Tag Archives: smell

The eastern mole (Scalopus aquaticus) has its nostrils very closely separated, however it's been proven to be the first mammal to posses stereo smell. (c) Kenneth Catania, Wikipedia Commons

Moles smell in stereo to navigate for food

The eastern mole (Scalopus aquaticus) has its nostrils very closely separated, however it's been proven to be the first mammal to posses stereo smell. (c) Kenneth Catania, Wikipedia Commons

The eastern mole (Scalopus aquaticus) has its nostrils very closely separated, however it’s been proven to be the first mammal to posses stereo smell. (c) Kenneth Catania, Wikipedia Commons

Stereo sensing is a highly important skill that most animals possess that creates a directional perspective. Not all senses are stereo, however, in some animals. For instance, humans have stereo vision and hearing, however no stereo smell – the latter being a trait that not too many animals possess. The common mole has been found to display such an ability, after researchers at Vanderbilt University found the mammal relies on stereo smell to locate prey.

Few animals have so far been proven to have stereo smell, like some species of ants and sharks, although some that heavily rely on their sense of smell like pigs, mice or dogs might also possess this skill. The common mole (Scalopus aquaticus), which can be found wrecking havoc through backyard gardens anywhere from eastern United States and Canada to Mexico, is now the first mammal proven to smell in stereo.

“I came at this as a skeptic,” neuroscientist Kenneth Catania of Vanderbilt University was quoted as saying in a press release. “I thought the moles’ nostrils were too close together to effectively detect odor gradients. The fact that moles use stereo odor cues to locate food suggests other mammals that rely heavily on their sense of smell, like dogs and pigs, might also have this ability.”

The human auditory system is able to discriminate whether a sound comes from the right or from the left, if it is located behind, in front of, below or above the hearer. As a matter of fact, humans can distinguish sounds from two different sources, where the angle between the sources is only 3° – that’s very accurate. Similarly, with stereo smell one can detect different odor sources from each sources, with the brain being also wired to detect these differences. A sense of depth and orientation all based on smell is thus possible – for the common mole, at least.

Catania’s inspiration to study the common mole can be tracked back as far as ten years ago when he studied another mole, the star-nosed mole which uses a sort of tentacle-like tissue on its nose to sense food by touch.  He decided to test the common moles’ capability to find prey for comparison purposes.

“I expected the common mole, which is virtually blind and doesn’t have a very good sense of touch, to be a lot worse than the star-nosed mole. So I was quite surprised when they turned out to be very good at locating prey. At the time, I figured that they must be using their sense of smell, but I didn’t pursue the matter.”

[Also read] White smell: the neutral fragrance discovered by scientists

Since the two performed the same at finding food, despite sensing discrepancies between the two species, Catania naturally reasoned that the common mole’s sense of smell must be more sophisticated that previously thought. Catania presumed the mole must have stereo smell in order to guide itself and find mole, considering all its other senses didn’t provide navigation, so he put his idea to the test.

Where’s that smell coming from?

sniffHe made a radial arena with food wells spaced around a 180-degree circle with the entrance for the mole located at the center. Multiple tests were carried out with food (earthworms) placed randomly at different locations, while the arena was sealed at all time in order for Catania to see every time the mole sniffed by measuring the difference in air pressure. When the mole was introduced, Catania observed how the mammal first sniffed a bit back and forth around its location then immediately zeroed in on its target, the food source, on a direct path.

“It was amazing,” he said. ”They found the food in less than five seconds and went to the right food well almost every time. They have a hyper-sensitive sense of smell.”

To see whether indeed stereo smell aided navigation, Catania blocked each of mole’s two nostrils at a time and repeated the test. When the left nostril was blocked, the mole would still be able to locate food, but its path towards it was veered to left. The same, only opposite, happened when the right nostril was blocked.

“This is strikingly similar to a landmark study of hearing in barn owls performed in 1979 byEric Knudsen and Mark Konishi at the California Institute of Technology, who found that blocking one of the owl’s ears caused them to misjudge the location of a sound source,” Catania said.

In the ultimate test that finally proved moles indeed posses stereo smell Catania reversed the mole’s nostrils  after he inserted plastic tubes in both nostrils that were reversed. Thus, the right nostril was sniffing air on the animal’s left and the left nostril was sniffing air on the animal’s right. When their nostrils were crossed in this fashion, the animals searched back and forth and frequently could not find the food at all.

Findings were published in the journal Nature Communications. [source]

ZME readers, is the mole cool or what? Discuss in the comments section below. 

The position of the 86 molecules within two maps of olfactory stimulus space. Map A is based on the way that we perceive odors (perceptual space) map B is based on the chemical structures of the molecules (physicochemical space). (c) Weizmann Institute

White smell: the neutral fragrance discovered by scientists

You’ve heard about white color and white noise, but know there’s a new neutral signal that balances the senses, the sens of smell to be more exact – white smell! Scientists at the Weizmann Institute have shown that white odor indeed exists, although it can’t be found in nature, after they created a mixture of various pure scents to convey the perception of olfactory neutrality.

White light is produced when an assortment of different wave frequencies meet, similarly for white noise as well as the distinct hum is produced by a combination of sound frequencies. For these to occur two fundamental conditions needs to be met: all the frequencies need to be of the exact same intensity and need to travel within a perceptual space – the visible spectrum for white light and the audible range for white noise.

The position of the 86 molecules within two maps of olfactory stimulus space. Map A is based on the way that we perceive odors (perceptual space) map B is based on the chemical structures of the molecules (physicochemical space). (c) Weizmann Institute

The position of the 86 molecules within two maps of olfactory stimulus space. Map A is based on the way that we perceive odors (perceptual space) map B is based on the chemical structures of the molecules (physicochemical space). (c) Weizmann Institute

This latter condition is very difficult to asses for our other senses, like smell. Could a white smell exist? This is  a question that has been puzzling scientists for a while and, until very recently, remained unanswered. Until, that is, a research team from the Neurobiology Department, led by research student Tali Weiss and Dr. Kobi Snitz, and supervised by Prof. Noam Sobel, took the challenge and successfully produced a white smell.

The scientists made their peculiar odor by mixing up to thirty different odors, from  86 different pure scents that represent a wide range of the kinds of things that we can smell (smell map), which were diluted in order to get the same intensity out of every odor. The human nose can distinguish thousands of sent molecules from flowery to putrid, however its dimensional spectrum is far from being mapped out neatly, as such a rather complicate maneuver was attempted.

The scientists created various blends that were presented in pairs to 150 volunteers or “professional noses”, and compared against a list of 146 different odor descriptions like “fruity” “etherish” “decayed” or “seasoning for meat”. It was found that the more different molecules were paired into mixtures, the bigger the chance that they would be rated as similar. Finally, the scientists found that blends that each contained 30 different odors or more were thought to be almost identical. It’s rather hopeless to describe white smell, because it doesn’t really smell like anything. This is incredibly confusing, and the participants in this study understandably did not know how to explain the scent.

“On the one hand,” says Sobel, “The findings expand the concept of ‘white’ beyond the familiar sight and sound. On the other, they touch on the most basic principles underlying our sense of smell, and these raise some issues with the conventional wisdom on the subject.”

White light equally activates the three color receptors of the eye – red, green and blue. Despite these new findings, the full extent of olfactory space remains unknown, but still it warrants a rephrasing of the common definition for the sense of smell. Rather than a sensor that detects individual molecules, our smell systems perceive whole scents.

The findings were reported in the journal Proceedings of the National Academy of Sciences (PNAS).

source: Weizmann Institute via Scientific American

Shorties: garlic as a guilty pleasure

Garlic is one of those things you can’t be indifferent about. You either love it, hate it, or love and hate it. This is exactly the reason why 100 Helsinki shoppers were interviewed and asked what they think abut garlic, and how much they are annoyed by it, compared to other social odors.

The most common belief was that garlic has a good taste, is healthy, but has an unpleasant smell. Users and non-users showed distinctly different belief patterns. However, it wasn’t nearly as unpleasant as researchers were expecting it to be. The most annoying social smells were considered to be sweat and alcohol, while garlic and aftershave were considered the least annoying.

Picture source

You know that smell metal has ? Well… that’s actually human smell

Whenever you catch the scent of a coin, a piece of iron or anything else metallica, it always seems to have pretty much the same smell. So what’s up with that? I’ve asked myself that a dozen times, but fortunately, so did Dietmar Glindemann of the University of Leipzig, Germany, and his co-workers. Their conclusion? It’s not the metal you’re smelling.

What they found is that the pelicular odour comes from chemical compounds from your skin (or whoever was touching the object) that are transformed instantly when they come in touch with the metal.

“When a shopkeeper hands you a coin,” says Glindemann, “you’re smelling his body odour.”

Well now… that’s definitely… something

Body odour – now essential for online dating!

So, you’ve been talking with him/her on  the Internet for the last four months: personality? check. sense of humor? check. good looks? check. Ready to meet you perfect half? Well, don’t forget about checking the body odor first!

This is not a joke, as weird as it may sound. It won’t be long before online dating websites will allow members to see if they would find their partner’s smell pleasant or would make them go away fast.  And yes, there is serious scientific background to support this initiative: our sense of smell proves to be highly important when choosing someone and it is all a matter of having strong, healthy children. But let’s not rush things.

Biologist August Hämmerli, who started this initiative through the company Basisnote, claims that no matter how well we get along with someone, an unpleasant body smell would make us go away in the end. So, all you have to do in order to avoid possible unpleasant situations is to take a fast saliva test (which is somewhat similar to a pregnancy test) in order to determine your body odor and then enter it as a code in a database; in a matter of seconds you can find out if the person you were flirting with would be pleasant to you and the other way around, if he or she has entered their own code, of course. The whole thing should last for 20 minutes and it’s far from being complicated.

But what factors are involved when liking someone’s smell? Well, it is not a matter of personal hygiene and expensive cologne, but of choosing a partner who is as different genetically from you as possible so as to have strong, healthy children. And even if having a child is the last thing that crosses your mind when flirting with someone, the whole process takes part unconsciously, as the nose’s sensitive receptors are always active.

Mice and other mammals were known to choose their partners by smelling them but until recently no one thought people do the same thing too.

During an experiment in the 90’s female students were given T-shirts that had been worn by men and they were asked to say which smell was the most attractive and which one the least. The man whose immune system differed the most was constantly chosen.

The genes of the MHC, the Major Histocompatibility Complex, which are the ones who carry instructions for various compartments of the immune system, are the ones to be analysed. They bind fragments of foreign proteins such as in the case of an infection and pass them to the defence system, which triggers a reaction. The more different MHC molecules one has, the more pathogents he or she can fight against – and so will the offspring.

In humans, there are about 100 variations of each of the 9 basic MHC genes, and they are the ones to give you your personal scent. The more you differ from your partner, the more he or she will like your smell.

Now the researchers are negotiating with several online dating platforms but they are confident that the idea will catch on quickly. But don’t forget to be charming and funny! This is only the last phase and nobody wants to know how a jerk smells like!

source: ETH Zurich.


It’s a fact – humans can smell fear too!

Since early childhood we’ve been told that if we are afraid of a dog which has turned violent, our furry buddy will “smell” our fear and we will eventually end up bitten. Not the most comfortable feeling ever…but as long as only animals can do it…
Many species are known to release a chemical signal in order to warn other members of the family in case something dangerous occurs; however, a study conducted by Denise Chen from Rice University seems to prove that we can do the same thing too.
When perceiving the world we use all of our senses, some being more important in this process. What researchers wanted to know is how important perceiving fear is.
“Fearful sweat” was collected from several male volunteers who had been given gauze pads for their armpits before being shown videos dealing with subjects which are known to be scary.
After this stage of the study, female subjects were exposed to chemicals from “fear sweat” and then shown different faces which varied from happy to ambiguous and scared. They had to indicate whether the face was happy or fearful by pressing buttons.
The smell of fear made women interpret the faces mostly as fearful in the case of the ambiguous ones, but didn’t change the results if the faces were clearly happy.
In conclusion, emotions caused by a sense can influence the way the same emotion is perceived through another sense, but only if the signals are not clear.

All these show that human sweat is a clear indicator of emotions too, humans being able to sense them and thus be influenced by these signals, mostly if other senses cannot be used.

Other species of animals use smell as a main way of communication when marking their territories or sending a message regarding a possible danger. The way we perceive smells and especially how important it is to us still remains a mystery, a mystery which seems to find a few answers.
source: Rice University