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You Really Can Smell Fear...Plus Other Things Your Nose Knows

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"Subtle smells can change your mood, behaviour and the choices you make."

Your sense of smell is more valuable than you thought. It not only links to memories, but it can influence decisions you make, experiences you have and your perception of others.

First, watch as this New Scientist reporter, Catherine de Lange, gets down on all fours to see if she can emulate one of the best known sniffers -- a dog:

As you can see, she gets well of course at first -- there were so many other distracting smells. But when she really focused the second time, she was able to follow the 10-meter cinnamon oil trail laid in a public park in London.

She notes in her article about this 'unsung sense' that it is well-accepted humans don't have great sniffers compared to dogs. But developing science she writes is finding humans may be better at smelling than we thought:

According to a spate of recent studies, our noses are in fact exquisitely sensitive instruments that guide our everyday life to a surprising extent. Subtle smells can change your mood, behaviour and the choices you make, often without you even realising it. Our own scents, meanwhile, flag up emotional states such as fear or sadness to those around us. The big mystery is why we aren't aware of our nasal activity for more of the time.

Noses have certainly never been at the forefront of sensory research, and were pushed aside until recently in favour of the seemingly more vital senses of vision and hearing. "There has been a lot of prejudice that people are not that influenced by olfactory stimuli, especially compared to other mammals," says Lilianne Mujica-Parodi, who studies the neurobiology of human stress at Stony Brook University in New York.

Early scientists felt that humans had an inferior sense of smell compared to other animals because a smaller portion of the brain was devoted to this sense. But, newer brain scans, have shown that more of our brain is used from smell than previously thought:

Although we may have fewer types of receptor than other mammals, Charles Greer at Yale University has shown that the human nose and brain are unusually well connected, with each group of receptors linking to many more neural regions than is the case in other animals. That should give us a good ability to process incoming scents.

Once researchers began looking, they found the nose to be far more sensitive than its reputation suggested. One study, for example, found that we can detect certain chemicals diluted in water to less than one part per billion. That means that a person can detect just a few drops of a strong odorant like ethyl mercaptan in an Olympic-sized pool.

According to New Scientist, research is also making the link between smell and memory more clear:

The power of smell will be no news to estate agents, who often advocate the smell of baking bread or brewing coffee to promote the sale of a house. But there are more subtle and surprising effects too. For instance, when Hendrick Schifferstein from Delft University of Technology and colleagues pumped the smell of orange, seawater or peppermint into a nightclub, the revellers partied harder - they danced more, rated their night as more enjoyable, and even thought the music was better - than when there was no added scent (Chemosensory Perception, vol 4, p 55). Rob Holland and colleagues at the University of Utrecht in the Netherlands, meanwhile, have found that the hint of aroma wafting out of a hidden bucket of citrus-scented cleaner was enough to persuade students to clean up after themselves - even though the vast majority of them hadn't actually registered the smell (Psychological Science, vol 16, p 689).

In addition to research showing how smell affects decision making and even finding a mate (think pheromones), the thought that someone can smell fear is also supported by science. To help show this, scientists took sweat samples for subjects who were about to go skydiving for the first time, and a second sample from the same subjects when they were just running on a treadmill. Scientists found that a portion of the brain lit up when the test subjects who were asked to smell the samples took a whiff the skydiving sample, as opposed to the treadmill sample.

So, before you discount your schnoz for the more "favored" senses of sight and taste, consider the impact of smell that you may not even realize.

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