Gustation and Olfaction The Senses of Taste and Smell Why do we study taste and smell together? SENSORY INTERACTION: the principle that one sense may influence another. The senses of taste and smell have a very cooperative working relationship. Many of the subtle distinctions you may think of as flavors really come from odors (Much of the “taste” of an onion is odor, not flavor). Often, if you can’t smell the food, you can’t taste the food (have you tried eating when you have a bad cold?) Gustation – The Sense of Taste What is the central muscle involved in taste? Five Distinct Tastes Sweet Sour Bitter Salty Umami (the taste of glutamate (MSG) – savory taste in meat and cheese) Each of these tastes developed as survival functions, according to evolutionary psychology. Sweet - energy source Sour – potentially toxic acid Bitter – potential poisons Salty – sodium essential to physiological processes Umami – proteins to grow and repair tissue A Theory Debunked Since 1942, tongue maps like this one were widely published and touted as an accurate portrayal of where certain taste receptors were located. Wine glasses are even designed around this idea. The notion that the tongue is mapped into four areas—sweet, sour, salty and bitter—is wrong. There are five basic tastes identified so far, and the entire tongue can sense all of these tastes more or less equally. The tongue map is easy enough to prove wrong at home. Place salt on the tip of your tongue. You'll taste salt. For reasons unknown, scientists never bothered to dispute this inconvenient truth until 1974, and even today, many textbooks still publish picures of the tongue map. Remarkably, more is known about vision and hearing, far more complicated senses, than taste. Papillae Those bumps on our tongue are called papillae. Papillae help grip food while your teeth are chewing. They also have another special job - they contain your taste buds Grab a partner and identify some papillae – how many do you see? Count them and write the number down. Individuals vary in their sensitivity to taste sensations, a function of the density of these papillae on the tongue. Taste Buds Taste (gustation) has as its physical stimulus chemical substances that are dissolvable in water. Receptors for taste are clusters of cells found in the taste buds, which line the trenches around tiny bumps on the tongue. These cells absorb chemicals, trigger neural impulses, and send the information throughout the thalamus and on to the somatosensory cortex in the parietal lobe. Figure 4.49: The tongue and taste. (a) Taste buds line the trenches around tiny bumps on the tongue called papillae. There are three types of papillae, which are distributed on the tongue as shown in (b). The taste buds found in each type of papillae show slightly different sensitivities to the four basic tastes, as mapped out in the graph at the top. Thus, sensitivity to the primary tastes varies across the tongue, but these variations are small, and all four primary tastes can be detected wherever there are taste receptors. (Data adapted from Bartoshuck 1993a). Other Taste Facts Taste receptors reproduce themselves every week or two (this is why it hardly matters if you burn your tongue with hot food). As you grow older, the number of taste buds decreases, as does taste sensitivity. As with other senses, your expectations influence your brain’s response. If you are told something is going to taste bad, your brain responds more negatively. Likewise, being told that a wine costs $90 rather than its real $10 price makes an inexpensive wine taste better and triggers more activity in a brain area that responds to pleasant experiences. As happens with the pain placebo effect, the brain’s thinking frontal lobes offer information that other brain regions act upon. Non-Tasters, Tasters, and Supertasters In 1931, a chemist named Arthur Fox was pouring some powdered PTC (phenylthiocarbamide) into a bottle. When some of the powder accidentally blew into the air, a colleague standing nearby complained that the dust tasted bitter. Fox tasted nothing at all. Curious how they could be tasting the chemical differently, they tasted it again. The results were the same. Fox had his friends and family try the chemical then describe how it tasted. Some people tasted nothing. Some found it intensely bitter, and still others thought it tasted only slightly bitter. The PTC gene, TAS2R38, was discovered in 2003. Soon after its discovery, geneticists determined that there is an inherited component that influences how we taste PTC. Today we know that the ability to taste PTC (or not) is conveyed by a single gene that codes for a taste receptor on the tongue. The ratio of tasters to non-tasters varies between populations, but every group has some tasters and some non-tasters. On average, 75% of people can taste PTC, while 25% cannot. There are two common forms (or alleles) of the PTC gene, and at least five rare forms. One of the common forms is a tasting allele, and the other is a nontasting allele. Each allele codes for a bitter taste receptor protein with a slightly different shape. The shape of the receptor protein determines how strongly it can bind to PTC. Since all people have two copies of every gene, combinations of the bitter taste gene variants determine whether someone finds PTC intensely bitter, somewhat bitter, or without taste at all. The “PTC Gene” The ability to taste PTC shows a dominant pattern of inheritance. A single copy of a tasting allele (T) conveys the ability to taste PTC. Nontasters have two copies of a non-tasting allele (t). Can you taste PTC? Try a PTC strip yourself, and rate the taste on the Green Scale. Now, look back at how many papillae your partner was able to identify in the sample area of your tongue earlier. Supertasters have a mean of 44 Tasters have a mean of 32 Non-tasters have a mean of 24 Does this match up with your PTC paper results? About 25% of the world’s population are supertasters (a higher percentage of women fall into this category), 50% are tasters, and 25% are non-tasters. The world is built for regular tasters that experience food as not too sweet, bitter, salty, or sour. Evolutionary psychologists believe that there are advantages to being a supertaster vs. a non-taster. Super tasters would be able to tell if a plant was poison; non-tasters evolved in times of famine due to needing to eat tree bark, etc. Why does this matter? Studies indicate that individuals with the “strong tasters” PTC gene variant were less likely to be smokers. This may indicate that people who find PTC bitter are more likely than non-tasters to find the taste of cigarettes bitter and may be less likely to smoke. Other studies suggest that there may be correlations between the ability to taste PTC and preferences for certain types of foods. This may be why some of us think that broccoli is just too bitter to eat. Interestingly, supertasters and non-tasters also respond to noise differently. Bartoshuk finds that supertasters may rate a particular noise level as very loud, between a boombox and a baby crying, while non-tasters rate it much lower, PTC tasters may be more sensitive than non-tasters to compounds in between a shout and a boombox. tobacco and vegetables in the cabbage family. Why does this matter? (cont.) If you are a supertaster: You probably cannot stand the taste of broccoli, Brussels sprouts, spinach, diet drinks, cauliflower, rutabaga, strong cheeses, turnips, or bok choy (Chinese cabbage). Caffeine also makes coffee taste bitter to tasters, but has little effect on non-tasters. They perceive more burn from oral irritants, like alcohol and chili peppers. Many foods are too intense. Vegetables are especially unpalatable and so supertasters have an increased risk of colon cancer. The upside of being a supertaster is that fats are also experienced as too intense. Thus, supertasters weight is lower, their blood profile is healthier, and their risk of cardiovascular disease is reduced. If you are a non-taster: You probably do not experience the intensity of foods that others do. Non-tasters tend to like very spicy foods, perhaps because they may be trying to experience some strong tastes. They do not taste the bitterness in heavily alcoholic drinks, so they may have a higher incidence of alcoholism. “Non-tasters live in a pastel taste world, whereas supertasters live in a neon taste world.” Picky Eaters by NOVA Watch the video Picky Eaters by NOVA ScienceNOW. http://www.pbs.org/wgbh/nova/sciencenow/0404/01.html More on the Web! • NOVA scienceNOW’s Tour the Tongue (10 minutes) http://www.pbs.org/wgbh/nova/body/tongue-taste.html Learn how taste works and why we evolved the ability to detect bitter and sweet tastes. • NOVA’s The Sense of Taste (4 minutes) http://www.pbs.org/teachers/connect/resources/888/preview Learn what happens when we lose our sense of taste and how smell affects our experience of food. • Howard Hughes Medical Institute’s Taste Lecture (6 minutes) http://www.hhmi.org/lectures/webcast/ondemand/97webcast1/tast e.html Learn how taste receptors function. (Also check out the other lectures listed at the bottom of this site!) Other Cool Taste Sensations If you decide to try these yourself at home, make sure you check with your parents first! You should make sure to read all about them before trying anything, because they have not necessarily been completely studied. Gymnemia Sylvestre – a taste modifier that selectively abolishes the sensation of sweet, leaving all other taste modalities unchanged. Gymnemia is sold over the counter as a tea in Japan. Can be obtained through Best Nutrition Products at http://www.gymnema.com/ (510-477-9116). Prepare as instructed and store in the fridge. The drink tastes like spinach tea, but it won’t be bad if you hold your nose. You might want to rinse your mouth with water immediately afterward. Taste salt (should taste normal), then sugar (will taste like melting sand on the tongue), Sweet Tarts (will be purely sour), and finally M & M’s (will taste quite bitter). The Miracle Fruit – a plant native to West Africa that makes things taste sweet. It contains miraculin, which binds to the tongue’s taste buds when the fruit is consumed. Miraculin acts as a sweetness inducer when it comes in contact with acids, causing bitter and sour foods to taste sweet, temporarily. This effect usually lasts between 30 minutes and 2 hours. These berries are being used in some places to help treat obesity and make food more appealing to people undergoing chemotherapy. http://www.miraclefruitusa.com/ - this website explains the fruit (watch the video about the foodtasting parties thrown in NY), and sells the berries, tablets, and plants to grow your own. Read an article from the NY Times: http://www.nytimes.com/2008/05/28/dining/28flavor.html?_r=1 From Union County College’s Biology Dept: http://faculty.ucc.edu/biologyombrello/pow/miracle_berry.htm Olfaction Our Sense of Smell How Olfaction Works Smell (Olfaction) operates much like the sense of taste. The physical stimuli are chemical substances carried in the air that are dissolved in fluid, the mucus in the nose. Pathway: Olfactory cilia -> neural impulse -> olfactory nerve -> olfactory bulb (brain) Olfactory receptors are called olfactory cilia and are located in the upper portion of the nasal passages. The olfactory receptors synapse directly with cells in the olfactory bulb at the base of the brain. Olfaction is the only sense, therefore, that is not routed through the thalamus. This suggests that smell evolved earlier than the other senses. Odors are not easily classified, and primary odors have not really been delineated. Humans can distinguish among about 10,000 odors, but for some reason have a hard time attaching names to odors quite frequently. Figure 4.51: The olfactory system. Odor molecules travel through the nasal passages and stimulate olfactory cilia. An enlargement of these hairlike olfactory receptors is shown in the inset. The olfactory nerves transmit neural impulses through the olfactory bulb to the brain. Figure 4.51 The olfactory system Pheromones In many animals, the sense of smell is used for communication. For example, insects such as ants and termites and vertebrates such as dogs and cats communicate with each other by secreting and detecting odorous signals called pheromones – especially to signal sexual receptivity, danger, territorial boundaries, and food sources. We humans seem to use the sense of smell primarily in conjunction with taste to seek and sample food, but some evidence exists to suggest that people may also use sexual pheromones as well as pheromones that help us identify family members by smell. For more information: Watch this video on PBS called “Sweaty T-Shirts and Human Mate Choice” for an evolutionary perspective on pheromones: http://www.pbs.org/wgbh/evolution/library/01/6/l_016_08.html ABC News article called “Are Pheromones a Secret Weapon for Dating?” http://abcnews.go.com/2020/Health/story?id=1386825 CNN article called “Study Finds Proof that Humans React to Pheromones”: http://www.cnn.com/HEALTH/9803/11/pheromones/index.html Fragrance Effects Research suggests that pleasant scents may trigger pleasant moods and give a boost to workers’ performance. Social psychologist Robert Baron, who has studied these fragrance effects, has patented and is marketing a device that emits pleasant scents. Called PPS (Personal Productivity/Privacy System) it combines fragrance release with a whitenoise generator and an air filter. After testing dozens of smells, Baron found that lemon and light floral had broad appeal (pine was the least popular odor), and is marketing discs producing these odors with the PPS. On a much larger scale, Shimizu Corporation has also patented an “odordelivery” for commercial buildings. For example, it pumps a citrus odor through an office building’s ventilation ducts every two minutes. “The fragrance sense can be fundamental to controlling conditions for office workers,” says Junichi Yagi, a representative for Shimizu. He cites a monthlong study of Japanese keypunchers in which those who inhaled a lemon aroma make 54 percent fewer errors than those who sniffed plain air. While the citrus odor seemed to make people more alert, other smells, such as spiced apple, seemed to aid relaxation. Fragrance Effects (cont.) Researchers are investigating the effects of various fragrances in diverse settings. In some cases, they have reported dramatic success. For example, Susan Schiffman of Duke University has explored how pleasant odors may influence the disposition of New York City subway riders. In pumping scents through one subway car and not another, she reported finding that some food odors cut shoving and pushing by 40 percent. She has also reported success in using an apricot scent to help patients at a weight loss clinic to relax. Many overweight people, she claims, eat compulsively when they’re under stress and the aroma technique has proven beneficial. William Redd and Sharon Manne at Memorial SloanKettering Cancer in New York City used a vanilla scent to lessen patient anxiety. Those who detected the scent and perceived it as pleasant reported a drop in anxiety by as much as 65 percent. Baron and his colleagues also found that shoppers in Crossgates Mall in upstate New York were more likely to help a stranger if they smelled roasting coffee or baking cookies. “There’s nothing magical,” Baron said. “When you put people in a good mood, they become more helpful.” Read about the importance of smell in marketing! http://www.tampabay.com/features/humani nterest/article1203774.ece
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