Chapter 9. Hearing, Vestibular Perception, Taste, and Smell
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By Cat Bohannon Halos, auras, flashes of light, pins and needles running down your arms, the sudden scent of sulfur—many symptoms of a migraine have vaguely mystical qualities, and experts remain puzzled by the debilitating headaches' cause. Researchers at Harvard University, however, have come at least one step closer to figuring out why women are twice as likely to suffer from chronic migraines as men. The brain of a female migraineur looks so unlike the brain of a male migraineur, asserts Harvard scientist Nasim Maleki, that we should think of migraines in men and women as “different diseases altogether.” Maleki is known for looking at pain and motor regions in the brain, which are known to be unusually excitable in migraine sufferers. In one notable study published in the journal Brain last year, she and her colleagues exposed male and female migraineurs to painful heat on the backs of their hands while imaging their brains with functional MRI. She found that the women had a greater response in areas of the brain associated with emotional processing, such as the amygdala, than did the men. Furthermore, she found that in these women, the posterior insula and the precuneus—areas of the brain responsible for motor processing, pain perception and visuospatial imagery—were significantly thicker and more connected to each other than in male migraineurs or in those without migraines. In Maleki's most recent work, presented in June at the International Headache Congress, her team imaged the brains of migraineurs and healthy people between the ages of 20 and 65, and it made a discovery that she characterizes as “very, very weird.” In women with chronic migraines, the posterior insula does not seem to thin with age, as it does for everyone else, including male migraineurs and people who do not have migraines. The region starts thick and stays thick. © 2013 Scientific American
Alice Roberts It's the rutting season. From Richmond Park to the Isle of Rum, red deer hinds will be gathering, and the stags that have spent the past 10 months minding their own business in bachelor groups are back in town, with one thing on their minds. A mature male that has netted himself a harem is very dedicated. He practically stops eating, focusing instead on keeping his hinds near and his competitors at bay. If you're a red deer stag, one of the ways you make sure that your adversaries know you mean business – and that you're big – is roaring. And you don't let up. You can keep roaring all day, and through the night too, twice a minute, if necessary. While female red deer prefer the deeper roars of larger stags, roaring also appears to be part of how stags size one another up, before deciding whether or not to get engaged in a full-on physical fight. Most confrontations are settled without locking antlers. In male red and fallow deer, the voicebox or larynx is very low in the throat – and gets even lower when they roar. Strap-like muscles that attach to the larynx contract to drag it down towards the breastbone – lengthening the vocal tract and deepening the stag's roar. Deepening the voice exaggerates body size. Over generations, stags with deeper roars presumably had more reproductive success, so the position of the larynx moved lower and lower in the neck. When a red deer stag roars his larynx is pulled down so far that it contacts the front of his breastbone – it couldn't get any lower. In human evolution, much is made of the low position of the larynx in the neck. So much, in fact, that it has been considered to be a uniquely human trait, and intrinsically linked to that other uniquely human trait: spoken language. But if red and fallow deer also have low larynges, that means, first, that we're not as unusual as we like to think we are, and second, that there could be other reasons – that are nothing to do with speaking – for having a descended larynx. © 2013 Guardian News and Media Limited
by Laura Sanders When I started to get out and about with Baby V, I occasionally experienced a strange phenomenon. Women would approach and coo some pleasant little noises. After an appropriate amount of time had passed, these strangers would lean in close and ask to smell my baby. I’m the first to admit that this sounds creepy. Truth be told, it is a little creepy. But now I completely get it. The joy from a single whiff of newborn far outweighs any trifling social conventions about personal space and body odors. So when women approach looking for a little hit of eau de bebe, I get sharey. By all means, ladies, lean in and smell away. Tiny babies smell very, very good. So good that I’m getting a little high from just thinking about how good babies smell. So good that people attempt to bottle and sell this scent (like this baby-head-scented spray— pleasant, but pales in comparison). So good that scientists really want to know why some women find this smell irresistible. Scientists recently studied the brains of women as they sniffed new baby scent. Two-day-old babies delivered the good stuff by wearing the same pajamas for two nights. Women then sniffed the odor extracted from the outfit while brain scans assessed neural activity. Overall, the 30 women in the study (who weren’t told what they were sniffing, by the way) rated the scent as mildly pleasant. As the intoxicating scent of newborn wafted into their brains, neural activity increased in areas of the brain linked to good feelings, called neostriate areas. In the brains of the 15 women who also happened to be mothers, the brain activity seemed stronger. (No word yet on what new baby smell does to dads’ brains.) © Society for Science & the Public 2000 - 2013.
By Julianne Wyrick Some people are drawn to the thick smell of bacon, sizzling and crackling in the skillet on a Saturday morning. For others, it’s the aroma of freshly baked cookies on a Friday night or the smell of McDonald’s fries creeping in through the car window. At this time of year, I find the scent of freshly baked pumpkin muffins irresistible. Of course, I’d like to think I’m not a slave to my nose, at least not when I’m nice and full from dinner. If I were a fruit fly, my outlook might not be so good. Already-fed fruit fly larvae exposed to certain food-related odors ate more food than larvae that didn’t experience the smells, according to research published by scientists at the University of Georgia last spring. “They’re not hungry, but they will get an extra kick in terms of appetite, so they will eat, for example, 30 percent extra,” said Ping Shen, lead author on the study. The scents, which included the sweet odor of bananas or the sharper smell of balsamic vinegar, served as “cues” or triggers that the flies associated with food. The triggers motivated the fly larvae to eat, even when they’d already had dinner. That doesn’t bode so well for flies trying to watch their weight. For the fly to feel this urge to eat, the smell has to be transported from sensory receptors in the nose to the part of the brain that regulates appetite—the brain’s “feeding center”—via a series of neurons. Part of this signal transfer involves dopamine, a neurotransmitter associated with behavior motivated by a cue or hint of something to come, like smells associated with food. © 2013 Scientific American
Heather Saul Stress can make the world around us smell unpleasant, the results of a new study are suggesting. Researchers from the University of Wisconsin-Madison used powerful brain imaging technologies to examine how stress and anxiety "re-wire" the brain. A team of psychologists led by Professor Wen Li discovered that when a person experiences stress, emotion systems and olfactory processing in the brain become linked, making inoffensive smells become unpleasant. Although the emotion and olfactory systems within the brain are usually found next to each other, there is rarely 'crosstalk' between the two. Writing in the Journal of Neuroscience, Prof Li said results from their research will now help to uncover the biological mechanisms at work when a person feels stressed. Using functional MRI scans, the team analysed the brain activity of 12 participants after showing them images designed to induce anxiety as they smelled familiar, neutral odours. The subjects were then asked to rate the different smells before being shown the disturbing image and afterwards. The majority showed a more negative response to odours that they had previously considered neutral. This fuels a 'feedback loop' that heightens distress, and can even lead to clinical issues such as depression. Prof Li explained: "After anxiety induction, neutral smells become clearly negative." “In typical odor processing, it is usually just the olfactory system that gets activated,” says Li. “But when a person becomes anxious, the emotional system becomes part of the olfactory processing stream. © independent.co.uk
Ballet dancers develop differences in their brain structures to allow them to perform pirouettes without feeling dizzy, a study has found. A team from Imperial College London said dancers appear to suppress signals from the inner ear to the brain. Dancers traditionally use a technique called "spotting", which minimises head movement. The researchers say their findings may help patients who experience chronic dizziness. Dizziness is the feeling of movement when, in reality, you are still. For most it is an occasional, temporary sensation. But around one person in four experiences chronic dizziness at some point in their life. When someone turns or spins around rapidly, fluid in the vestibular organs of the inner ear can be felt moving through tiny hairs. Once they stop, the fluid continues to move, which can make a person feel like they are still spinning. Ballet dancers train hard to be able to spin, or pirouette, rapidly and repeatedly. They use a technique called spotting, focusing on a spot on the floor - as they spin, their head should be the last bit to move and the first to come back. In the study, published in the journal Cerebral Cortex, the team recruited 29 female ballet dancers and 20 female rowers of similar age and fitness levels. BBC © 2013
Link ID: 18709 - Posted: 09.28.2013
By PETER ANDREY SMITH In a cavernous basement laboratory at the University of Minnesota, Thomas Stoffregen thrusts another unwitting study subject — well, me — into the “moving room.” The chamber has a concrete floor and three walls covered in faux marble. As I stand in the middle, on a pressure sensitive sensor about the size of a bathroom scale, the walls lurch inward by about a foot, a motion so disturbing that I throw up my arms and stumble backward. Indeed, the demonstration usually throws adults completely off balance. I’m getting off lightly. Dr. Stoffregen, a professor of kinesiology, uses the apparatus to study motion sickness, and often subjects must stand and endure subtle computer-driven oscillations in the walls until they are dizzy and swaying. Dr. Stoffregen’s research has also taken him on cruises — cruise ships are to motion sickness what hospitals are to pneumonia. “No one’s ever vomited in our lab,” he said. “But our cruises are a different story.” For decades now, Dr. Stoffregen, 56, director of the university’s Affordance Perception-Action Laboratory, has been amassing evidence in support of a surprising theory about the causes of motion sickness. The problem does not arise in the inner ear, he believes, but rather in a disturbance in the body’s system for maintaining posture. The idea, once largely ignored, is beginning to gain grudging recognition. “Most theories say when you get motion sick, you lose your equilibrium,” said Robert Kennedy, a psychology professor at the University of Central Florida. “Stoffregen says because you lose your equilibrium, you get motion sick.” Motion sickness is probably a problem as old as passive transportation. The word “nausea” derives from the Greek for “boat,” but the well-known symptoms arise from a variety of stimuli: lurching on the back of a camel, say, or riding the Tilt-a-Whirl at a fair. “Pandemonium,” the perpetually seasick Charles Darwin called it. Copyright 2013 The New York Times Company
By Michelle Roberts Health editor, BBC News online The thousands of aromas humans can smell can be sorted into 10 basic categories, US scientists say. Prof Jason Castro, of Bates College, and Prof Chakra Chennubhotla, of the University of Pittsburgh, used a computerised technique to whittle down smells to their most basic essence. They told the PLoS One journal they had then tested 144 of these and found they could be grouped into 10 categories. The findings are contentious - some say there are thousands of permutations. Prof Castro said: "You have these 10 basic categories because they reflect important attributes about the world - danger, food and so on. "If you know these basic categories, then you can start to think about building smells. "We have not solved the problem of predicting a smell based on its chemical structure, but that's something we hope to do." He said it would be important to start testing the theory on more complex aromas, such as perfumes and everyday smells. In reality, any natural scent was likely to be a complex mix - a blend of the 10 different categories, he said. Prof Tim Jacob, a UK expert in smell science at Cardiff University, said: "In the 1950s a scientist called John Amoore proposed a theory which involved seven smell categories based upon molecular shape and size. BBC © 2013
Keyword: Chemical Senses (Smell & Taste)
Link ID: 18671 - Posted: 09.19.2013
Amanda Fiegl What's the difference between a spicy meal and being tickled? Not much, from your lips' perspective. A new study reports that Szechuan pepper activates the same nerves that respond to a light physical touch. Researchers at the University College London Institute of Cognitive Neuroscience found that people experienced the same sensation when either Szechuan pepper—a spice used in many types of Asian cuisine—or a machine vibrating at a particular frequency was placed on their lips. "The pepper is sending the same information to the brain as having a buzzer on your lips," the study's lead author, Nobuhiro Hagura, said in an email. The study, published today in Proceedings of the Royal Society B with the wry headline "Food Vibrations," delves into the little-known field of psychophysics, which "describes the relation between physical reality and what we actually perceive," Hagura said. "Our research shows just one interesting example of a case where we perceive something quite different than what is actually there," he said. "In many cases, the difference between perception and reality can be explained by understanding how the nervous system transmits information about the outside world to the brain." Previous studies have shown that other spicy ingredients, such as chili peppers and mustard oils, activate the nerve fibers associated with pain and physical heat. And studies in animals indicated that the spicy chemical in Szechuan pepper—sanshool—acts on the nervous system's "light touch" fibers. So Hagura and his colleagues wanted to find out whether sanshool produces a conscious sensation of touch in humans. © 1996-2013 National Geographic Society.
By Bruce Bower Babies have an ear for primeval dangers, a new study suggests. By age 9 months, infants pay special attention to sounds that have signaled threats to children’s safety and survival throughout human evolution, say psychologist Nicole Erlich of the University of Queensland, Australia, and her colleagues. Those sounds include a snake hissing, adults’ angry voices, a crackling fire, thunder claps and — as a possible indicator of a nearby but unseen danger — another infant’s cries. Noises denoting modern dangers, as well as pleasant sounds, failed to attract the same level of interest from 9-month-olds, Erlich and her colleagues report Aug. 27 in Developmental Science. People can learn to fear just about anything. But tens of thousands of years of evolution have primed infants’ brains to home in on longstanding perils, the scientists propose. “There is something special about evolutionarily threatening sounds that infants respond to,” Erlich says. Another study that supported that idea, by psychologist David Rakison of Carnegie Mellon University in Pittsburgh, found that 11-month-olds rapidly learn to associate fearful faces with images of snakes and spiders (SN: 9/26/09, p. 11). “There is now a coherent argument that infants are biologically prepared in at least two sensory systems to learn quickly which evolutionarily relevant objects to fear,” Rakison says. © Society for Science & the Public 2000 - 2013
Two pioneers in the study of neural signaling and three researchers responsible for modern cochlear implants are winners of The Albert and Mary Lasker Foundation’s annual prize, announced today. The prestigious award honoring contributions in the medical sciences is often seen as a hint at future Nobel contenders. The prizes for basic and clinical research each carry a $250,000 honorarium. Richard Scheller of the biotech company Genentech and Thomas Südhof of Stanford University in Palo Alto, California, got their basic research Laskers for discovering the mechanisms behind rapid the release of neurotransmitters—the brain’s chemical messengers—into the space between neurons. This process underlies all communication among brain cells, and yet it was “a black box” before Scheller and Südhof’s work, says their colleague Robert Malenka, a synaptic physiologist at Stanford. The two worked independently in the late 1980s to identify individual proteins that mediate the process, and their development of genetically altered mice lacking these proteins was “an ambitious and high-risk approach,” Malenka says. Although “they weren’t setting out to understand any sort of disease,” their discoveries have helped unravel the genetic basis for neurological disorders such as Parkinson’s disease. This year’s clinical research prizes went to Graeme Clark, Ingeborg Hochmair, and Blake Wilson for their work to restore hearing to the deaf. In the 1970s, Hochmair and Clark of the cochlear implant company MED-EL in Innsbruck, Austria, and the University of Melbourne, respectively, were the first to insert multiple electrodes into the human cochlea to stimulate nerves that respond to different frequencies of sound. © 2012 American Association for the Advancement of Science
by Jon White Ever tried beetroot custard? Probably not, but your brain can imagine how it might taste by reactivating old memories in a new pattern. Helen Barron and her colleagues at University College London and Oxford University wondered if our brains combine existing memories to help us decide whether to try something new. So the team used an fMRI scanner to look at the brains of 19 volunteers who were asked to remember specific foods they had tried. Each volunteer was then given a menu of 13 unusual food combinations – including beetroot custard, tea jelly, and coffee yoghurt – and asked to imagine how good or bad they would taste, and whether or not they would eat them. "Tea jelly was popular," says Barron. "Beetroot custard not so much." When each volunteer imagined a new combination, they showed brain activity associated with each of the known ingredients at the same time. It is the first evidence to suggest that we use memory combination to make decisions, says Barron. Journal reference: Nature Neuroscience, doi: 10.1038/nn.3515 © Copyright Reed Business Information Ltd.
By Josh Shaffer DURHAM It’s not often that the high-minded world of neuroscience collides with the corny, old-fashioned art of ventriloquism. One depends on dummies; the other excludes them. But a Duke University study uses puppet-based comedy to demonstrate the complicated inner workings of the brain and shows what every ventriloquist knows: The eye is more convincing than the ear. The study, which appears in the journal PLOS ONE, seeks to explain how the brain combines information coming from two different senses. How, asks Duke psychology and neuroscience professor Jennifer Groh, does the brain determine where a sound is coming from? In your eyes, the retina takes a snapshot, she said. It makes a topographic image of what’s in front of you. But the ears have nothing concrete to go on. They have to rely on how loud the sound is, how far away and from what direction. That’s where a ventriloquist comes in, providing a model for this problem. With a puppet, the noise and the movement are coming from different places. So how does the brain fix this and choose where to look? Duke researchers tested their hypotheses on 11 people and two monkeys, placing them in a soundproof booth.
By Tamar Haspel, American eaters love a good villain. Diets that focus on one clear bad guy have gotten traction even as the bad guy has changed: fat, carbohydrates, animal products, cooked food, gluten. And now Robert Lustig, a pediatric endocrinologist at the University of California at San Francisco, is adding sugar to the list. His book “ Fat Chance: Beating the Odds Against Sugar, Processed Food, Obesity, and Disease ” makes the case that sugar is almost single-handedly responsible for Americans’ excess weight and the illnesses that go with it. “Sugar is the biggest perpetrator of our current health crisis,” says Lustig, blaming it for not just obesity and diabetes but also for insulin resistance, cardiovascular disease, stroke, even cancer. “Sugar is a toxin,” he says. “Pure and simple.” His target is one particular sugar: fructose, familiar for its role in making fruit sweet. Fruit, though, is not the problem; the natural sugar in whole foods, which generally comes in small quantities, is blameless. The fructose in question is in sweeteners — table sugar, high-fructose corn syrup, maple syrup, honey and others — which are all composed of the simple sugars fructose and glucose, in about equal proportions. Although glucose can be metabolized by every cell in the body, fructose is metabolized almost entirely by the liver. There it can result in the generation of free radicals ( damaged cells that can damage other cells) and uric acid ( which can lead to kidney disease or gout ), and it can kick off a process called de novo lipogenesis, which generates fats that can find their way into the bloodstream or be deposited on the liver itself. These byproducts are linked to obesity, insulin resistance and the group of risk factors linked to diabetes, heart disease and stroke. (Lustig gives a detailed explanation of fructose metabolism in a well-viewed YouTube video called “Sugar: The Bitter Truth.”) © 1996-2013 The Washington Post
By Caitlin Kirkwood Do NOT EAT the chemicals. It is the #1 laboratory safety rule young scientists learn to never break and for good reason; it keeps lab citizens alive and unscathed. However, if it hadn’t been for the careless, rule-breaking habits of a few rowdy scientists ingesting their experiments, many artificial sweeteners may never have been discovered. Perhaps the strangest anecdote for artificial sweetener discovery, among tales of inadvertent finger-licking and smoking, is that of graduate student Shashikant Phadnis who misheard instructions from his advisor to ‘test’ a compound and instead tasted it. Rather than keeling over, he identified the sweet taste of sucralose, the artificial sweetener commonly known today as Splenda. Artificial sweeteners like Splenda, Sweet’N Low, and Equal provide a sweet taste without the calories. Around World War II, in response to a sugar shortage and evolving cultural views of beauty, the target consumer group for noncaloric sweetener manufacturers shifted from primarily diabetics to anyone in the general public wishing to reduce sugar intake and lose weight. Foods containing artificial sweeteners changed their labels. Instead of cautioning ‘only for consumption by those who must restrict sugar intake’, they read for those who ‘desire to restrict’ sugar. Today, the country is in the middle of a massive debate about the health implications of artificial sweeteners and whether they could be linked to obesity, cancer, and Alzheimer disease. It’s a good conversation to have because noncaloric sweeteners are consumed regularly in chewing gums, frozen dinners, yogurts, vitamins, baby food, and particularly in diet sodas. © 2013 Scientific American
Inner-ear problems could be a cause of hyperactive behaviour, research suggests. A study on mice, published in Science, said such problems caused changes in the brain that led to hyperactivity. It could lead to the development of new targets for behaviour disorder treatments, the US team says. A UK expert said the study's findings were "intriguing" and should be investigated further. Behavioural problems such as ADHD are usually thought to originate in the brain. But scientists have observed that children and teenagers with inner-ear disorders - especially those that affect hearing and balance - often have behavioural problems. However, no causal link has been found. The researchers in this study suggest inner-ear disorders lead to problems in the brain which then also affect behaviour. The team from the Albert Einstein College of Medicine of Yeshiva University in New York noticed some mice in the lab were particularly active - constantly chasing their tails. They were found to be profoundly deaf and have disorders of the inner ear - of both the cochlea, which is responsible for hearing, and the vestibular system, which is responsible for balance. The researchers found a mutation in the Slc12a2 gene, also found in humans. Blocking the gene's activity in the inner ears of healthy mice caused them to become increasingly active. BBC © 2013
By Bruce Bower Strange things happen when bad singers perform in public. Comedienne Roseanne Barr was widely vilified in 1990 after she screeched the national anthem at a major league baseball game. College student William Hung earned worldwide fame and a recording contract in 2004 with a tuneless version of Ricky Martin’s hit song “She Bangs” on American Idol. Several singers at karaoke bars in the Philippines have been shot to death by offended spectators for mangling the melody of Frank Sinatra’s “My Way.” For all the passion evoked by pitch-impaired vocalists, surprisingly little is known about why some people are cringe-worthy crooners. But now a rapidly growing field of research is beginning to untangle the mechanics of off-key singing. The new results may improve scientists’ understanding of how musical abilities develop and help create a toolbox of teaching strategies for aspiring vocalists. Glimpses are also emerging into what counts as “in tune” to the mind’s ear. It seems that listeners are more likely to label stray notes as in tune when those notes are sung as opposed to played on a violin. Running through this new wave of investigations is a basic theme: There is one way to carry a tune and many ways to fumble it. “It’s kind of amazing that any of us can vocally control pitch enough to sing well,” says psychologist Peter Pfordresher of the University at Buffalo, New York. Still, only about 10 percent of adults sing poorly, several reports suggest (although some researchers regard that figure as an underestimate). Some of those tune-challenged crooners have tone deafness, a condition called amusia, which afflicts about 4 percent of the population. Genetic and brain traits render these folks unable to tell different musical notes apart or to recognize a tune as common as “Happy Birthday.” Amusia often — but curiously, not always — results in inept singing. Preliminary evidence suggests that tone-deaf individuals register pitch changes unconsciously, although they can’t consciously decide whether one pitch differs from another. © Society for Science & the Public 2000 - 2013
Link ID: 18612 - Posted: 09.07.2013
Elizabeth Pennisi Dolphins and bats don't have much in common, but they share a superpower: Both hunt their prey by emitting high-pitched sounds and listening for the echoes. Now, a study shows that this ability arose independently in each group of mammals from the same genetic mutations. The work suggests that evolution sometimes arrives at new traits through the same sequence of steps, even in very different animals. The research also implies that this convergent evolution is common—and hidden—within genomes, potentially complicating the task of deciphering some evolutionary relationships between organisms. Nature is full of examples of convergent evolution, wherein very distantly related organisms wind up looking alike or having similar skills and traits: Birds, bats, and insects all have wings, for example. Biologists have assumed that these novelties were devised, on a genetic level, in fundamentally different ways. That was also the case for two kinds of bats and toothed whales, a group that includes dolphins and certain whales, that have converged on a specialized hunting strategy called echolocation. Until recently, biologists had thought that different genes drove each instance of echolocation and that the relevant proteins could change in innumerable ways to take on new functions. But in 2010, Stephen Rossiter, an evolutionary biologist at Queen Mary, University of London, and his colleagues determined that both types of echolocating bats, as well as dolphins, had the same mutations in a particular protein called prestin, which affects the sensitivity of hearing. Looking at other genes known to be involved in hearing, they and other researchers found several others whose proteins were similarly changed in these mammals. © 2012 American Association for the Advancement of Science
by Jennifer Viegas Goldfish not only listen to music, but they also can distinguish one composer from another, a new study finds. The paper adds to the growing body of evidence that many different animals understand music. For the study, published in the journal Behavioural Processes, Shinozuka and colleagues Haruka Ono and Shigeru Watanabe played two pieces of classical music near goldfish in a tank. The pieces were Toccata and Fugue in D minor by Johann Sebastian Bach and The Rite of Spring by Igor Stravinsky. The scientists trained the fish to gnaw on a little bead hanging on a filament in the water. Half of the fish were trained with food to gnaw whenever Bach played and the other half were taught to gnaw whenever Stravinsky music was on. The goldfish aced the test, easily distinguishing the two composers and getting a belly full of food in the process. The fish were more interested in the vittles than the music, but earlier studies on pigeons and songbirds suggest that Bach is the preferred choice, at least for birds. “These pieces can be classified as classical (Bach) and modern (Stravinsky) music,” Shinozuka explained. “Previously we demonstrated that Java sparrows preferred classical over modern music. Also, we demonstrated Java sparrows could discriminate between consonance and dissonance.” © 2013 Discovery Communications, LLC.
by Michael Marshall Life is tough when you're small. It's not just about getting trodden on by bigger animals. Some of the tiniest creatures struggle to make their bodies work properly. This leads to problems that us great galumphing humans will never experience. For instance, the smallest frogs are prone to drying out because water evaporates so quickly from their skin. Miniature animals can't have many offspring, because there is no room in their bodies to grow them. One tiny spider has even had to let its brain spill into its legs, because its head is too small to accommodate it. Gardiner's Seychelles frog is one of the smallest vertebrates known to exist, at just 11 millimetres long. Its tiny head is missing parts of its ears, which means it shouldn't be able to hear anything. It can, though, and that is thanks to its big mouth. One of only four species in the genus Sechellophryne, Gardiner's Seychelles frog is a true rarity. It is confined to a few square kilometres of two islands in the Seychelles, and even if you visit its habitat you're unlikely to see it. That's because the frog spends most of its time in moist leaf litter, so that it doesn't dry out. It eats tiny insects and other invertebrates. When it comes to hearing, it is sadly under-equipped. Unlike most frogs, it doesn't have an external eardrum. Inside its head, it does have the amphibian equivalent of a cochlea, which is the bit that actually detects sounds. But it doesn't have a middle ear to transmit the sound to the cochlea, and is also missing a bone called the columella that would normally help carry the sound. © Copyright Reed Business Information Ltd.