Functional magnetic resonance imaging (fMRI) is a research technique which measures blood flow or activation in different areas of the brain. The caudate nucleus is located near the center of the brain and is associated with the experience of reward. Studies exploring dogs’ responses to their human family members as well as humans’ responses to their romantic partners both show activation in the caudate nucleus, suggesting positive associations with loved ones.
Canine research involving fMRI is challenging due to the need for the dogs to stay completely still during the task. Researcher Gregory Berns and colleagues have worked to train dogs to conditions similar to the fMRI task so that they can stay completely still while completing the fMRI scan. You can watch a video detailing this training here. In the current research project (Berns et al., 2014), the dogs were also trained to remain still while presented with cotton swabs which were used to present different scents. Twelve dogs were exposed to scents of self, familiar dog (another dog in the household), unfamiliar dog, familiar human (human member of the household), and unfamiliar human in a randomized order. The researchers particularly looked for activation in the caudate nucleus, one area of the brain associated with the experience of reward. The caudate nucleus of the dogs was activated most strongly when the scent of the familiar human (member of the dog’s household) was presented, indicating that the dogs had the most positive associations with the scent of that person.
In the human fMRI research involving romantic love (Aron et al., 2005), the researchers investigated brain activity in 10 women and 7 men who self-reported being intensely in love with their partners. These participants were presented with photographs of their partners and a familiar (but not intensely loved) person of the same sex and age as their partner while undergoing an fMRI scan. Although these researchers investigated activation in many different parts of the brain, similar to the reactions of dogs, the caudate nucleus of the humans was also maximally activated when looking at the photo of their romantic partners versus the neutral person (other areas of activation included the right ventral tegmental area and the right postero-dorsal body). The authors of this article conclude that the activation in these reward-centered areas of the brain motivates us to focus on our romantic partners.
Berns and colleagues acknowledge that although dogs form strong attachments to humans, it is very difficult to objectively determine dogs’ emotional experiences and whether those experiences parallel human emotional experience. Although caudate activity is associated with positive expectations and rewards, Berns et al. caution that it cannot be explicitly inferred that this means the dog is experiencing a positive emotional state. The authors do state, however, that the caudate response is similar to the neurological responses of humans who are exposed to photographs of loved ones and specifically cite the research by Aron et al. (2005). Activation of similar brain areas in dogs and humans in response to loved ones is particularly noteworthy because the brains of humans and dogs differ in structure. Future research will be necessary to determine other commonalities between dogs’ and humans’ neurological responses.