia and a co-author of the study. The findings suggest that the brain does make use of the different arrival times. When an odour was delivered to a single nostril, the side of the brain closest to that nostril reacted first, and a reaction then followed in the opposite side of the brain. “There seem to be actually two odour representations, corresponding to odour information coming from each nostril,” Dikecligil says. When the researchers provided a scent to both nostrils simultaneously, they saw that both sides of the brain recognized the scent faster than either did when it was delivered through only one nostril. This suggests that the two sides do synergize to some degree, even though one lags behind the other in encoding a scent, Dikecligil says. © 2023 Springer Nature Limited

Keyword: Chemical Senses (Smell & Taste)
Link ID: 28992 - Posted: 11.08.2023

By Paula Span A year ago, the Food and Drug Administration announced new regulations allowing the sale of over-the-counter hearing aids and setting standards for their safety and effectiveness. That step — which was supposed to take three years but required five — portended cheaper, high-quality hearing aids that people with mild to moderate hearing loss could buy online or at local pharmacies and big stores. So how’s it going? It’s a mixed picture. Manufacturers and retailers have become serious about making hearing aids more accessible and affordable. Yet the O.T.C. market remains confusing, if not downright chaotic, for the mostly older consumers the new regulations were intended to help. The past year also brought renewed focus on the importance of treating hearing loss, which affects two-thirds of people over age 70. Researchers at Johns Hopkins University published the first randomized clinical trial showing that hearing aids could help reduce the pace of cognitive decline. Some background: In 2020, the influential Lancet Commission on Dementia Prevention, Intervention and Care identified hearing loss as the greatest potentially modifiable risk factor for dementia. Previous studies had demonstrated a link between hearing loss and cognitive decline, said Dr. Frank Lin, an otolaryngologist and epidemiologist at Johns Hopkins and lead author of the new research. “What remained unanswered was, If we treat hearing loss, does it actually reduce cognitive loss?” he said. The ACHIEVE study (for Aging and Cognitive Health Evaluation in Elders) showed that, at least for a particular group of older adults, it could. Of nearly 1,000 people ages 70 to 84 with untreated mild to moderate hearing loss, half received hearing assessments from audiologists, were fitted with midpriced hearing aids and were counseled on how to use them for several months. The control group participated in a health education program. Over three years, the study found that hearing-aid use had scant effect on healthy volunteers at low risk of cognitive loss. But among participants who were older and less affluent, hearing aids reduced the rate of cognitive decline by 48 percent, compared with the control group, a difference the researchers deemed “clinically meaningful.” © 2023 The New York Times Company

Keyword: Hearing; Alzheimers
Link ID: 28979 - Posted: 11.01.2023

Max Kozlov Rich, high-fat foods such as ice cream are loved not only for their taste, but also for the physical sensations they produce in the mouth — their ‘mouthfeel’. Now scientists have identified a brain area that both responds to the smooth texture of fatty foods and uses that information to rate the morsel’s allure, guiding eating behaviour1. These findings, published on 16 October in The Journal of Neuroscience, “add a new dimension” of the eating experience to scientists’ understanding of what motivates people to choose certain foods, says Ivan de Araujo, a neuroscientist at the Max Planck Institute for Biological Cybernetics in Tübingen, Germany, who was not involved in the study. To explore how food textures influence eating habits, Fabian Grabenhorst, a neuroscientist at the University of Oxford, UK, and his colleagues set out to quantify the mouthfeel of fatty foods. The authors prepared several milkshakes with varying fat and sugar contents and placed a sample of each between two pig tongues procured from a local butcher. The researchers then slid the tongues across each other and measured the amount of friction between the two surfaces, providing a numerical index of each shake’s smoothness. The researchers then gave 22 participants milkshakes with the same compositions as those tested on the pig tongues. After tasting each milkshake, participants placed bids on how much they would spend to drink a full glass of it after the experiment. Accompanying brain scans showed that activity patterns in an area called the orbitofrontal cortex (OFC), which is involved in reward processing, reflected the shakes’ texture. The scans also identified OFC activity patterns that reflected participants’ bids, suggesting that this brain region links mouthfeel to the value placed on that food. © 2023 Springer Nature Limited

Keyword: Obesity; Chemical Senses (Smell & Taste)
Link ID: 28966 - Posted: 10.17.2023

By Tim Vernimmen For humans, division of labor has become a necessity: No person in the world has all the knowledge and skills to perform all the tasks that are required to keep our highly technological societies afloat. This has made us entirely dependent on each other, leaving us individually vulnerable. We really can’t make it on our own. From archaeological findings, we can reconstruct more or less how this situation evolved. Initially, everyone was doing more or less the same thing. But because food was shared among people living in hunter-gatherer groups, some were able to specialize in tasks other than finding food, such as fashioning tools, treating illnesses or cultivating plants. These skills enriched the group but made the specialists even more dependent on others. This further reinforced cooperation among group members and pushed our species to even higher levels of specialization — and prosperity. “Societies that have highly developed task-sharing and division of labor between group members are conspicuous because of their exceptional ecological success,” says Michael Taborsky, a behavioral biologist at the University of Bern in Switzerland. And he doesn’t just mean us: Extensive division of labor also can be seen among many social insects — ants, wasps, bees and termites — in which individuals in large colonies often specialize in particular tasks, making them impressively effective. “It is no exaggeration,” Taborsky says, “to say that societies” — of both humans and social insects — “predominate life on Earth.” But how did this division of labor evolve? Why does it seem to be rare outside of our species and the social insects? Is it, in fact, as rare as it seems? Taborsky, who has studied cooperation in animals for decades, has become increasingly interested in these questions. In March 2023, he and Barbara Taborsky, his wife and colleague, organized a scientific workshop on the topic in Berlin to which they invited a number of other experts. Over the course of two days, the group discussed how division of labor may have evolved over time, and what mechanisms allow it to develop, over and over again, in every colony of certain species. One of the invited scientists was Jennifer Fewell, a social insect biologist at Arizona State University who coauthored an influential overview of division of labor in the Annual Review of Entomology in 2001 and has studied the subject for decades. In social insect colonies, she says, “there is no central controller telling everybody what to do, but instead, the division of labor emerges from the interaction between individuals.” © 2023 Annual Reviews

Keyword: Chemical Senses (Smell & Taste); Evolution
Link ID: 28944 - Posted: 10.05.2023

By Hannah Docter-Loeb Growing up, Julian Meeks knew what a life without a sense of smell could look like. He’d watched this grandfather navigate the condition, known as anosmia, observing that he didn’t perceive flavor and only enjoyed eating very salty or meaty foods. The experience influenced him, in part, to study chemosensation, which involves both smell and taste. Meeks, now a professor of neuroscience at the University of Rochester, told Undark that neither gets much attention compared to other senses: “Often, they’re thought of as second or third in order of importance.” The pandemic changed that, at least somewhat, after it left millions of people without a sense of smell, albeit some temporarily. In particular, more researchers started looking at a specific type of condition called acquired anosmia. Common causes include traumatic brain injury, or TBI, neurodegenerative diseases like Parkinson’s or Alzheimer’s, or following a viral infection like Covid-19. Due to the pandemic, “many people found it scientifically interesting to focus their research on smell,” said Valentina Parma, the assistant director of the Monell Chemical Senses Center, a nonprofit research institute in Philadelphia. By one account, NIH funding of anosmia research nearly doubled between 2019 and 2021. But many of the research findings do not apply to those who have lacked the ability to smell since birth: congenital anosmics. And, despite the increased attention to smell loss more broadly, some researchers still face challenges in funding studies. In March 2023, for instance, Meeks received a peer review for a small grant, of less than $275,000, from the National Institutes of Health, with which he had planned to look into anosmia in the context of TBI. For Meeks, the response was frustrating. One expert reviewer in particular “didn’t really understand why there would be any need to establish a preclinical model of anosmia with TBI,” he said, noting that the reviewer also wrote that because anosmia is not a major health problem, the value of the research was low. The comment, Meeks added, was “quite discouraging.”

Keyword: Chemical Senses (Smell & Taste)
Link ID: 28931 - Posted: 09.27.2023

By Amber Dance We’ve all heard of the five tastes our tongues can detect — sweet, sour, bitter, savory-umami and salty. But the real number is actually six, because we have two separate salt-taste systems. One of them detects the attractive, relatively low levels of salt that make potato chips taste delicious. The other one registers high levels of salt — enough to make overly salted food offensive and deter overconsumption. Exactly how our taste buds sense the two kinds of saltiness is a mystery that’s taken some 40 years of scientific inquiry to unravel, and researchers haven’t solved all the details yet. In fact, the more they look at salt sensation, the weirder it gets. Many other details of taste have been worked out over the past 25 years. For sweet, bitter and umami, it’s known that molecular receptors on certain taste bud cells recognize the food molecules and, when activated, kick off a series of events that ultimately sends signals to the brain. Sour is slightly different: It is detected by taste bud cells that respond to acidity, researchers recently learned. In the case of salt, scientists understand many details about the low-salt receptor, but a complete description of the high-salt receptor has lagged, as has an understanding of which taste bud cells host each detector. “There are a lot of gaps still in our knowledge — especially salt taste. I would call it one of the biggest gaps,” says Maik Behrens, a taste researcher at the Leibniz Institute for Food Systems Biology in Freising, Germany. “There are always missing pieces in the puzzle.” A fine balance Our dual perception of saltiness helps us to walk a tightrope between the two faces of sodium, an element that’s crucial for the function of muscles and nerves but dangerous in high quantities. To tightly control salt levels, the body manages the amount of sodium it lets out in urine, and controls how much comes in through the mouth. © 2023 Annual Reviews

Keyword: Chemical Senses (Smell & Taste)
Link ID: 28908 - Posted: 09.16.2023

By David Grimm Apart from Garfield’s legendary love of lasagna, perhaps no food is more associated with cats than tuna. The dish is a staple of everything from The New Yorker cartoons to Meow Mix jingles—and more than 6% of all wild-caught fish goes into cat food. Yet tuna (or any seafood for that matter) is an odd favorite for an animal that evolved in the desert. Now, researchers say they have found a biological explanation for this curious craving. In a study published this month in Chemical Senses, scientists report that cat taste buds contain the receptors needed to detect umami—the savory, deep flavor of various meats, and one of the five basic tastes in addition to sweet, sour, salty, and bitter. Indeed, umami appears to be the primary flavor cats seek out. That’s no surprise for an obligate carnivore. But the team also found these cat receptors are uniquely tuned to molecules found at high concentrations in tuna, revealing why our feline friends seem to prefer this delicacy over all others. “This is an important study that will help us better understand the preferences of our familiar pets,” says Yasuka Toda, a molecular biologist at Meiji University and a leader in studying the evolution of umami taste in mammals and birds. The work could help pet food companies develop healthier diets and more palatable medications for cats, says Toda, who was not involved with the industry-funded study. Cats have a unique palate. They can’t taste sugar because they lack a key protein for sensing it. That’s probably because there’s no sugar in meat, says Scott McGrane, a flavor scientist and research manager for the sensory science team at the Waltham Petcare Science Institute, which is owned by pet food–maker Mars Petcare UK. There’s a saying in evolution, he says: “If you don’t use it, you lose it.” Cats also have fewer bitter taste receptors than humans do—a common trait in uber-carnivores. But cats must taste something, McGrane reasoned, and that something is likely the savory flavor of meat. In humans and many other animals, two genes—Tas1r1 and Tas1r3—encode proteins that join together in taste buds to form a receptor that detects umami. Previous work had shown that cats express the Tas1r3 gene in their taste buds, but it was unclear whether they had the other critical puzzle piece.

Keyword: Chemical Senses (Smell & Taste); Evolution
Link ID: 28885 - Posted: 08.26.2023