The common wisdom that dogs can smell fear doesn’t give dogs full credit to the nuances of their ability to sense emotion through their noses. A recent study titled “The dog nose “KNOWS” fear: Asymmetric nostril use during sniffing at canine and human emotional stimuli” examined dogs’ tendencies to sniff various substances with the right or the left nostril. Exploring this side bias may seem like looking at random details, but the side of the nose used to sniff something tells us a lot about the dog’s emotional reaction to the odor. The use of one side of the body indicates a differential use of one side of the brain or the other, which is a clue to the dog’s emotions.

The left side of the brain processes more positive emotions such as happiness and excitement as well as stimuli that are familiar. The right side of the brain tends to take over when a dog is processing negative emotions such as sadness or fear as well as novel stimuli. In general, the right side of the body is controlled by the left hemisphere of the brain and vice versa. However, the nose is an exception; the right nostril sends information to the right side of the brain to be processed and the left nostril sends its information to the left side. The findings of this study suggest that the pathways used to process various olfactory stimuli are dependent on more than just whether they elicit negative or positive feelings.

Eight odors were tested—four from dogs and four from humans. The four human odors were collected as sweat from donors who were joyful, fearful, physically stressed, or in a neutral situation. The joyful and fearful states were elicited by movies, and the physical stress odor was collected after donors ran for 15-minutes. The four canine odors were collected from dogs who were happy following a play session with the guardian, stressed by isolation in an unfamiliar place, disturbed by a stranger approaching the car, and dogs who were asleep. The dogs who “donated” odors were different from the dogs whose sniffing behavior was studied.

To further explore the phenomenon of side bias in sniffing, the guardians of the dogs in the study filled out a questionnaire related to each dog’s temperament. During the study, dogs were led to a video camera under which was mounted a Q-tip saturated with various odors. The videos captured the dog’s sniffing behavior so that it was possible to determine a laterality index for each dog for every odor based on the amount of time spent sniffing with each nostril. A laterality index of 1.0 indicated exclusive use of the left nostril and negative 1.0 indicated exclusive use of the right nostril. Dogs’ cardiac activity was also recorded during the tests of each odor.

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I’m sure it’s the science geek in me, but I got a kick out of reading the sentence, “Results for nostril use are shown in Figure 2.” Three of the odors elicited consistent sidedness in nostril use and five of them did not. Dogs more frequently used the right nostril to sniff the canine isolation odor. They more frequently used the left nostril to sniff the human fear odor and the odor from human physical stress.

There were two ways in which the results of the questionnaire were correlated with the laterality pattern for a particular odor. The higher a guardian ranked the dog’s fear/aggressiveness to other dogs, the more likely that dog was to use the right nostril for sniffing the disturbed canine odor. This suggests that individual differences in emotional arousal and perhaps even in temperament influence asymmetries in sniffing behavior. Dogs with higher scores for predatory behavior used the left nostril more for sniffing the odor that came from physically stressed humans. This makes sense when we consider that it is structures in the left side of dogs’ brains that are involved in predatory behavior.

Dogs’ brains are every bit as amazing as their noses, as research about both of them reveal!