Have you ever wondered what makes you right- or left-handed? Well, in humans and other mammals, the brain is divided down the middle, or ‘lateralized’. One of the effects of this is that people can be right-handed or left-handed (having better motor skill with one hand or the other). This is because one half of the brain controls these motor movements more so than the other half. People also tend to be dominant with one eye over the other (if you want to know which one you are, see my note at the end).

But what about other animals? Dogs predominantly use their right ears when listening to other dogs, but use their left ears when hearing threatening stimuli (like a thunderstorm). However, as anyone who has owned a dog will know, the sense they seem to rely on most is that of olfaction (smell). So are dogs right- or left- nostrilled?

In a recent study1, scientists gave 30 mongrel dogs different smells to sniff that they might encounter in their environment. I’d imagine that coming up with these smells must have been a fun task. The ones the scientists went for were: dog food, the sweat from the dog’s vet, lemon, adrenaline, vaginal secretion from a female dog, and finally just the cotton swab without any smell on it. They let the dogs sniff these smells seven times, over a period of a few weeks.

With the smells that were either neutral or ones that dogs liked (food, lemon, vaginal secretion and cotton swab), the first time dogs sniffed them, they did so with their right nostrils. However, as time went on and they encountered the smells more, they then switched to their left nostrils.

In mammals like dogs, the right nostril connects to the right hand side of the brain, and the left nostril with the left side. The fact that dogs smell with their right nostril first implies that the right side of the brain is involved first. This is thought to be because the right-hand side of the brain deals with novel information (in this case, a new smell), and then once the dog has become accustomed to the smell the left side of the brain takes over more, as this side handles more familiar stimuli.

However, for the other two smells (the vet’s sweat and adrenaline), that perhaps may not be quite as welcome to a dog, the dogs always smelled them with their right nostril. Even though the smell of the vet would be as familiar to the dogs as perhaps dog food or the smell from a female dog, it must have been more stressful to the dogs (as any person who owns a dog knows, taking it to the vet’s generally isn’t a relaxing event for anyone involved). The fight-or-flight response is mainly dealt with by the right side of the brain. Therefore, even though these smells became as familiar as the other ones did, they elicited enough strong emotions like fear to continue being processed by the right-side of the brain (and therefore the right nostril).

There is an interesting consequence of this work which might not be immediately obvious. Knowing that dogs will sniff an odour differently depending on whether the smell is familiar or elicits fear could have a role in animal welfare. For example, if we want to know if a person scares a dog, consistent smelling with the right nostril could provide a clue, even without the other behavioural signals.

1Siniscalchi, M., et al., Sniffing with the right nostril: lateralization of response to odour stimuli by dogs, Animal Behaviour (2011), doi:10.1016/j.anbehav.2011.05.020

How to tell which of your eyes is dominant:

Hold your finger up about a foot away from your face, and look at an object behind it with both eyes. Now shut your left eye, then open it again and shut your right. Your finger should appear to ‘jump’ more with one eye shut than the other. If the ‘jump’ was larger with your left eye shut, then you have left eye dominance, and vise versa for your right eye.