Taste good? Senses inform the brain — but don’t tell everyone the same thing | Science News for Students

Taste good? Senses inform the brain — but don’t tell everyone the same thing

By mapping how the body determines flavor, scientists reveal clues that could help people eat better
Aug 2, 2018 — 6:45 am EST
a girl with braces enjoying a slice of pizza

All our senses inform what we taste. 

MarianVejcik/iStockphoto

Food Network host Andrew Zimmern once asked Taria Camerino: “What do I taste like?” It’s a strange question. But not for Camerino. This Atlanta-based chef is one of many people who sense their world in special ways.

Camerino was born with synesthesia (Sin-uhs-THEE-zhah). That means her senses are tangled up with one another. (The term comes from the Greek words syn, meaning together, and aesthesis, meaning sensation.)

Some synesthetes see each letter of the alphabet in a particular color. Others see shapes when they hear music. Camerino’s brain links things she sees and hears to flavors. That’s how she could answer Zimmern’s unusual question.

“I watched the way he moved,” she recalls, and discovered that he tasted like toasted prawn shells and bay-leaf syrup. Her unusual sensory ability lets her understand people through food. Sometimes, she uses this gift to aid people. Some illnesses dull their victims’ senses. With Camerino’s help, some who had lost much of their sense of taste regained “more connection to [it].”

Most people are not synesthetes. But everyone’s senses work together to process taste. Scientists are discovering how these connections affect what we eat. They’re also learning how tastes’ hidden meanings might lead to behaviors that might make people sick — or do the opposite: encourage healthier eating.

a woman is blindfolded and tasting something while other people look on
Here, participants at a Kentucky conference on “neurogastronomy,” or the study of taste in the brain, test whether they can taste what they cannot smell.
James K Morris, University of Kentucky

Tastes carry hidden meanings

For the most part, people process different sensations — taste, smell, hearing, touch and sight — in different parts of the brain’s cerebral (Seh-REE-brul) cortex. That’s its outermost layer. But all the senses talk to each other through neural networks. These are groups of interconnected brain cells, called neurons.

The signaling between these sensory cells lets us hear the crispy crunch of a potato chip and know it’s fresh. Or see a plump peach and think, “Yum, that looks sweet!” The information we get from this chatter helps us decide what to eat.

three macarons on a white background
We anticipate taste based on how food looks. Expecting sweet but getting salty turns us off.
Tatiana Lapina/Unsplash (CC0)

What and how we make those decisions interests Julie Mennella. She works at the Monell Chemical Senses Center in Philadelphia, Pa. As a biopsychologist (BY-oh-sy-KOL-oh-gist), she studies how behaviors can be affected by taste preferences that develop during infancy and early childhood.

Early in human history, the ability to recognize and respond to different tastes without thinking helped people survive. A sweet taste, explains Mennella, isn’t just pleasing. It also tells someone that a food is rich in calories. That’s important because calories provide the energy needed to fuel our bodies. A salty taste indicates that food contains salt — sodium chloride. It’s a mineral needed for bone health, especially when bones are growing during childhood.

Sour and bitter tastes also carry messages — negative ones that might cause you to spit a food out. A sour taste told our ancestors a food might be spoiled. A bitter taste might have meant a meal was poisonous.

You might enjoy eating sour fruits such as lemons or grapefruit, or bitter vegetables such as turnips or Brussels sprouts. But you probably learned to like their tastes over time.

Today, most of us don’t have to hunt or forage for food as our ancient ancestors did. We can find plenty of meat and fruit — and chips and cookies — at the supermarket. What scientists call our food environment has changed.

Our brains still give us cues that guide our food choices, though. And that can be a problem — especially for kids. Mennella found in a 2016 study that kids and teens prefer far sweeter tastes than do adults.

This preference can set kids on a lifelong path to unhealthy eating. A sweet tooth can lead to overeating — and obesity. It also ups the risk someone will develop diseases such as diabetes. A strong preference for salty foods can foster overeating, too. It’s also been linked to health problems such as high blood pressure. Such issues have been growing throughout the world’s wealthier nations. By studying taste, Mennella and other scientists are searching for clues about how we sense foods in hopes of learning how to turn those risks around.

Tricking taste

Some people are drawn to really sweet things. Others, not so much. Scientists would like to know whether we’re born with these preferences.

In her own work, Mennella has found that what parents feed their infants can affect a child’s likes and dislikes later in life. One 2011 study by her group showed that infants fed sweetened water grew up preferring sweet drinks. Babies given unsweetened water did not. This suggests, she says, that cutting out sugary drinks might help infants develop into kids without an intense hankering for sweet treats.

Her goal is not to deprive children of all sweet treats. What fun would that be? Instead, she says, “We’re trying to figure out if we can shift their preference for added sugars.” (Added sugars are those that manufacturers — or diners — add to those naturally present in foods.)

Can kids be convinced to choose a banana instead of a cookie, for example? “We want to uncover some of the mysteries of how we can get children to like healthy foods,” says Mennella — such as, how many exposures to a fruit will they need before they actively reach for the fruit.

Danielle Reed is a behavioral geneticist at Monell who works with Mennella. Her lab conducts research on taste, too. But Reed is trying to find out if there is a genetic reason for taste preferences. Are we born liking or disliking super-sweet or salty tastes? For example, she says, do people tend to inherit a strong preference for certain tastes because of their genetics — or just learn to like them?

Reed has been studying identical twins. People who grow up in the same household, eating the same foods, may “learn” to prefer the tastes that their parents have been feeding them. To test whether they instead inherited that preference, she compares siblings. Identical twins share the same genes — and usually the same household, as kids — so one would expect their taste preferences to be similar. But are taste preferences equally similar in fraternal (non-identical) twins and in siblings who aren’t twins?

In one 2015 study, her team confirmed that identical twins indeed prefer similar levels of sweetness most of the time. In contrast, sweet preferences could vary a lot among fraternal twins and non-twins. Reed concludes that some aspects of how foods taste to us are inherited.

And this isn’t true only for sweetness, she notes, but for bitterness as well. Some people may be biologically wired to find turnips too bitter to eat. Others might not find them bitter at all.

Reed says that people born to prefer sweets may have to work harder to avoid overeating them. But kids who find turnips too bitter to eat don’t have to give up on all vegetables. Their parents can simply seek alternatives that taste good to them — maybe carrots or peas.

More than meets the tongue

Dana Small is a clinical psychologist at Yale University in New Haven, Conn. She studies how people’s brains respond to taste and smell, and to the two senses together. People tend to pick up flavor preferences, she says, depending on what food is available where they live or on what was served to them as children.

350_Gastrometer.png
Dana Small and a team in her lab's electronics and machine shop assembled this machine to deliver precise amounts flavored liquids onto the tongue of a subject lying in a brain scanner.
Dana Small and the John B. Pierce Laboratory Electronics and Machine Shop

For example, American children “might find a plate of deep-fried bugs highly repulsive,” she notes. “But if you grew up in Indonesia eating them as a snack, you would have learned to find them delicious.”

Like Mennella and Reed, Small is trying to understand eating behaviors that can lead to obesity and diabetes. Her studies look inside people’s brains to see how tastes and smells affect their flavor perceptions.

Volunteers lie in a type of brain scanner known as an fMRI machine. (The initials stand for functional magnetic resonance imaging.) As they lie there, another machine drops bits of liquid into their mouths. These liquids contain different flavorings. Yet another device delivers specific odors across their noses. The fMRI scanner shows where brain activity spikes in response to those tastes and smells. Those brain sites show how we’re responding to the tastes and smells.  

In one 2015 study, Small’s team studied how being sated — no longer hungry — affects the brain’s response to food cues. The researchers pumped the smells and flavors of a milkshake, then mac and cheese, into the noses and mouths of 32 volunteers. This triggered activity in a brain area called the amygdala (Ah-MIG-duh-lah). It’s a brain area that responds to food cues when people are hungry. Small says this is usually reduced after a meal. Yet, even though all of her volunteers had just eaten, some of them still showed a big response to the food cues. And these people, it turned out, also were the ones most likely to have gained weight over the next year.

Small is not sure yet how this research may one day be used to tackle unhealthy eating patterns. For now, she says, “We are just trying to understand how unhealthy eating works.” Later, researchers might work on changing unhealthy patterns.

The role of foods’ appealing smells

Timothy McClintock also is studying the role of smells in helping to define a food’s flavor. As a physiologist (Fiz-ee-OL-oh-gist) at the University of Kentucky in Lexington, he studies how different parts of the body work. He has been working to “map” cells in the brain that respond to scents.

olfactory receptors
This is an up-close peek at olfactory receptor neurons. The human tongue has about 10 million of these receptors, which help us smell.
Timothy McClintock, University of Kentucky

To do this, he replaces a gene in certain nerve cells of mice. These olfactory (Oal-FAK-tuh-ree) cells respond to scents by emitting light — fluorescing. By looking for that telltale light, he can spot which nerve cell is related to which odor receptor — and therefore, to which smell. So far, McClintock has “mapped” receptors for 10 different smells.

If McClintock can learn which receptors and smells link up, this might help researchers “develop flavors that do a better job of appealing to us,” he says. Using his research, maybe scientists will one day be able to “develop chemicals that block receptors we don’t want to smell.” That could be good news for cancer patients who undergo chemical treatment — chemotherapy — to fight their disease.

“Chemo” can change the way foods smell and taste to these patients. It could, for instance, give a peach a salty taste when someone had been expecting it would be sweet. That distorted sense of taste, he notes, “can really throw you off to the point where you don’t like a food.” It may even prompt some patients to stop eating — even though their bodies need the energy to heal.

Smell also influences taste and flavor, McClintock notes. When you bite down on that peach, its juices release odor molecules. These travel through a passage that runs from your mouth to a large open space, known as the naval cavity, at the back of the nose. Those scented molecules then dissolve into mucus, before meeting up with scent receptors that are attached to sensory nerve cells.

a photo of sausages cooking on a grill
Our sense of smell is critical to our sense of taste.
The Digital Marketing Collaboration/Unsplash (CC0)

Each kind of odor fits into a special slot in receptors found high up in the nasal cavity. When the scent molecules reach a receptor, the nerve cells in the nose fire off electrical signals. These signals travel to the olfactory bulb, which is the brain’s first processing station for odor information. From there, the signal moves on to the brain system that deals with emotions. Other nerves relay that information to the brain’s olfactory cortex, a brain region where more odor processing takes place.

The rest of our senses also are involved in flavor. When you look at a slice of pizza, the optic nerve at the back of your eye transmits a message about it to your brain’s visual cortex. This gives you your first clue about what to expect from its taste, says McClintock. When you put the pizza in your mouth, it’s probably still warm from the oven. That’s temperature, which is a part of touch. It’s important to flavor, as well, says McClintock. Compare your warm pizza to a cold leftover slice. The warm one has more flavor — in part because taste receptors are sending stronger messages to our brains.  

Taste to the rescue

Recently, Camerino, the synesthetic chef, helped tackle some of McClintock’s concerns about the health of chemo patients. At a conference at the University of Kentucky, chefs and scientists like McClintock discussed how taste plays out in our brains.

Later, Camerino made a dessert that she hoped would taste good to cancer patients on chemotherapy. The dish was a cake made with oranges and topped with a sauce made of ground-up basil and pistachios. Camerino thought the citrus flavor of the oranges would cut through the metallic taste that she knew some chemo patients experience. And she thought they might be able to somehow “feel” the basil on the tops of their mouths, even if they couldn’t taste it.

The result was promising: The cancer patients rated her creation “delightful and unexpected!”

a photo of Taria Camerino preparing a dessert
Chef Taria Camerino puts the finishing touches on a clementine upside-down cake with basil-pistachio pesto and crème fraiche gelato.
James K Morris, University of Kentucky  

Power Words

(for more about Power Words, click here)

amygdala     An area deep within the brain and near the temporal lobe. Among other things, the amygdala plays a role in emotions. The term comes from the Greek word for an almond, which this region resembles in shape.

behavior     The way something, often a person or other organism, acts towards others, or conducts itself.

blood pressure     The force exerted against vessel walls by blood moving through the body. Usually this pressure refers to blood moving specifically through the body’s arteries. That pressure allows blood to circulate to our heads and keeps the fluid moving so that it can deliver oxygen to all tissues. Blood pressure can vary based on physical activity and the body’s position. High blood pressure can put someone at risk for heart attacks or stroke. Low blood pressure may leave people dizzy, or faint, as the pressure becomes too low to supply enough blood to the brain.

bug     The slang term for an insect. Sometimes it’s even used to refer to a germ.

calorie     The amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. It is typically used as a measurement of the energy contained in some defined amount of food.

cancer     Any of more than 100 different diseases, each characterized by the rapid, uncontrolled growth of abnormal cells. The development and growth of cancers, also known as malignancies, can lead to tumors, pain and death.

cavity     (in geology or physics) A large rigid pocketlike structure. (in biology) An open region pocketlike structure surrounded by tissues. Or (in dentistry) a tiny hole in a tooth that develops over time. Dental cavities are more likely to happen when a person eats a lot of sugar or does not brush and floss regularly. Dentists refer to these as caries.

cell     The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall.

cerebral cortex     (pl. cerebral cortices) The outermost layer of neural tissue covering the front part of a vertebrate animal’s brain.

chemical     A substance formed from two or more atoms that unite (bond) in a fixed proportion and structure. For example, water is a chemical made when two hydrogen atoms bond to one oxygen atom. Its chemical formula is H2O. Chemical also can be an adjective to describe properties of materials that are the result of various reactions between different compounds.

chemotherapy     A chemical treatment that’s most often used to kill cancer cells in the body. Chemotherapy can have many unpleasant side effects as it kills not only cancer cells but many healthy cells as well.

citrus     A genus of flowering trees that tend to produce fruits with a juicy edible flesh. There are several main categories: the oranges, mandarins, pummelos, grapefruits, lemons, citrons and limes.

cortex     The outermost layer of neural tissue of the brain.

diabetes     A disease where the body either makes too little of the hormone insulin (known as type 1 disease) or ignores the presence of too much insulin when it is present (known as type 2 diabetes).

diet     The foods and liquids ingested by an animal to provide the nutrition it needs to grow and maintain health. (verb) To adopt a specific food-intake plan for the purpose of controlling body weight.

dissolve     To turn a solid into a liquid and disperse it into that starting liquid. (For instance, sugar or salt crystals, which are solids, will dissolve into water. Now the crystals are gone and the solution is a fully dispersed mix of the liquid form of the sugar or salt in water.)

environment     The sum of all of the things that exist around some organism or the process and the condition those things create. Environment may refer to the weather and ecosystem in which some animal lives, or, perhaps, the temperature and humidity (or even the placement of components in some electronics system or product).

flavor     The particular mix of sensations that help people recognize something that has passed through the mouth. This is based largely on how a food or drink is sensed by cells in the mouth. It also can be influenced, to some extent, by its smell, look or texture.

fluorescent     (v. fluoresce) Adjective for something that is capable of absorbing and reemitting light. That reemitted light is known as fluorescence.

food environment     A term used for types and the availability of foods to which people have access. For instance, people in low-income, urban areas may not have ready access to free produce much of the year. People in rural areas may have limited access to seafood or exotic foods.

forage     To search for something, especially food. It’s also a term for the food eaten by grazing animals, such as cattle and horses.

fraternal    (in genetics) The term for a type of twin birth where each baby comes from a separate fertilized egg. This is in contrast to identical twins, which result from a single fertilized egg (creating two separate but nearly identical babies).

functional magnetic resonance imaging (fMRI)    A special type of medical scanning technology for studying brain activity. It uses a strong magnetic field to monitor blood flow in the brain as an individual is performing some task (from reading or viewing pictures to thinking about various spoken words). Tracking areas of elevated blood flow can tell researchers which brain regions are especially active during those activities.

gene     (adj. genetic) A segment of DNA that codes, or holds instructions, for a cell’s production of a protein. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves.

genetic     Having to do with chromosomes, DNA and the genes contained within DNA. The field of science dealing with these biological instructions is known as genetics. People who work in this field are geneticists.

high blood pressure     The common term for a medical condition known as hypertension. It puts a strain on blood vessels and the heart.

mineral     Crystal-forming substances that make up rock, such as quartz, apatite or various carbonates. Most rocks contain several different minerals mish-mashed together. A mineral usually is solid and stable at room temperatures and has a specific formula, or recipe (with atoms occurring in certain proportions) and a specific crystalline structure (meaning that its atoms are organized in regular three-dimensional patterns). (in physiology) The same chemicals that are needed by the body to make and feed tissues to maintain health.

molecule     An electrically neutral group of atoms that represents the smallest possible amount of a chemical compound. Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms (O2), but water is made of two hydrogen atoms and one oxygen atom (H2O).

mucus     A slimy substance produced in the lungs, nose, digestive system and other parts of the body to protect against infection. Mucus is made mainly of water but also includes salt and proteins such as mucins. Some animals use mucus for other purposes, such as to move across the ground or to defend themselves against predators.

nasal     Having to do with the nose.

nasal cavity     The big open space inside the nose. It sits between the bottom of the skull and roof of the mouth. A mucus membrane lines its walls. This region helps to warm and filter the air we breathe in. And sensory cells within it also can pick up scents and relay that information to the brain.

nerve     A long, delicate fiber that transmits signals across the body of an animal. An animal’s backbone contains many nerves, some of which control the movement of its legs or fins, and some of which convey sensations such as hot, cold or pain.

network     A group of interconnected people or things. (v.) The act of connecting with other people who work in a given area or do similar thing (such as artists, business leaders or medical-support groups), often by going to gatherings where such people would be expected, and then chatting them up. (n. networking)

neural network     A computer program designed to work in a way similar to the human brain. The programs can “learn” from examples, just as the brain does.

neuron     An impulse-conducting cell. Such cells are found in the brain, spinal column and nervous system.

neuroscience     The field of science that deals with the structure or function of the brain and other parts of the nervous system. Researchers in this field are known as neuroscientists.

obesity     (adj. obese) Extreme overweight. Obesity is associated with a wide range of health problems, including type 2 diabetes and high blood pressure.

olfaction     (adj. olfactory) The sense of smell.

olfactory bulb     A region in the front of the brain that receives information from smell-receptor nerves in the nose (and nasal cavity).

optic nerve     A nerve that carries information, as electrical impulses, to the brain from the retina of the eye. The brain then translates those signals to images.

perception     The state of being aware of something — or the process of becoming aware of something — through use of the senses.

physiologist     A scientist who studies the branch of biology that deals with how the bodies of healthy organisms function under normal circumstances.

prawn     A large marine crustacean that resembles a shrimp. The term is also applied to some large species of shrimp.

pressure     Force applied uniformly over a surface, measured as force per unit of area.

receptor     (in biology) A molecule in cells that serves as a docking station for another molecule. That second molecule can turn on some special activity by the cell.

risk     The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)

salt     A compound made by combining an acid with a base (in a reaction that also creates water). The ocean contains many different salts — collectively called “sea salt.” Common table salt is a made of sodium and chlorine (sodium chloride).

scanner     A machine that runs some sort of light (which includes anything from X-rays to infrared energy) over a person or object to get a succession of images. When a computer brings these images together, they can provide a motion picture of something or can offer a three-dimensional view through the target. Such systems are often used to see inside the human body or solid objects without breaching their surface.

sibling     An offspring that shares the same parents (with its brother or sister).

sodium     A soft, silvery metallic element that will interact explosively when added to water. It is also a basic building block of table salt (a molecule of which consists of one atom of sodium and one atom of chlorine: NaCl). It is also found in sea salt.

synesthesia     A brain condition in which a person connects a sensory experience to an unassociated symbol, as a letter or number. People who have this trait are known as synesthetes.

taste     One of the basic properties the body uses to sense its environment, especially foods, using receptors (taste buds) on the tongue (and some other organs).

transmit     (n. transmission) To send or pass along.

visual cortex      A part of the cerebral cortex (the outermost nerve tissue covering the front part of the brain) that receives visual information from the eye that will be transformed into images.

Citation

Journal: J. A. Mennella and N.K. Bobowski. Psychophysical tracking method to measure taste preferences in children and adults. Journal of Visualized Experiments, Issue 113, July 2016, p. e54163. doi: 10.3791/54163.

Journal: P.V. Joseph et al. Individual differences among children in sucrose detection thresholds relationship with age, gender and bitter taste genotype. Nursing Research. Vol. 65, January 2016, p. 3. doi: 10.1097/NNR.0000000000000138.

Journal: L. Huang et al. A common genetic influence on human intensity ratings of sugar and high-potency sweeteners. Twin Research and Human Genetics. Vol. 18, August  2015, p. 361. doi: 10.1017/thg.2015.42.

Journal: X. Sun et al. Basolateral amygdala response to food cues in the absence of hunger is associated with weight gain susceptibility. The Journal of Neuroscience. Vol. 35, May 20, 2015, p. 7964. doi:10.1523/jneurosci.3884-14.2015.

Journal: T. McClintock et al. In Vivo identification of eugenol-responsive and muscone- responsive mouse odorant receptors. The Journal of Neuroscience. Vol. 34, November 19, 2014, p. 15669. doi:10.1523/jneurosci.3625-14.2014.

Journal: A. K. Ventura and J. A. Mennella. Innate and learned preferences for sweet taste during childhood. Current Opinion in Clinical Nutrition and Metabolic Care. Vol. 14, July 2011, p. 379. doi: 10.1097/MCO.0b013e328346df65.

Further Reading