Chapter 6. Hearing, Balance, Taste, and Smell
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By BENEDICT CAREY A Polish man who was paralyzed from the chest down after a knife attack several years ago is now able to get around using a walker and has recovered some sensation in his legs after receiving a novel nerve-regeneration treatment, according to a new report that has generated both hope and controversy. The case, first reported widely by the BBC and other British news outlets, has stirred as much excitement on the Internet as it has extreme caution among many experts. “It is premature at best, and at worst inappropriate, to draw any conclusions from a single patient,” said Dr. Mark H. Tuszynski, director of the translational neuroscience unit at the medical school of the University of California, San Diego. That patient — identified as Darek Fidyka, 40 — is the first to recover feeling and mobility after getting the novel therapy, which involves injections of cultured cells at the site of the injury and tissue grafts, the report said. The techniques have shown some promise in animal studies. But the medical team, led by Polish and English doctors, also emphasized that the results would “have to be confirmed in a larger group of patients sustaining similar types of spinal injury” before the treatment could be considered truly effective. The case report was published in the journal Cell Transplantation. The history of spinal injury treatment is studded with false hope and miracle recoveries that could never be replicated, experts said. In previous studies, scientists experimented with some of the same methods used on Mr. Fidyka, with disappointing results. © 2014 The New York Times Company
|By Steve Mirsky People have been leaving messages on bathroom walls for thousands of years. Just google “ancient Roman bathroom graffiti.” But we’re not the only ones to use latrines for information exchange—as two German researchers have confirmed after hundreds of hours watching lemurs pee and poop. For science. Primatologists Iris Dröscher and Peter Kappeler concentrated on seven sets of pair-bonded members of a species called white-footed sportive lemurs, at a nature reserve in southern Madagascar. Their report is in the journal Behavioral Ecology and Sociobiology. [Iris Dröscher & Peter M. Kappeler Maintenance of familiarity and social bonding via communal latrine use in a solitary primate (Lepilemur leucopus)] Many animals use the same spots repeatedly to do their business, primates in particular. For these lemurs, a specific tree becomes the urine and feces focal point. And because chemical compounds in their waste transmit information, the so-called latrine tree becomes like a bulletin board to post messages for the rest of the community. Based on their 1,097 hours of observations, the researchers conclude that urine and glandular secretions left on the tree trunk are the primary message vehicles. Feces mostly just collects on the ground. Some urine telegrams are probably signals from a particular lemur to the neighbors that he or she is around. But male lemurs upped their latrine visits when potential competitors for females came into their home area. So the frequent chemical messages left on the tree probably say in that case, “Buzz off, buddy, she’s with me.” In lemur. © 2014 Scientific American,
By ALEX STONE Smell is one of the oldest human faculties, yet it was one of the last to be understood by scientists. It was not until the early 1990s that biologists first described the inner workings of olfactory receptors — the chemical sensors in our noses — in a discovery that won a Nobel Prize. Since then, the plot has thickened. Over the last decade or so, scientists have discovered that odor receptors are not solely confined to the nose, but found throughout body — in the liver, the heart, the kidneys and even sperm — where they play a pivotal role in a host of physiological functions. Now, a team of biologists at Ruhr University Bochum in Germany has found that our skin is bristling with olfactory receptors. “More than 15 of the olfactory receptors that exist in the nose are also found in human skin cells,” said the lead researcher, Dr. Hanns Hatt. Not only that, but exposing one of these receptors (colorfully named OR2AT4) to a synthetic sandalwood odor known as Sandalore sets off a cascade of molecular signals that appears to induce healing in injured tissue. In a series of human tests, skin abrasions healed 30 percent faster in the presence of Sandalore, a finding the scientists think could lead to cosmetic products for aging skin and to new treatments to promote recovery after physical trauma. The presence of scent receptors outside the nose may seem odd at first, but as Dr. Hatt and others have observed, odor receptors are among the most evolutionarily ancient chemical sensors in the body, capable of detecting a multitude of compounds, not solely those drifting through the air. “If you think of olfactory receptors as specialized chemical detectors, instead of as receptors in your nose that detect smell, then it makes a lot of sense for them to be in other places,” said Jennifer Pluznick, an assistant professor of physiology at Johns Hopkins University who in 2009 found that olfactory receptors help control metabolic function and regulate blood pressure in the kidneys of mice. © 2014 The New York Times Company
Keyword: Chemical Senses (Smell & Taste)
Link ID: 20206 - Posted: 10.14.2014
By Meredith Levine, Word went round Janice Mackay's quiet neighbourhood that she was hitting the bottle hard. She'd been seen more than once weaving along the sidewalk in front of her suburban home in Pickering, just outside Toronto, in a sad, drunken stagger. But Mackay wasn't drunk. As it turned out, her inner ear, the body's balance centre, had been destroyed by medication when she was hospitalized for over a month back in May 2005. At the time, Mackay was diagnosed with a life-threatening infection in one of her ovaries, and so was put on a cocktail of medication, including an IV drip of gentamicin, a well-known, inexpensive antibiotic that is one of the few that hasn't fallen prey to antibiotic-resistant bacteria. A few weeks later, the infection was almost gone when Mackay, still hospitalized, suddenly developed the bed spins and vomiting. Her medical team told her she'd been laying down too long and gave her Gravol, but the symptoms didn't go away. In a follow-up appointment after her discharge, Mackay was told that the dizziness was a side effect of the gentamicin, and that she would probably have to get used to it. But she didn't discover the extent of the damage until later when neurotologist Dr. John Rutka assessed her condition and concluded that the gentamicin had essentially destroyed her vestibular system, the body's motion detector, located deep within the inner ear. © CBC 2014
Link ID: 20198 - Posted: 10.13.2014
By David Shultz The next time you see a fruit fly hovering around your pint of beer, don’t swat it—appreciate it. You’re witnessing a unique relationship between yeast and insect. A new study reveals that the single-celled organisms have evolved to secrete a fruity scent that attracts fruit flies, which they hitch a ride on for greener pastures. The findings may also explain the sweet aroma of some craft beers. Like many scientific discoveries, the new work was the product of a happy accident. Kevin Verstrepen, a geneticist at KU Leuven in Belgium, was working with two types of yeast: a normal strain and another with a mutation in a gene called ATF1 that causes the cells to produce fewer odors during fermentation. “Nobody really knew what was happening until I was lazy enough to leave the lab on a Friday with these yeast left out on the bench,” he says. By coincidence, a group of fruit flies (Drosophila melanogaster) chose that weekend to escape from a neighboring genetics lab. When Verstrepen returned to work on Monday, he discovered that the insects had found their way into the smelly yeast culture but had ignored the mutant colony. To probe further, Verstrepen and colleagues set up an enclosed “arena” and pumped ATF1 aromas, which are either fruity, flowery, or solventlike, into one corner. Another corner received a dose of odors from the ATF1-deficient yeast. The remaining two corners emitted odorless streams of air to serve as controls. As expected, the flies congregated almost exclusively in the corner emitting the fragrant odors of yeast with intact ATF1 genes. Analyses of the insects’ brains revealed that the neurons in flies exposed to smelly yeast responded in an entirely different way from those exposed to odorless air or the scent of ATF1-deficient yeast strain, the researchers report online today in Cell Reports. © 2014 American Association for the Advancement of Science
Keyword: Chemical Senses (Smell & Taste)
Link ID: 20192 - Posted: 10.11.2014
For decades, scientists thought that neurons in the brain were born only during the early development period and could not be replenished. More recently, however, they discovered cells with the ability to divide and turn into new neurons in specific brain regions. The function of these neuroprogenitor cells remains an intense area of research. Scientists at the National Institutes of Health (NIH) report that newly formed brain cells in the mouse olfactory system — the area that processes smells — play a critical role in maintaining proper connections. The results were published in the October 8 issue of the Journal of Neuroscience. “This is a surprising new role for brain stem cells and changes the way we view them,” said Leonardo Belluscio, Ph.D., a scientist at NIH’s National Institute of Neurological Disorders and Stroke (NINDS) and lead author of the study. The olfactory bulb is located in the front of the brain and receives information directly from the nose about odors in the environment. Neurons in the olfactory bulb sort that information and relay the signals to the rest of the brain, at which point we become aware of the smells we are experiencing. Olfactory loss is often an early symptom in a variety of neurological disorders, including Alzheimer’s and Parkinson’s diseases. In a process known as neurogenesis, adult-born neuroprogenitor cells are generated in the subventricular zone deep in the brain and migrate to the olfactory bulb where they assume their final positions. Once in place, they form connections with existing cells and are incorporated into the circuitry.
By Sarah C. P. Williams When a group of male katydids croon a tune in nearly perfect synchrony, it means the insects are after the ladies. But they’re not aligning their singing with each other to come across as larger or louder, a new study finds; each male is trying to beat out the others to be the first—by mere milliseconds—to hit a note. Katydids, also known as bush crickets (Mecopoda elongata), are among a handful of insects that make noise by rubbing a hind leg on one wing. Scientists knew that the sound attracted females, but they didn’t know why the males sang in synchrony. In the new study, researchers recorded and analyzed the choral performances of 18 different groups of four male katydids. Then, they let females choose between the males in each group. Females preferred males that were the first to broadcast each tone, even if it were only 70 milliseconds ahead of others in the group, the team reports online today in Royal Society Open Science. Moreover, the females preferred these lead singers to katydids that were singing alone—but the increased volume of the chorus didn’t seem to draw more females to the group as a whole. Singing in a group, the authors of the new study hypothesize, might help keep males on a steady rhythm—another trait that female katydids in the study preferred. But more work is needed to figure out why females chose the steadiest, leading singer, and whether the observation holds true in all species of katydids, like the round-headed katydid (pictured) that's more common in North America. © 2014 American Association for the Advancement of Science
BY Bethany Brookshire In this sweet, sweet world we live in, losing weight can be a dull and flavorless experience. Lovely stove-popped popcorn drenched in butter gives way to dry microwaved half-burnt kernels covered in dusty yellow powder. The cookies and candy that help us get through the long afternoons are replaced with virtuous but boring apples and nuts. Even the sugar that livens up our coffee gets a skeptical eye: That’s an extra 23 calories per packet you shouldn’t be eating. What makes life sweet for those of us who are counting calories is artificial sweeteners. Diet soda gives a sweet carbonated fix. A packet of artificial sweetener in your coffee or tea makes it a delicious morning dose. But a new study, published September 17 in Nature, found that the artificial sweetener saccharin has an unintended side effect: It alters the bacterial composition of the gut in mice and humans. The new bacterial neighborhood brings with it higher blood glucose levels, putting the humans and the murine counterparts at risk for diabetes. Many people wondered if the study’s effects were real. We all knew that sugar was bad, but now the scientists are coming for our Splenda! It seems more than a little unfair. But this study was a long time coming. The scientific community has been studying artificial sweeteners and their potential hazards for a long time. And while the new study adds to the literature, there are other studies, currently ongoing and planned for the future, that will determine the extent and necessity of our artificially sweetened future. © Society for Science & the Public 2000 - 2014.
By Smitha Mundasad Health reporter, BBC News Measuring people's sense of smell in later life could help doctors predict how likely they are to be alive in five years' time, a PLOS One study suggests. A survey of 3,000 adults found 39% with the poorest sense of smell were dead within five years - compared to just 10% who identified odours correctly. Scientists say the loss of smell sense does not cause death directly, but may be an early warning sign. They say anyone with long-lasting changes should seek medical advice. Researchers from the University of Chicago asked a representative sample of adults between the ages of 57-85 to take part in a quick smell test. The assessment involved identifying distinct odours encased on the tips of felt-tip pens. The smells included peppermint, fish, orange, rose and leather. Five years later some 39% of adults who had the lowest scores (4-5 errors) had passed away, compared with 19% with moderate smell loss and just 10% with a healthy sense of smell (0-1 errors). And despite taking issues such as age, nutrition, smoking habits, poverty and overall health into account, researchers found those with the poorest sense of smell were still at greatest risk. Lead scientist, Prof Jayant Pinto, said: "We think loss of the sense of smell is like the canary in the coal mine. BBC © 2014
By Sarah C. P. Williams A wind turbine, a roaring crowd at a football game, a jet engine running full throttle: Each of these things produces sound waves that are well below the frequencies humans can hear. But just because you can’t hear the low-frequency components of these sounds doesn’t mean they have no effect on your ears. Listening to just 90 seconds of low-frequency sound can change the way your inner ear works for minutes after the noise ends, a new study shows. “Low-frequency sound exposure has long been thought to be innocuous, and this study suggests that it’s not,” says audiology researcher Jeffery Lichtenhan of the Washington University School of Medicine in in St. Louis, who was not involved in the new work. Humans can generally sense sounds at frequencies between 20 and 20,000 cycles per second, or hertz (Hz)—although this range shrinks as a person ages. Prolonged exposure to loud noises within the audible range have long been known to cause hearing loss over time. But establishing the effect of sounds with frequencies under about 250 Hz has been harder. Even though they’re above the lower limit of 20 Hz, these low-frequency sounds tend to be either inaudible or barely audible, and people don’t always know when they’re exposed to them. For the new study, neurobiologist Markus Drexl and colleagues at the Ludwig Maximilian University in Munich, Germany, asked 21 volunteers with normal hearing to sit inside soundproof booths and then played a 30-Hz sound for 90 seconds. The deep, vibrating noise, Drexl says, is about what you might hear “if you open your car windows while you’re driving fast down a highway.” Then, they used probes to record the natural activity of the ear after the noise ended, taking advantage of a phenomenon dubbed spontaneous otoacoustic emissions (SOAEs) in which the healthy human ear itself emits faint whistling sounds. © 2014 American Association for the Advancement of Science
Link ID: 20144 - Posted: 10.01.2014
By Jia You Fish larvae emit sound—much to the surprise of biologists. A common coral reef fish in Florida, the gray snapper—Lutjanus griseus (pictured above)—hatches in the open ocean and spends its juvenile years in food-rich seagrass beds hiding from predators before settling in the reefs as an adult. To study how larval snappers orient themselves in the dark, marine biologists deployed transparent acrylic chambers equipped with light and sound sensors under the water to capture the swimming schools as they travel to the seagrass beds on new-moon nights. The larval snappers make a short “knock” sound that adults also make, as well as a long “growl” sound, the team reports online today in Biology Letters. The researchers suspect that the larvae use the acoustic signals to communicate with one another and stay together in schools. If so, human noise pollution could be interrupting their communications—even adult fish have been found to “yell” to be heard above boat noises. © 2014 American Association for the Advancement of Science.
By Sarah C. P. Williams Press the backs of your hands against the inside of a door frame for 30 seconds—as if you’re trying to widen the frame—and then let your arms down; you’ll feel something odd. Your arms will float up from your sides, as if lifted by an external force. Scientists call this Kohnstamm phenomenon, but you may know it as the floating arm trick. Now, researchers have studied what happens in a person’s brain and nerve cells when they repress this involuntary movement, holding their arms tightly by their sides instead of letting them float up. Two theories existed as to how this repression worked: The brain could send a positive “push down” signal to the arm muscles at the same time as the involuntary “lift up” signal was being transmitted to cancel it out; or the brain could entirely block the involuntary signal at the root of the nerves. The new study, which analyzed brain scans and muscle activity recordings from 39 volunteers, found that the latter was true—when a person stifles Kohnstamm phenomenon, the involuntary “lift” signal is blocked before it reaches the muscle. The difference between the repression mechanisms may seem subtle, but understanding it could help people repress other involuntary movements—including the tremors associated with Parkinson’s disease and the tics associated with Tourette syndrome, the team reports online today in the Proceedings of the Royal Society B. © 2014 American Association for the Advancement of Science
by Bob Holmes THERE'S something primal in a mother's response to a crying infant. So primal, in fact, that mother deer will rush protectively to the distress calls of other infant mammals, such as fur seals, marmots and even humans. This suggests such calls might share common elements – and perhaps that these animals experience similar emotions. Researchers – and, indeed, all pet owners – know that humans respond emotionally to the distress cries of their domestic animals, and there is some evidence that dogs also respond to human cries. However, most people have assumed this is a by-product of domestication. However, Susan Lingle, a biologist at the University of Winnipeg, Canada, noticed that the infants of many mammal species have similar distress calls: simple sounds with few changes in pitch. She decided to test whether cross-species responses occur more widely across the evolutionary tree. So, Lingle and her colleague Tobias Riede, now at Midwestern University in Glendale, Arizona, recorded the calls made by infants from a variety of mammal species when separated from their mother or otherwise threatened. They then played the recordings through hidden speakers to wild mule deer (Odocoileus hemionus) out on the Canadian prairies. They found that deer mothers quickly moved towards the recordings of infant deer, but also towards those of infant fur seals, dogs, cats and humans, all of which call at roughly the same pitch. Even the ultrasonic calls of infant bats attracted the deer mothers if Lingle used software to lower their pitch to match that of deer calls. In contrast, they found the deer did not respond to non-infant calls such as birdsong or the bark of a coyote (American Naturalist, DOI: 10.1086/677677). © Copyright Reed Business Information Ltd.
by Rachel Ehrenberg Eating artificial sweeteners may spur the very health problems that dieters try to avoid. A new multipronged study of mice and a small number of people finds that saccharin meddles with the gut’s microbial community, setting in motion metabolic changes that are associated with obesity and diabetes. Other zero-calorie sweeteners may cause the same problems, researchers say September 17 in Nature. Though the finding is preliminary, four of seven human volunteers eating a diet high in saccharin developed impaired glucose metabolism, a warning sign for type 2 diabetes. “This is very interesting and scary if it really does hold for humans,” says Robert Margolskee of the Monell Chemical Senses Center in Philadelphia, who was not involved with the work. “There could be unintended consequences of these artificial sweeteners.” Until recently, most sugar substitutes were thought to pass through the gut undigested, exerting little to no effect on intestinal cells. As ingredients in diet soda, sugar-free desserts and a panoply of other foods, the sweeteners are touted as a way for people with diabetes and weight problems to enjoy a varied diet. But the new study, led by computational biologist Eran Segal and immunologist Eran Elinav of the Weizmann Institute of Science in Rehovot, Israel, suggests that rather than helping people, the sweeteners may promote problems. © Society for Science & the Public 2000 - 2014.
By JOSHUA A. KRISCH PHILADELPHIA — McBaine, a bouncy black and white springer spaniel, perks up and begins his hunt at the Penn Vet Working Dog Center. His nose skims 12 tiny arms that protrude from the edges of a table-size wheel, each holding samples of blood plasma, only one of which is spiked with a drop of cancerous tissue. The dog makes one focused revolution around the wheel before halting, steely-eyed and confident, in front of sample No. 11. A trainer tosses him his reward, a tennis ball, which he giddily chases around the room, sliding across the floor and bumping into walls like a clumsy puppy. McBaine is one of four highly trained cancer detection dogs at the center, which trains purebreds to put their superior sense of smell to work in search of the early signs of ovarian cancer. Now, Penn Vet, part of the University of Pennsylvania’s School of Veterinary Medicine, is teaming with the university’s chemistry and physics departments to isolate cancer chemicals that only dogs can smell. They hope this will lead to the manufacture of nanotechnology sensors that are capable of detecting bits of cancerous tissue 1/100,000th the thickness of a sheet of paper. “We don’t ever anticipate our dogs walking through a clinic,” said the veterinarian Dr. Cindy Otto, the founder and executive director of the Working Dog Center. “But we do hope that they will help refine chemical and nanosensing techniques for cancer detection.” Since 2004, research has begun to accumulate suggesting that dogs may be able to smell the subtle chemical differences between healthy and cancerous tissue, including bladder cancer, melanoma and cancers of the lung, breast and prostate. But scientists debate whether the research will result in useful medical applications. © 2014 The New York Times Company
Keyword: Chemical Senses (Smell & Taste)
Link ID: 20063 - Posted: 09.11.2014
By Lesley Evans Ogden Humans are noisy creatures, our cacophony of jet engines and jackhammering drowning out the communications of other species. In response, a number of animals, including marmosets and whales, turn up their own volume to be heard above the din, a phenomenon called the Lombard effect. A new study reveals that even fish “shout.” Researchers took a close look at the blacktail shiner (Cyprinella venusta), which is common to freshwater streams of the southeastern United States and whose short-distance acoustic signals are often exposed to boat and road noise. Only male shiners make sounds; popping sounds called knocks are used aggressively toward other males, while staticky-sounding “growls” are used for courtship, both heard in the above video. When the scientists brought the fish back to the lab and cranked up white noise from an underwater amplifier, they found that shiner males emitted fewer, shorter pulses, and cranked up the volume of their acoustic signals to be heard above background noise. Published in Behavioral Ecology, it’s the first study documenting the Lombard effect in fish, suggesting that freshwater fish are another group potentially impacted by our ever-increasing hubbub. © 2014 American Association for the Advancement of Science
By JOHN ROGERS LOS ANGELES (AP) — The founder of a Los Angeles-based nonprofit that provides free music lessons to low-income students from gang-ridden neighborhoods began to notice several years ago a hopeful sign: Kids were graduating high school and heading off to UCLA, Tulane and other big universities. That’s when Margaret Martin asked how the children in the Harmony Project were beating the odds. Researchers at Northwestern University in Illinois believe that the students’ music training played a role in their educational achievement, helping as Martin noticed 90 percent of them graduate from high school while 50 percent or more didn’t from those same neighborhoods. A two-year study of 44 children in the program shows that the training changes the brain in ways that make it easier for youngsters to process sounds, according to results reported in Tuesday’s edition of The Journal of Neuroscience. That increased ability, the researchers say, is linked directly to improved skills in such subjects as reading and speech. But, there is one catch: People have to actually play an instrument to get smarter. They can’t just crank up the tunes on their iPod. Nina Kraus, the study’s lead researcher and director of Northwestern’s auditory neuroscience laboratory, compared the difference to that of building up one’s body through exercise. ‘‘I like to say to people: You’re not going to get physically fit just watching sports,’’ she said.
|By Jill U. Adams Our noses are loaded with bitter taste receptors, but they're not helping us taste or smell lunch. Ever since researchers at the University of Iowa came to this conclusion in 2009, scientists have been looking for an explanation for why the receptors are there. One speculation is that they warn us of noxious substances. But they may play another role too: helping to fight infections. In addition to common bitter compounds, the nose's bitter receptors also react to chemicals that bacteria use to communicate. That got Noam Cohen, a University of Pennsylvania otolaryngologist, wondering whether the receptors detect pathogens that cause sinus infections. In a 2012 study, his team found that bacterial chemicals elicited two bacteria-fighting responses in cells from the nose and upper airways: movement of the cells' projections that divert noxious things out of the body and release of nitric oxide, which kills bacteria. The findings may have clinical applications. When Cohen recently analyzed bitter taste receptor genes from his patients with chronic sinus infections, he noticed that practically none were supertasters, even though supertasters make up an estimated 25 percent of the population. Supertasters are extra sensitive to bitter compounds in foods. People are either supertasters or nontasters, or somewhere in between, reflecting the genes they carry for a receptor known as T2R38. Cohen thinks supertasters react vigorously to bacterial bitter compounds in the nose and are thus resistant to sinus infections. In nontasters the reaction is weaker, bacteria thrive and sinus infections ensue. These results suggest that a simple taste test could be used to predict who is at risk for recurrent infections and might need more aggressive medical treatment. © 2014 Scientific American
by Jennifer Viegas Spritzing dogs with a “pig perfume” helps prevent them from barking incessantly, jumping frantically on house guests and from engaging in other unwanted behaviors, according to new research. The eau de oink, aka “Boar Mate” or “Stop That,” was formulated by Texas Tech scientist John McGlone, who was looking for a way to curb his Cairn terrier Toto’s non-stop barking. One spritz of the pig perfume seemed to do the trick in an instant without harming his dog. “It was completely serendipitous,” McGlone, who works in the university’s Animal and Food Sciences department of the College of Agriculture and Natural Sciences, said in a press release. “One of the most difficult problems is that dogs bark a lot, and it’s one of the top reasons they are given back to shelters or pounds.” The key ingredient is androstenone, a steroid and pheromone produced by male pigs and released in their saliva and fat. When detected by female pigs in heat, they seem to find the male more attractive. (The females assume a mating stance.) One can imagine that dogs spritzed with the scent should not hang around amorous female pigs, but other than that, the product seems to work, according to McGlone. Androstenone smells pungent and is not very appealing to humans, but it can have an effect on mammal behavior, he said. © 2014 Discovery Communications, LLC.
Keyword: Chemical Senses (Smell & Taste)
Link ID: 19994 - Posted: 08.26.2014
by Philippa Skett It's the strangest sweet tooth in the world. Birds lost the ability to taste sugars, but nectar-feeding hummingbirds re-evolved the capacity by repurposing receptors used to taste savoury food. To differentiate between tastes, receptors on the surface of taste buds on the tongue, known as T1Rs, bind to molecules in certain foods, triggering a neurological response. In vertebrates such as humans, a pair of these receptors – T1R2 and T1R3 – work together to deliver the sweet kick we experience from sugar. But Maude Baldwin at Harvard University and her colleagues found that birds don't have the genes that code for T1R2. They are found in lizards, though, suggesting that they were lost at some point during the evolution of birds or the dinosaurs they evolved from. But hummingbirds clearly can detect sugar: not only do they regularly sup on nectar, taste tests show they prefer sweet tasting foods over blander options. Now Baldwin and her team have worked out why: another pair of receptors – T1R1 and T1R3 – work together to detect sugar. Other vertebrates use T1R1 to taste savoury foods. It seems that in hummingbirds the proteins on the surface of the two receptors have been modified so that they respond to sugars instead. © Copyright Reed Business Information Ltd.