News in Science

Nostrils smell differently 2

Your nose can pick up smells. It turns out that each of our nostrils has erectile tissue inside. Many people seem to have a rhythmic Nasal Cycle, where this erectile tissue in one nostril swells, while it simultaneously shrinks in the other - and a few hours later, the swelling switches to the other nostril. This gives a different airflow in each nostril, which means that different smells get interpreted differently.

But there's still another factor that makes your nostrils interpret identical smells indifferent ways - it's how your nose is electrically wired to your brain.

Now apart from that swash-buckling character, Cyrano de Bergerac, the nose does not have a very romantic history. Very few poems are written to the nose, while thousands have been written to the eyes. All that happens to the nose is that you either pay through it, or you keep it to the grindstone.

Each day the nose cleans about 10,000 litres of air, which has to be filtered and air-conditioned, so that it won't shock the delicate lungs. The air has to be modified to the climate of a hot humid summer day - about 80% humidity and a temperature of about 35 degrees centigrade.

Inside the nose there are coarse hairs that strain out most of the particles bigger than 10 microns - that's about 1/7 the diameter of a human hair. Those particles smaller than 10 microns that get past the hairs on the nose, land on the sticky mucus membranes inside the nose, and on the tonsils and adenoids.

But, besides conditioning and cleaning the incoming air, the nose also does smells.

This recent research about how the nose is wired to the brain was done by Larry Cahill and colleagues from the Monell Chemical Center in Philadelphia, and the Center for the Neurobiology of Learning and Memory, and the Department of Psychobiology at the University of California at Irvine.

They showed that identical smells coming into each nostril are treated differently in the brain. This is because of how the smelling areas in each nostril are connected to your brain.

This research was done with 28 male and female volunteers from the undergraduate Psychology course at the University of California. The scientists exposed their volunteers to eight different odours that are also mildly pleasant - pineapple, coconut, maple, vanilla, peppermint, almond, lemon and anise. The volunteers were given these odours at two separate sessions, one week apart. The first time around, they smelt an odour through only one of their nostrils, but at the second, they smelt it with the other nostril.

When you sense a smell, the odour chemicals float into your nose, and land on the olfactory epithelium in each nostril. They stimulate the olfactory epithelium, which then sends electrical signals into the brain. If you look at the electrical wiring, you'll see that the electrical impulses from the left nostril go to the left side of your brain, while those from the right nostril go to the right brain.

Now this is a slightly "fuzzy" statement to make, but overall, your left brain tends to deal with language and words, while your right brain tends to deal with emotions. The scientists thought that this might influence how your brain processes identical odours that are presented to each of your nostrils.

They were correct. The scientists found that each side of your brain did process the information from each nostril differently. When odours came in through the right nostril, the volunteers thought that they were smelling something more pleasant than when the same odour came through the left nostril. That fits in with the right brain being involved in emotional processing.

But what does the left brain being involved in language do to odours? Well, the scientists checked for that by asking the volunteers to give a name to the smells that they were smelling. Sure enough, when the smells came in through the left nostril, the volunteers were more accurate in using their linguistic skills to give the correct name to the odour that they were exposed to.

So your brain tells you that odours are more pleasant if you sniff them through the right nostril, and your brain can name odours more accurately when you sniff through the left nostril.

I wonder what's going on in your brain, when you think that you smell a rat?

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