Is the Dog's Brain Tuned to Love People?
Is there a "feel good center" in the dog's brain that is specific for humans?
Posted Oct 28, 2014
Most dog owners believe that their pets have a strong affection for them, perhaps something that we could describe as love. Some scientists believe that we have systematically bred dogs so that they are predisposed to form a close bond with human beings, and there is even some evidence that suggests that dogs may love people more than they love other dogs (click here to read about that). Dr. Gregory Berns, a neuroscientist at Emory University in Atlanta Georgia, was intrigued by such findings and decided to see if it was true that dogs had stronger feelings for humans than for animals of their own species*. He decided to use a very high tech objective measure to answer the question, namely the response of the canine brain.
In previous investigations Dr. Berns had already shown that it is possible to train dogs to hold still while an fMRI scan was being made of their brain. This is a difficult task, not only because it requires a dog to remain motionless in a confined space for a period of time, but because MRI machines make a lot of noise, such as whirring gear sounds along with loud clanks and bangs, and these might be expected to startle a dog and cause him to move. Thus extensive training is needed to use this equipment with dogs.
Berns and his co-investigators, Andrew Brooks and Mark Spivak, decided that they would test the emotional response of dogs to various significant odors associated with humans and canines. Specifically they would use three dog related scents, one from the dog himself, one from a familiar dog who lived in the same household with him, and one from an unfamiliar dog. They also chose to use two human scents, one from a person that the dog was familiar with (generally a spouse or a child in the family, but not the dog's handler who would be in the room while the dog's brain was being scanned) versus an unfamiliar human scent. The examples of scents were obtained on the morning of the scan. The odors were collected on sterile gauze pads and sealed in plastic envelopes. The human scents were collected from the armpit (sans deodorant) and the dog scents were collected from a region near the genitals.
The investigators chose to pay special attention to two areas of the brain. One was the olfactory bulb, since it is the primary area in the brain in which scent information is processed. This could answer the question as to whether in our long association with and selective breeding of dogs, we have actually tuned the dog's sense of smell to be more sensitive to human odors. The second area of the brain that they zoomed in on was the caudate nucleus. If you look at a dog's brain you can't see the caudate nucleus because it is deep in the middle of the brain and obscured by layers of cortex. It can be seen if you cut the brain in half lengthwise, as in the diagram here, or if you use a brain scanning technique like the MRI.
Because most brain regions have multiple functions it is not usually possible to link activity in one region with a particular cognitive or emotional state in an individual. However, perhaps more than any other region of the brain, activity in the caudate nucleus seems to be specifically triggered by rewards, and this includes both the basic rewards like food and social interactions, but also, at least in humans, by complex rewards like money and music, which may have learned components. Some researchers have suggested that activity in the caudate nucleus can be triggered just by the anticipation of something pleasant about to happen. In other words we could probably call this the "feel good center" of the brain.
If we start off with an analysis of the response of the olfactory bulbs to the scents of humans and dogs, the researchers found little to differentiate the responses. This suggests at least at this basic level the dogs nose is not specially tuned to detect humans. Not too far away from the olfactory bulbs however the team found that there is an area in the front part of the dogs cortex that has greater activity when presented with familiar scents, rather than unfamiliar. In addition this whole area responds more vigorously when the scent is from a dog rather than a human. However this area has never been shown to have any involvement with emotions or feelings, and probably has more to do with recognizing and identifying what is being smelled.
Since the real question has to do with what the dogs feel for humans and dogs the researchers knew that the answer would come from the activity in the caudate nucleus. Here the largest response was to the familiar human. This not only verified that the dogs recognized a familiar human, but also that the dog most likely had some affection for that person along with the anticipation that their interactions with that person would be pleasant and rewarding.
These results are interesting, but they raise questions as well. Was the brain response in the caudate nucleus a result of selective breeding, which would mean that the dog's brain was tuned specifically to respond positively to humans, or was this due to the social environment that the dog was living in, which would mean that the brain had become especially responsive to specific individuals. Here the answer comes from the fact that the largest response was to the familiar person and much less so to the unfamiliar human. It seems that the tuning of the dog's brain for affection toward humans that now exists has most likely come about because the dog was raised and lives in a loving and nurturing environment. Thus the specific people that the dog knows are associated with good things and pleasant anticipations, and anything that reminds them of these people lights up the reward center of their canine brain.
Stanley Coren is the author of many books including: The Wisdom of Dogs; Do Dogs Dream? Born to Bark; The Modern Dog; Why Do Dogs Have Wet Noses? The Pawprints of History; How Dogs Think; How To Speak Dog; Why We Love the Dogs We Do; What Do Dogs Know? The Intelligence of Dogs; Why Does My Dog Act That Way? Understanding Dogs for Dummies; Sleep Thieves; The Left-hander Syndrome
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* Data from: Gregory S. Berns, Andrew M. Brooks & Mark Spivak, Scent of the familiar: An fMRI study of canine brain responses to familiar and unfamiliar human and dog odors. Behavioural Processes (2014, in press), http://dx.doi.org/10.1016/j.beproc.2014.02.011