Dogs and humans live together, play together, show affection, communicate and love each other. We develop deep bonds with one another and feel that we understand each other fairly well. Yet, when we look closely into the world of senses, there are striking differences between us. Dogs and humans do not experience the world in the same way, Not even close! So when we take a walk with our dog and feel that we’ve shared a special moment with him, what have we really shared? We see in three-color vision, when dogs, like most mammals, only have receptors for two colors. They can also see ultraviolet light that is completely invisible to our human eyes (Douglas & al., 2013) and can hear sounds that are out of our hearing range (Heffner, 1983). When it comes to our sense of smell, the differences are so big that it becomes hard to even compare our two species. We are simply not playing in the same league! Humans have only a portion of odor receptors compared to most mammals and the area in our brain dedicated to analyzing smells is greatly reduced. Dogs on the other hand are ‘creatures of the nose’ as points out Dr Horowitz (2010). Wouldn’t their extreme sensitivity to smells also play a factor in their relationship with us? A recent MRI study shows that dogs do indeed respond differently when presented with the scent of a person they are familiar with (Berns & al., 2014).
The dog’s sense of smell is so much greater than ours, that it’s very hard for us to even imagine what their world is like. Consider the ability to smell the difference between two footsteps to deduct which way a person walked, or detecting a teaspoon of sugar in an Olympic size pool! A dog’s nose contains up to 300 million olfactory cells, when ours has only about 6 million. The part of the brain specialized in analyzing smells is also about 40 times greater in dogs than in humans. In addition, the way the air moves inside the nose is quite different. In dogs, a portion of the air that is inhaled, takes a detour to the back of the nose, in an area dedicated to olfaction. The air will then be filtered through several bony structures lined with olfactory receptors. And when dogs exhale, the air exits through the slits on the sides of their noses. As it swirls out, the air sweeps in new air into the nose. This allows the dog to sniff almost continuously while breathing. If that wasn’t enough, dogs also possess an organ that we don’t have at all: the vomeronasal organ, or Jacobson’s organ. This organ is specialized in the recognition of pheromones, the chemicals released to trigger mating behaviors in others (Tyson, 2012).
With such amazing abilities it’s no wonder that mankind has often relied on dogs to help find what we cannot see. From narcotics to bombs or fugitives, our police and military forces have worked with dogs for many years. Search and rescue dogs have saved countless lives of people buried under rubble or snow that no person or man-made tool could have found. In the past decade, many have expanded the use of the dog’s nose to the medical field. Dogs have proven to be capable of identifying different forms of cancer, such as melanoma, bladder, lung, breast, prostate and ovarian by sniffing breath, urine or tissue samples of patients (Moser & al., 2010). In recent years, dogs have also shown the ability to alert to hypoglycemia episodes of diabetic patients thus providing an additional layer of protection to those dealing with this very scary condition. As I now specialize in the training of such dogs, I witness first hand the difference that dogs can make in a person’s life when they put their nose to work. I have no doubt that in the years to come we’ll find many other ways that dogs can help us with their amazing olfactory ability.
Examples of how our dogs’ sense of smell can contribute to our lives are innumerable. But having such a powerful smell analyzer also impacts how the dog experiences the world. As dog lovers, it’s important to try to understand their perspective as much as possible so that we can also contribute to making their life better. In an attempt to understand the role of the canine super sniffer in developing social relationships with others, scientists from Emory University have trained dogs to lie down in an MRI while presented with different scent samples (Berns & al., 2014). We know that they can identify different people by smell, but could we find out how dogs feel about us by their reaction to our smell?
Studies suggest that when dopamine is released in the caudate nucleus in the brain in the presence of a stimulus, that animal expects a reward. In other words, when a dog perceives a situation, another dog or a person that has been previously associated with a positive experience, based on food or social bonds, the caudate is activated. That activation can be observed and measured by the MRI. So when presented with the smell of different people or dogs, it becomes easy to see which smells trigger the most reaction.
The results of this study show that of all scents presented, the familiar human scent was the one that elicited the strongest reaction. So not only did the dogs discriminate between that smell and the others, but the smell of a person they know was strongly associated with positive expectations. The activation of this region of the brain has been linked with the motivational state ‘seeking’ (Panksepp, 2004), so it triggers a desire to approach or consume. It’s interesting to see that in this experiment, the familiar person triggered this reaction, even over the smell of other dogs, familiar or not.
Although we can’t tell from these results whether this reaction to our smell is an inherited predisposition or a result of our lifestyle with the dogs, this study is yet another example of the amazing power of our dog’s nose. When we feed, play and generally care for our dogs, they learn to depend on us for all their physical needs and most of their social needs. It’s therefore not surprising that they develop deep emotional bonds with us. So even though we experience the world in different ways, the strength of the love our canine companions feel for us runs deep, from the olfactory bulbs all the way into the wrinkles and folds of the brain.
Jennifer Cattet Ph.D.