The enzymes in snot may help to change the chemical makeup of odors that enter the nose. Credit: ptaxa/iStock

Snot is often what shows up after a hard sneeze. It’s a constant companion of allergies and the common cold. It’s wet, sticky and — to most people — best left up the nose.

But snot, or mucus, also contains many different kinds of proteins. Those proteins may play an important role in something else that happens in the nose: smelling. In a recent study, researchers from Japan’s University of Tokyo showed that proteins in mucus change the makeup of odors before those scents even make it to smell receptors. Smell receptors are also proteins. They stick out from the cells that send signals about a smell to the brain, which identifies the odor.

That means that sticky, wet, gross mucus might have a more glamorous role: It may be important for smelling smells.

It seems natural to assume a connection between smells and snot. After all, the human nose is home to the sense of smell — and is an exit for snot. But “most people and most scientists pay no attention at all to mucus,” neuroscientist Leslie Vosshall told Science News. Vosshall is at Rockefeller University in New York City and was not involved in the recent study.

Scientists suspect that some molecules in mucus carry smells to other parts of the nose, where they can be detected. Other molecules in snot are enzymes, which start chemical reactions. Some enzymes may protect the body by chopping toxic substances — such as inhaled chemicals — into smaller, safer chunks. But until now, scientists did not know whether this chopping action could affect the smell of something.

To learn about smells and mucus, the researchers experimented on mice. They removed mucus from the noses of mice. Then, they mixed in chemicals that have particular odors. One of these chemicals was benzaldehyde, also known as artificial almond oil. After five minutes in mouse snot, the benzaldehyde had broken down into two chemicals — one that had no smell and another that did.

When the researchers inactivated the enzymes, by boiling the mucus, and then tried the same experiment again, the benzaldehyde did not break down.

That part of the experiment showed that the mucus could change the chemical composition of odors. Next, the researchers showed that the mice brains also register this difference. For this part of the project, the scientists “turned off” the mucus chemicals in the mice noses that usually chop up odorous molecules. As a result of this change, the mouse brains reacted differently than they did before — showing that their brains had picked up on the change.

The researchers also used mouse behavior to show that mucus changes the smell of something. For this part of the experiment, they used mice that had been trained to identify certain smells. (In training, the mice had been given treats when they went to those smells. After training, the mice naturally went back to those smells, hoping for more treats.) When the scientists turned off the important molecules in the mouse mucus, the mice were unable to recognize those favorite smells.

Scientists don’t know whether the molecules in mucus work the same way in people. Human mucus does have many of the same proteins as the mucus in mouse noses, so it’s worth investigating. Early studies do suggest that human snot can change odors, so stay tuned. And cover your nose when you sneeze.

POWER WORDS (adapted from the Yahoo! Kids Dictionary)

olfactory Of, relating to, or contributing to the sense of smell.

proteins Fundamental components of all living cells, including many substances, such as enzymes, hormones and antibodies, that are necessary for the proper functioning of an organism.

molecule A group of like or of different atoms held together by chemical forces.

enzyme Any of numerous proteins produced by living organisms that function as biochemical catalysts.

bacteria Single-celled microorganisms that vary in terms of morphology, oxygen and nutritional requirements, and motility. They may be free-living, saprophytic, or pathogenic in plants or animals.

In a new study of visual abilities, researchers asked volunteers to identify the biggest orange circle. Here, each orange circle on the right is a little bit larger than the one on the left. Misleading images usually fooled adults but not children, while

Can you believe your eyes? A recent experiment suggests that the answer to that question may depend on your age.

In the experiment, kids and adults were asked to look at the same visual illusion — a picture that was designed to trick the viewer. The researchers who ran the experiment say that adults were more easily fooled by the illusion, and that the kids, especially those younger than age 7, saw the picture more accurately.

Martin Doherty, a psychologist at the University of Stirling in Scotland, led the team of scientists. A psychologist is a scientist who studies behavior and processes in the brain and may offer counseling to patients. Doherty says that his experiment can tell scientists something about how the human brain develops. In particular, the experiment shows that what the brain does to “see” visual context is a process that develops slowly.

The words “visual context” refer to how a person sees something in relation to the things around it. A baseball may look large when next to a golf ball, for example, but appear small when next to a basketball.

In this experiment, Doherty and his team tested the perception of the participants using pictures of solid orange circles. The researchers showed the same pictures to two groups of people. The first group included 151 children ages 4 to 10, and the second group included 24 adults of ages 18 to 25.

The first group of pictures showed two circles alone on a white background. One of the circles was larger than the other, and the participants were asked to identify the larger one. Four-year-olds identified the correct circle 79 percent of the time. Adults identified the correct circle 95 percent of the time.

Next, both groups were shown a picture where the orange circles, again of different sizes, were surrounded by gray circles. Here’s where the illusion came in — remember the baseballs, golf balls and basketballs.

If an orange circle is surrounded by smaller gray circles, then it appears larger than it really is. If an orange circle is surrounded by larger gray circles, then it appears smaller than it really is.

But the experiments added a twist: In some of the pictures, the smaller orange circle was surrounded by even smaller gray circles — making the orange circle appear larger than the other orange circle, which was the real larger one. And the larger orange circle was surrounded by even bigger gray circles — so it appeared to be smaller than the real smaller orange circle.

When young children ages 4 to 6 looked at these tricky pictures, they weren’t fooled — they were still able to find the bigger circle with roughly the same accuracy as before. Older children and adults, on the other hand, did not do as well. Older children often identified the smaller circle as the larger one, and adults got it wrong most of the time.

“When visual context is misleading, adults literally see the world less accurately than they did as children,” Doherty told Science News.

As children get older, Doherty said, their brains may develop the ability to perceive visual context. In other words, they will begin to process the whole picture at once: the tricky gray circles, as well as the orange circle in the middle. As a result, they’re more likely to fall for this kind of visual trick.

Doherty is not the first scientist to study visual context in children, and earlier studies have found that children, just like adults, can be fooled by illusion. Carl Granrud is a psychologist at the University of Northern Colorado in Greeley. He told Science News that Doherty’s findings seem sound, but that they were “somewhat surprising.” He pointed out that in other visual illusion tests, children were fooled, suggesting they had developed the ability to see visual context.

This experiment shows that sometimes, in order to get a sneak peek inside the brain, you have to try to trick it — and see what happens.

POWER WORDS (from the Yahoo! Kids Dictionary)

psychology The science that deals with mental processes and with behavior

optical illusion An image seen with the eyes that is deceptive or misleading.

perceive To become aware of directly through any of the senses, especially through sight or hearing.

context The part of an image that surrounds a particular part of the image and determines its meaning.

Going Deeper:

Studies with mice have shown how the same cells on the tongue that taste sourness also detect fizzy flavors.

What does fizz taste like? In bubbly beverages like soda or champagne, tiny bubbles give the drink a lift — and have a distinct taste. Scientists have long wondered how we taste these bubbles. In a new study on mice, scientists have connected that fizzy-taste sensation to the ability to taste sourness.

Scientists previously thought the taste of bubbles comes from the bubbles bursting on the tongue — but that idea may have to change, says Charles Zuker. A neuroscientist, or a scientist who studies the brain and nervous system, Zuker is now at Columbia University in New York. He and his team of researchers studied the nervous systems of mice to understand how the tongue tastes carbon dioxide, which is the gas that makes up the bubbles.

In the experiment, five different groups of mice were genetically engineered to be missing one taste sensation. (“Genetically engineered” means the researchers were able to turn off the switches for certain tastes by altering the responsible genes.) The mice in one group were bred so that they could not taste sweet. In another group, the mice could not taste sour. In the other three groups, the mice could not taste umami, or salty or bitter.

When the scientists gave carbon dioxide gas to the mice, the nervous systems of the rodents in four groups responded to carbon dioxide. But for mice that could not taste sour, their nervous systems did not show any sign of tasting carbon dioxide.

This tipped off the researchers to the connection between sourness and bubbles. When the scientists turned off the sour taste in the mice genes, they also turned off the ability to taste carbon dioxide.

The scientists then zoomed in on the sour taste. Animals like mice or human beings are able to detect different tastes by using taste buds, located near the surface of the tongue. A taste bud is a group of 50 to 150 cells called taste receptors. (Under a microscope, this bundle of cells looks a little like a big bunch of bananas.) The tips of the taste receptor cells pick up tastes in the mouth, and then send that information to the brain.

When they studied the cells that detect sourness, Zuker and his colleagues found a protein, attached to the sour-sensing cells, that is crucial to the process of tasting carbon dioxide. When carbon dioxide comes into contact with this protein, the protein knocks off particles called protons. These protons, in turn, stimulate the sour cells.

So when a mouse — or person — drinks a fizzy drink, there’s a one-two punch. First, the protein knocks off protons. Second, the protons stimulate the sour-sensing cells —and the brain says, “Hey! That’s a taste!”

That may seem like a lot of work to get from a can of soda to a taste — but the science of the senses is anything but simple. Taste “is a very challenging system to study,” Alexander Bachmanov, a scientist at the Monell Chemical Senses Center in Philadelphia, told Science News. “Everything is very small but very complex.”

POWER WORDS (adapted from the Yahoo! Kids Dictionary)

nervous system The system of cells, tissues and organs that regulates the body’s responses to internal and external stimuli. In vertebrates it consists of the brain, spinal cord, nerves, ganglia and parts of the receptor and effector organs.

neuroscience Any of the sciences, such as neuroanatomy and neurobiology, that deal with the nervous system.

proteins Molecules that contain carbon, hydrogen, oxygen, nitrogen and usually sulfur. Proteins are fundamental components of all living cells and include many substances that are necessary for the proper functioning of an organism.

carbon dioxide A colorless, odorless, incombustible gas formed during respiration, combustion and organic decomposition and used in food refrigeration, carbonated beverages, inert atmospheres, fire extinguishers and aerosols.

Going Deeper:

Some people with synesthesia always see the letters in the alphabet as a certain color. The color of each letter is always the same.

The number “6” is a bright shade of pink. Listening to a cello smells like chocolate. And eating a slice of pizza creates a tickling sensation on the back of your neck.

If you have experiences like this, you may be one of the special people with an unusual sensory condition called synesthesia (pronounced sin-uhs-THEE-zha).

People with synesthesia experience a “blending” of their senses when they see, smell, taste, touch or hear. Such people have specially wired brains, so that when something stimulates one of the five senses, another sense also responds. This blending can cause people to see sound, smell colors or taste shapes.

Dozens of different sensory combinations exist. In the most common form of synesthesia, numbers, letters or even days of the week appear in their own distinct color.

If you’ve encountered these types of events, you’re not alone. Scientists say as many as one in every 200 people may be a synesthetes, as people with this condition are called. The phenomenon is known to run in families, and may occur more often among women than men. Many famous people have had synesthesia, including Russian writer Vladimir Nabokov and physicist Richard Feynman.

One thing is certain; most synesthetes treasure their unusual ability to take in the world with an additional sense. After all, who wouldn’t want to experience the world in full, glorious color or sound?

“It’s absolutely a positive experience,” says Patricia Lynn Duffy, a synesthete who has talked to hundreds of others with the condition while writing a book on the subject. “If you proposed to take away someone’s synesthetic ability, I think they would say, ‘No, I like it this way.’’’

When people with certain types of synesthesia look at the image on the left, they can easily detect the six figures facing the opposite way, as shown in the image on the right. To these people, the “S” figures appear in a different color than the “2″ figu

What Color is my “i”?

Most synesthetes learn about their amazing gift by accident. They are surprised to learn that everyone does not experience the world as they do.

Though it may sound strange to many people, Duffy says the experiences are not scary. The people who have synesthesia have always experienced life that way.

“For as long as I could remember, each letter of the alphabet had a different and distinct color. This is just part of the way alphabet letters look to me,” says Duffy. “Until I was 16, I took it for granted that everyone shared those perceptions with me.”

Synesthetes do not actively think about their perceptions — they just happen. Some synesthetes report that they see such colors internally, in “the mind’s eye.” Others, such as Duffy, see their visions projected in front of them, like watching an image on a movie screen.

Scientists know that in synesthesia, those colors are real, not just figments of an active imagination. How? Studies show that the colors synesthetes see are highly specific and consistent over time. If the letter “b” is lime green, it will always be lime green.

Studies done in the mid-1990s showed that synesthesia also can be measured by brain-scanning techniques. For synesthetes who perceive colors when hearing words, a certain part of the brain involved with vision is active in response to sound. That type of activity didn’t occur in non-synesthetes.

Making Connections

So how can the sound of a musical instrument lead to color?

Scientists are still trying to discover exactly how information from the senses merge together in the brain. But this much is known:

Messages gathered from the eyes, ears, mouth, nose and nerves involved in the sense of touch travel to the brain for processing. Much of this sensory processing occurs in an area of the brain called the cortex, the outermost part of the brain that organizes and enables us to respond to the incoming messages.

Information from each of senses is first processed in its own special region. It’s then sent on to “higher” regions in the cortex for further processing. At certain points in the brain, these various senses converge.

One theory is that synesthesia may be caused by “cross-wiring” between areas of the brain that process different sensations, such as color, sound or taste. This theory draws on the fact that children are born with many nerve connections between nearby parts of the brain.

“During our first few years of life, our brain makes more connections than it needs, and then eventually prunes some of those away,” says Edward Hubbard, a post-doctoral researcher at the French National Institute for Health and Medical Research who studies what causes synesthesia.

One thing that may happen in synesthesia, Hubbard says, is that some of these connections don’t get pruned away. If so, then people may see specific colors with particular letters because they have extra connections between the brain areas involved in word and color perception.

Last summer, a group of scientists in the Netherlands found direct evidence of these types of extra connections.

The researchers used a method called DTI to scan the brains of 18 people with synesthesia. They also looked at the brains of 18 non-synesthetes.

Using a kind of magnetic resonance imaging called DTI (an example is shown above) to look at the brains of synesthetes and non-synesthetes, scientists showed that synesthetes who see colored letters have higher levels of white matter in three different br

DTI (which stands for diffusion tensor imaging) measures how water flows in the brain. Within certain brain tissues, or nerve fibers, water flows more freely in one direction than the other. This is especially true in a type of nerve fiber, or axon, that carries messages from brain cell to brain cell. Commonly called “white matter,” these axons connect different parts of the brain to each other.

By measuring the water flow through these tissues, the scientists could measure how many of these axons there were in each brain region. Brain regions that are highly connected will have more white-matter axons.

In synesthetes who saw colored letters, the scientists found higher levels of white matter in three different brain regions. One was in the letter and word region of the brain, known as V4. The other highly connected areas were found in brain regions involved in consciousness — the awareness that you’re thinking, feeling, seeing, hearing or any number of other things your brain enables you to do.

“We have lots of things impinging upon our senses, and some of them become conscious and some of them don’t,” says Hubbard. “Activity in this area might make a person more consciously aware of a synesthetic experience.”

These findings don’t rule out other possible causes of synesthesia, says Hubbard. Still, he is now working to see if this type of “cross-wiring” occurs in other forms of synesthesia. Other scientists are looking to see whether other parts of the brain are also involved in synesthesia.

Hubbard is also developing better ways to identify the various processing regions of the brain. “Everybody’s brain differs a little bit in its exact organization,” he says.

Duffy notes that these variations in nerve connections occur not only in synesthetes, but in all people.

“Everybody develops a neural pattern that’s kind of unique, just like a fingerprint,” she says. “That’s why no two people are seeing the world in exactly the same way.”

Going Deeper:

Your nose is a living sensor that responds to the chemicals in pizza that give this food its distinctive aroma. Your brain recognizes this combination of odors almost instantly.

Dogs have a much better sense of smell than people do. To make it easier for people to detect and identify odors, chemists have invented electronic noses.

NASA

How does your brain do it? It processes the mixture of chemicals that make up a smell as a pattern and then matches that pattern to one that you’ve already stored in your brain. The particular mix of compounds that gives fresh bread, tomato, garlic, and cheese their aroma, for example, means pizza.

But compared with dogs, people aren’t very good at identifying smells. So, chemists are designing sensors—electronic noses—that help people do this job better.

Electronic noses can go where human noses shouldn’t. For example, some electronic noses can sense substances that would be harmful to humans. Other electronic noses can sense chemicals that people can’t detect at all. Researchers have even built an electronic nose to send into space.

Color patterns

Scientists have been designing and building electronic noses for more than 20 years.

An electronic nose developed by NASA researchers can detect hazardous gases in the air on spacecraft.

NASA

One such device looks a bit like a computer chip covered with neat rows of dots. Each dot contains a chemical dye.

“We use anywhere from 20 to 36 different dyes that change color depending on what chemical they’re exposed to,” says Ken Suslick. He’s a chemist at the University of Illinois at Urbana-Champaign.

Some of the dyes are made of materials that change color to show how acidic or basic a chemical is. If you’ve ever used litmus paper, you know how this works. This paper contains a dye that turns red for an acid, such as lemon juice, or blue for a base, such as baking soda.

To use their nose-on-a-chip, Suslick and his coworkers expose it to chemicals that they’re interested in. The chips can detect chemicals in liquids as well as in solids. A scanner detects any color changes that occur after exposure.

The resulting color pattern is like a chemical fingerprint. Each pattern is unique to a single odor or mixture of odors, Suslick says.

Connecting the dots

To find out what the colored dots mean, chemists need a reference library that contains the patterns created by compounds responsible for the smells of different substances.

Each spice and herb has a distinctive smell and produces its own fingerprint of colored dots.

ChemSensing

Your brain already holds such a library. You collect smells all your life, and whenever you sense an odor, your brain tries to connect it with one that’s already familiar to you.

“So, if you smell something, you can almost hear the gears in your brain clicking, saying, ‘Gee, what does that smell like?’” Suslick says. “And you’re sort of going through a list in your head. That’s the library.”

When your brain makes a match, it identifies the smell.

To build a library for his electronic nose, Suslick has exposed the chip to many substances and recorded the resulting patterns of colored dots. With such a collection of patterns in his library, he can then compare the colors produced by a known substance with what he sees for an unknown material.

Ken Suslick’s nose-on-chip can detect different brands and types of soda.

ChemSensing

Chemicals in space

Electronic noses can also alert people to hazards. On the space shuttle or in the International Space Station, for example, a chemical leak could mean a problem with the spacecraft or danger for the crew. Detecting such leaks promptly is essential.

So, NASA researchers are working on the design and testing of an electronic nose, which they call the ENose. They hope that ENose will one day monitor the inside of a spacecraft to make sure that there aren’t any chemical leaks, says Amy Ryan. She’s a chemist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

Amy Ryan holds an early version of ENose.

NASA

ENose uses a set of four chips, each of which has eight sensors. Each sensor consists of a thin plastic film that expands or contracts, depending on the compounds in the air. The reactions of the individual films create a pattern. Like the human brain, the ENose is programmed to recognize these patterns and smells.

Once it’s in place on a spacecraft, ENose will run 24 hours a day, 7 days a week, monitoring the air to make sure that dangerous substances, such as mercury, or coolants, such as Freon, aren’t present in the cabin.

NASA tested an early version of the device for 6 days on a space shuttle mission in 1998, Ryan says. Now, they’re gearing up for a 6-month test on the International Space Station, planned for 2008.

Although the sensors are finished, Ryan is still working on the chemical library and the software that will keep the ENose running in space. She won’t be on the space station with the ENose, so the ENose will send information from the space station to her computer in California.

But even this sensitive space sensor can’t compete with a dog’s amazing ability to detect and identify smells. Electronic noses still have a long way to go to top a dog’s sniffer.

Going Deeper:

Additional Information

Questions about the Article

Word Find: Electronic Nose

Sounds are a big part of life for people who can hear. But you probably don’t spend much time thinking about what goes on inside your ears—or about how loud sounds might affect your hearing.

The roar of crashing waves is among the many natural sounds that we can experience.

A recent survey on MTV’s Web site found that a mere 8 percent of young people say that hearing loss is “a very big problem.” In comparison, 45 percent of respondents thought that smoking is a major health problem, 31 percent ranked nutrition and weight issues as a priority, and 18 percent put acne near the top of the list.

While these issues are indeed important, it would do kids and teenagers a lot of good to care more about their ears, say the researchers who designed the survey. They work at the Massachusetts Eye and Ear Infirmary (MEEI), Harvard Medical School, and the Harvard School of Public Health.

One large study by scientists at the Centers for Disease Control and Prevention (CDC) found that nearly 13 percent of young people, ages 6 to 19, have some hearing loss caused by exposure to loud noise. That’s more than 5 million kids in the United States who no longer hear as well as they once did.

Most of the time, hearing loss in young people is mild or temporary, but it can be a warning sign of more serious hearing problems to come.

Noise machines

Ears, when they work well, are nifty and intricate little machines.

Sound enters the outer ear canal as a wave. The sound wave travels down the canal to the eardrum, causing it to vibrate. The eardrum, in turn, excites three little bones, which vibrate and amplify the sound. The small bones pass the sound on to the inner ear and a structure called the cochlea. The cochlea is shaped like a snail shell and filled with liquid.

Sound waves travel down the ear canal and cause the eardrum to vibrate. The eardrum, in turn, excites three small bones (hammer, anvil, and stirrup), which amplify the sound and send it to the cochlea.

NASA

Inside the cochlea are delicate structures called hair cells, which are responsible for sending electrical signals to the brain. They let the brain know that the ears have heard something. Hair cells are essential for hearing, but loud noises damage them. And, unlike cells in the skin and other parts of the body, hair cells don’t grow back.

Some researchers are trying to find ways to grow new hair cells in the lab or help the body grow its own.

Loud music

Severe hearing loss occurs most often in elderly people. But the damage happens gradually, and it often begins in childhood.

The goal of the new survey was to find out how likely kids are to experience ear damage, how much they know about hearing loss, and how willing they might be to change their habits.

Listening regularly to loud music can affect a person’s hearing.

The researchers used the Internet to distribute their 28-question survey because they wanted to reach a lot of young people. They used MTV’s Web site, in particular, because they guessed that people visiting this site listened to lots of music, much of it loud. In just 3 days, the scientists collected the opinions of nearly 10,000 visitors.

“This is the first study that has ever been done concerning awareness of hearing loss by kids on such a large scale,” says MEEI physician Jeannie Chung.

One surprising outcome was that 61 percent of young people who answered the survey said that they had felt ringing in their ears or had trouble hearing after a concert. These sensations by themselves usually last for just a short time before hearing returns to normal. After repeated exposure to loud music and other intense sounds, however, temporary hearing loss can become permanent.

Earplugs

One of the best ways to keep a strong sense of hearing into old age, experts say, is to keep a pair of earplugs in your pocket.

A loud vacuum cleaner might be a good reason to wear earplugs while doing household chores.

E. Sohn

If you end up stuck in a traffic jam beside a jackhammer, or standing next to the speakers at a rock concert, pop them in. Earplugs don’t change the quality of sounds, Chung says. They only dampen the noise.

“It’s like sunscreen,” she says. “One sunburn is not going to give you cancer, but multiple sunburns will.”

Noise, likewise, is okay, as long as you don’t overdo it. “We’re not saying you shouldn’t go to rock concerts or clubs or listen to loud music,” Chung says. “We’re saying that you should be aware of it. Do things to protect yourself while you’re having fun.”

One result from the MTV survey was particularly encouraging to the researchers. While only 14 percent of the young respondents said they had used earplugs to protect their ears, a full 66 percent said they would be more likely to use them if they had known about the possibility of suffering hearing loss. Fifty-nine percent said they would be more likely to use earplugs if their doctors talked to them about it.

So, now you know. You needn’t be afraid of going deaf someday. Just take care of your ears, and they’ll give you something to dance about for a long time to come.

Going Deeper:

Scientist’s Notebook

Additional Information

Questions about the Article

Word Find: Hearing