Inspector Sniffing Nose
Our sense of smell is considered to be comparatively underdeveloped. Can we still locate smells with our noses alone? And do we even have a chance to train our smell performance?
I can't smell. Yes, fact, always has been and probably always will be. Why? I have no idea – after the third ENT doctor shrugged his shoulders, I gave up trying to find out and resigned myself to my fate.
For me, a non-smeller, it's a big mystery how "normal" people can perceive thousands of smells. On the other hand, it sounds understandable to me that you can see the direction from which the scent cloud is emanating. After all, we also locate sources of noise with our two ears, and we can see three-dimensionally through our two eyes. So why shouldn't our two nostrils make directional smelling possible?
But science needs hard evidence. Jess Porter, Noam Sobel and colleagues from the University of California at Berkeley set themselves the task of finding them. First they wanted to know whether the human sniffing organ alone is really sufficient to recognize a scent trail and then follow it. In full gear - equipped with eye mask, earmuffs, gloves and knee and elbow pads - the researchers had their test subjects crawl on all fours across a lawn (see accompanying video under "Media"). Incentive for the effort: The string to be sniffed gave off a fine chocolate smell. Three quarters of the 32 test persons were successfully lured onto the track.
To make sure that the facial oriel was really responsible, some participants repeated the procedure with their noses closed (don't worry, even though almost everything else was barricaded, the mouth wasn't). The result was impressive: nobody managed to follow the trail.
Next, Porter and co investigated whether their subjects improved their snooping behavior with practice. Two men and two women repeated the experiment three times a day for three days. And indeed, in the end it took them only half as long to cover the 10-meter distance as it did at the beginning. The scientists also have an explanation as to why: The faster the participants completed the route, the more often they sniffed.
In all experiments, the subjects involuntarily behaved like so-called macrosmatic animals – such as dogs – to which we generally ascribe a much better sense of smell than we humans do. The test subjects carried out the characteristic zig-zag search movement, which deviated less and less from the straight scent trail with increasing sniffing frequency.
The scientists also put forward the thesis that the comparatively shameful olfactory performance of Homo sapiens is at least partly due to our behavior and less to the reduced repertoire of olfactory receptors. What do we learn from this: If we humans only sniffed more often, we could make up for a lot compared to our four-legged companions.
So much for the observable behavior in directional smelling. Now the researchers wanted to elucidate the mechanism in more detail. Since they suspected that the comparison of the stimuli between the two nostrils could play a role, they blocked one nostril of each test person in the next run. And really, fewer participants managed to find the trail. Also, those who succeeded took longer to travel than before.
But that's not enough to prove that nostril matching improves directional smell, Porter and colleagues reasoned. Perhaps the poorer performance was simply due to the fact that fewer odor molecules were able to find their way into the nose when sniffing, or that the transmission of stimuli to the brain was disrupted. In a previous study, they found out that the olfactory stimuli from each nostril are routed differently to the brain.
So they devised a final twist on the experiment. This time the participants were allowed to strap what the researchers call a "nasal prism apparatus" in front of their noses. Freely based on the principle "make one out of two", it simulates a single nostril in the middle of the nose. And even with this, the test subjects were worse at detecting noses than with their normal two-nostril prongs.
With this result it should now be pretty clear that our olfactory organ has two openings for a reason and that our noses are really able to locate smells. Even if that doesn't apply to me - I'd like to believe it. In any case, my own small study produced a very similar finding: thanks to a characteristic sniffing movement, a colleague recently guided me unerringly to the room where the others were already celebrating with mulled wine.
