This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Nostrils. Your dog has them. Two of them actually. And you don’t give them any attention, do you? Sure, you might take your dog to the vet when you see gunk coming out of them, but on any given ho-hum day, you’re not giving your dog’s nostrils a second thought.
Of course, we all know I’m being entirely unfair. What more attention could you possibly give to your dog’s nostrils? There they are — one, two. To get a detailed sense of what your dog’s nostrils are up to, you can’t just eyeball it. Even researchers can’t eyeball it — instead, they videotape a dog’s nose and then analyze nostril activity frame-by-frame. This line of research leads to the publication of papers with excellent figures like this one:
Marcello Siniscalchi and colleagues from the University of Bari and the University of Trento in Italy are behind this excellent figure. I assure you, they weren’t trying to get close-ups of dog faces or recreate a beam-me-up, take-me-to-your-leader scenario. The video camera attached to a cotton swab with different odors helped the researchers investigate whether dogs use a particular nostril (the right side or the left) when investigating different smells. While there are many ways to discern how dogs interpret the different stimuli they encounter every day, nostrils could be another (albeit probably less expected) way in.
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Here’s what happened in the study: 30 mixed-breed dogs were presented with six different odors a number of times. The odors were chosen because they differed “in terms of familiarity and emotional valence” – including some things dogs would be gung-ho about, others not so much. The six odors were the smells of 1) dog food, 2) vaginal secretions from a healthy female dog in oestrus, 3) lemon, 4) a swab with nothing on it, 5) sweat from a known veterinarian, and 6) adrenaline. You can imagine that a dog might be pretty interested in the first two odors and find them nonaversive. On the other hand, the smell of a known veterinarian and adrenaline could be more noxious (although vet visits certainly don’t have to be noxious. And visit the end of the post* for how the smell of a veterinarian was put on the cotton swab).
Over the course of a few weeks, the dogs smelled the different scents a number of times, and essentially voted with their nostrils. When presented with the potentially noxious stimuli (the vet and the adrenaline), dogs “showed a consistent right nostril bias,” meaning they started investigating with the right nostril and stayed investigating with the right nostril over subsequent presentations. On the other hand, when presented with potentially nonaversive stimuli, like the food and the vaginal secretion, dogs initially investigated with their right nostril and then shifted to their left.
Although dog nostril research (if you want to call it that) is in its infancy, this difference in nostril use is something to write home about as it could indicate something about a scent’s valence (novel or familiar; positive or negative) as well as how scents are being processed in a dog’s brain. The researchers describe the olfactory neural pathway to the brain — “in mammals the olfactory system ascends mainly ipsilaterally, with most receptor information from each nostril projecting, via the olfactory bulb, to the primary olfactory cortex in the same hemisphere (Royet & Plailly 2004).” Essentially, what goes in the right nostril is being processed on the right side of the brain, and what goes in the left nostril goes to the left side. Lateralization research suggests that the right hemisphere is often involved in investigating novelty and is also associated with “intense emotions, such as aggression, escape behavior and fear,” while the left hemisphere is more focused on routine investigation and categorization, approach behavior, and positive emotional valence. The researchers’ findings are consistent with those general principles. Dogs tended to begin their investigation of the different scents with their right nostril (novelty), and they continued to investigate the potentially arousing stimuli -- like the vet odor and adrenaline -- through the right nostril. But over repeated presentations of nonaversive stimuli -- like the food and smell of another dog -- dogs switched to the left nostril.
Did you already get out the video camera to start taping your dog’s nostrils? I completely understand. Do I want to know which nostril dogs use when they first meet me? Of course I do. Do some dogs jump in with the left nostril while others start with the right? And if so, when do they switch to the left? So many nostrils, so little time.
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* How to put the smell of a veterinarian on a cotton swab: “The veterinarian was instructed not to use deodorant/antiperspirant for 2 days before the experiment … and to take only a shower on the morning of the experiment. On the day of the collection, the cotton swab was placed under the armpits of the vet for 10 min and then stored at -80 C until testing (several samples were collected).”
Want more on lateralization in dogs? Here you go:
The authors of this study have a chapter in the recent edited volume, The Social Dog, 2014. Eds. Kaminski and Marshall-Pescini. Over at Do You Believe in Dog?, Mia Cobb covers research into other methods to assess laterality in dogs.
This concludes the March 2015 Dog Spies Nose-a-thon! In this series, Part 1: This Month, Step Inside the Dog’s Nose, Part 2: Dog of the Dead: The Science of Canine Cadaver Detection, and Part 3: Three Reasons Not to Leave a Dead Body on the Carpet.
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Images:Flickr creative commons license; Siniscalchi et al., 2011. Animal Behavior, Elsevier. Figure 1. Schematic representation of the testing apparatus.
Reference
Siniscalchi M., Anna M. Pepe, Salvatore Dimatteo, Giorgio Vallortigara & Angelo Quaranta (2011). Sniffing with the right nostril: lateralization of response to odour stimuli by dogs, Animal Behaviour, 82 (2) 399-404. DOI: http://dx.doi.org/10.1016/j.anbehav.2011.05.020