Flies That Can’t Smell just Can’t Tell

Just how important is a good sense of smell in matters of romance? Well, for male fruit flies, it’s so vital that the absence of just a single olfactory gene renders them as indiscriminate in matters of courtship as my cousin Freddie (no offense, Freddie).

Scientists at Duke University Medical Center have found that male fruit flies without the gene Gr32a, a critical pheromone receptor, were sexually outperformed by four to one in comparison with normal male competitors. They also tended to court females which had been doused with male pheromones, behavior not observed in normal fruit flies because females which smell of male pheromones have presumably already mated. In fact, the hapless Gr32a-impaired flies were just as happy to court the male competitors themselves.
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Lemurs are Double-Dealing Little Stinkers

Considering the important role of scent in nature, it’s no surprise that many species have evolved some downright sneaky tactics to disguise, diminish, or enhance their odor footprints. Male pandas will urinate onto a tree while performing a handstand so as to leave the highest (thus most dominant) mark. Dogs, to the horror of their owners, tend to mask their scent by enthusiastically rolling in some of the most foul-smelling substances imaginable. Humans shell out millions to eliminate the natural odors of our bodies in favor of odors we consider more attractive.

Lemurs, though, distant primate cousins of ours who split from the family tree before the monkeys and apes parted ways, may well have cornered the market on sophisticated scent-treachery. According to a new study conducted by Leonardo Dapporto at Florence University, each of these bi-scentual little guys produces two completely separate scents–one from each hand–and these scents are as distinct from one another as that of two separate lemurs.

It’s a discovery unprecedented in scent research, and the question is still open as to why dual-odors would evolve in a single individual. One answer is offered by Ron Swaisgood, a behavioral ecologist at the Zoological Society of San Diego, who suggests the opposing scents may enable lemurs to mislead neighboring groups and predators as to the size of their colony. An even more intriguing possibility is that having two scents might allow the lemur to communicate through scent with a sophistication previously undreamed of, weaving complex tapestries of odor as varied as the shades an artist might create from two colors of paint.

Stench Soup and Other Winning Recipes

Betty Crocker, she’s not. And when the US Department of Defense approached Pamela Dalton of the Monell Chemical Senses Center to create a recipe for the Foulest Malodor on Earth, she took to the task with a devilish passion.
Her “Burnt Hair” formula smelled pretty bad. “Who Me?”–which combined natural gas odorant with a sort of spoiled mushroom aroma–was downright nasty. “Bathroom Malodor”–a fecal odor spiced with rotten eggs and decaying rodent–was disgusting enough to get Dalton cursed in several languages by her multi-ethnic test group. But it was a worst-of-the-worst proprietary blend that took the prize: “Stench Soup” smells so perfectly horrible that it sends the stomach lurching, the eyes tearing, and blows every other thought right out of the mind.
“That one takes over every aspect of your consciousness,” Dalton says proudly, adding that she can think of several uses for her stinky concoction besides non-lethal warfare. “Odors are one of the quickest ways to get people to move away from something. I’ve evacuated our building on several occasions because we’ve had an odor escape.”

No Coffee For Me, I’ll Just Sniff Yours

It may not be the caffeine that makes sleepy people crave a cup of Java. According to a team of scientists led by Yoshinori Masuo at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan, just the smell of coffee may be enough to reverse the effects of sleep deprivation on the brain.

An examination of the brains of sleep-deprived mice revealed reduced levels of mRNA (messenger molecules that indicate when a gene is being expressed) for eleven genes important to brain function. When the mice were exposed to the aroma of coffee, the mRNA for nine of the genes was restored to near-normal levels–and pushed to above normal levels for two!

If the same genes are suppressed in sleep-deprived humans, says Masuo, it may explain why people feel bad when they haven’t had enough sleep. Further, that gene reactivation could explain why people love the smell of coffee. His team is currently working to identify the specific molecules in coffee aroma that affect gene expression, in hopes of pumping them into factories to help revive tired workers, thus eliminating the need for “coffee breaks.” Is nothing sacred?

Developing a Nose for Danger

A whiff of diesel fuel can trigger a nasty flashback for a soldier suffering PTSD. The smell of peanut butter might bring on physical nausea for someone who has experienced a violent allergic reaction. Emotionally charged situations make us hypersensitive to olfactory cues and, according to a March 2008 study conducted by Northwestern University, our sense of smell actually becomes sharper when something bad happens.

Twelve volunteers were exposed to three sets of odor molecules, two identical and a third with the same chemical formula but structured to be the “mirror opposite,” a distinction which is normally undetectable to the noses of humans. Asked to identify the odd third odor, the volunteers guessed correctly about one third of the time–just as random chance would dictate. After being subjected to a mild electric shock while smelling the odd odor, however, they were able to distinguish it 70 percent of the time. MRI scans supported these findings, showing physical changes in how the main olfactory regions of the volunteers’ brains stored the shock-linked scent. “This is an incredibly unique study,” said Dr. David Zald. “We’re talking about a change in our perceptual abilities based on emotional learning.”

Does This Make Me Smell Fat?

A floral-spice scent may be “the olfactory equivalent to vertical lines”, said Chicago neurologist Dr. Alan R. Hirsch following his study into the effects of scent on body-weight perception.
199 male volunteers were divided into four sub-groups (including one control group) and charged with the unenviable task of guessing the weight of a female model with only one variable–her scent. The results? Neither citrus floral nor sweet pea & lily of the valley seemed to affect the men’s perception at all, but the floral & spice mixture reduced the men’s estimates of the model’s weight by an average of 4.1 pounds.
Interestingly, the perfume trick seems to work only for women and only on men. “Either women are too adroit at guessing other people’s weight,” says Hirsch, “or men are just easily influenced by how a woman smells.”

Don’t Stink to Strangers

The particular areas of the brain stimulated by visual and audial social input (such as recognition of familiar faces and voices) were isolated long ago. But it was not until 2007 that Dr. Johan N. Lundstrom, an olfactory scientist at the Monell Chemical Senses Center in Philadelphia, successfully demonstrated similar “specialized neuronal networks” for odor input.

By monitoring the brain activity of volunteers while they sniffed cotton pads that had been allowed to ferment for seven days in the armpits of friends and non-friends, Lundstrom found that smelling a friend’s body odor activated neural regions known to react to familiar stimuli (like a favorite song). The smell of a stranger, however, activated the “amygdala and insular” regions, previously demonstrated to react to fearful stimuli (like images of snakes).

What’s That Smell? Just Check Your Map!

There’s no real challenge in recognizing physical relationships within four of the five senses: We can see, hear, taste, and feel–respectively– the range between black and white, high and low, bitter and sweet, rough and smooth. But what about smell? Odor molecules are much more difficult to pinpoint, and the traditional view has been that smell is a subjective experience, strictly in the “nose of the beholder.”

Not so, say researchers at the Weizmann Institute of Science. As with the other four senses, smell is governed by universal laws which determine how our brains perceive them. By generating a dataset of around 1600 chemical characteristics for each of 250 odorants, the research team created a multidimensional map that charted the distance between one odor molecule and another, ultimately boiling down the traits to around 40. When the “smell map” was compared to previously published olfactory studies involving a variety of species, the scientists found that, the closer the physical distance between any two smells on the map, the more similar the neural patterns of the animals. The researchers also used the map to calculate the neural patterns that would be aroused in animals by 70 additional odors and found that their predictions closely matched the experimental results.

By pinpointing the relative distance between various odors, the scientists hope to help unravel the basic laws underlying our sense of smell and potentially enable odors to be digitized. Wonderful news for advertisers in this multi-sensory era, who may soon find their Metric Smell Map as valuable a tool as their trusty Color Wheel.

OppoScents Attract!

A bizarre 1995 experiment conducted by Claus Wedekind and colleagues at the University of Bern in Switzerland asked female students to sniff T-shirts that had been worn for three days by male volunteers and rate them for attractiveness. The DNA of the men and the women was then analyzed, in particular the genes, which build a part of the immune system. The infamous Stinky T-Shirt Study showed that women were biologically programmed to sniff out men with immune systems vastly different from their own, thus creating a wider gene pool and more robust offspring. Interestingly, this preference was reversed in women who were taking oral contraceptives (which mimic pregnancy). Women on the pill preferred the scent of men with very similar genetics, such as close relatives, who would be more likely to help her care for the baby.

Shop and Smell the Roses

Shoppers — actually 689 West Chester University students engaged in a shopping experiment — underestimated the amount of time they spent shopping by 26% when exposed to the pleasant aromas of clementine and vanilla. They overestimated it by 40% when the room smelled of galbanum, a vile aroma that reminded the professor, Jack Gault, of a combination of skunk and rancid oil.

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