September 18, 2018
Written by: Katerina Placek
According to archaeological record, the dog was the first species to be domesticated by humans, with evidence of human-dog coexistence dating back 14,200-36,000 years.1 Evolutionary biologists argue that this lengthy history of coexistence led to ‘convergent evolution’ such that humans and dogs evolved similar traits like eye contact and other social-communicative skills beneficial to each species’ survival.2 Evidence from contemporary human-dog relationships reflects this history. 50% of all Americans and a shocking 75% of millenials (myself included) own a dog, and modern dog-owners increasingly consider dogs as family members or even children. In fact, profound emotional and psychological benefits of dog ownership have been reported, leading mental health care professionals to recommend emotional support dogs to patients. While both fact-based and personal accounts underline a strong human emotional connection to dogs, one question remains: does your dog love you in return? Read on to see how neuroscientists have begun to answer this question.
How do we know what a dog is feeling?
Neuroscientists know increasingly more about the science behind our thoughts and feelings, to which the entire field of cognitive neuroscience is devoted. In humans, cognitive neuroscientists have characterized the brain anatomy and functional dynamics underlying a myriad of phenomena including memory, decision-making, attention, and – important to the present topic – emotion. Neuroscientists are able to study emotions like joy, sorrow, and love in humans fairly easily due to the fact that humans have the unique ability to use language to tell us exactly how they are feeling at any given moment. Understanding how a dog is feeling, on the other hand, is much more challenging since they cannot communicate with us with words. In the absence of language, how can dogs relay their subjective experience of love to their owners? Do dogs even experience love the same way that humans do?
Dr. Gregory Berns of Emory University, a neuroscientist and dog-owner, is well known for adapting a popular technique from human cognitive neuroscience to seek the answers to these – and other – questions. As discussed in a few previous pennneuroknow posts, functional magnetic resonance imaging (fMRI) uses strong magnetic fields and intrinsic properties of oxygen molecules in the blood to visualize brain activity ‘in action.’ Since the brain regions involved in generating and feeling various emotions are known in humans, Dr. Berns reasoned fMRI could be used to infer dogs’ subjective experiences, given similarities between the anatomy of dog and human brains including regions important to subjective emotional experience (to learn more, see this publicly-available anatomic guide to the dog brain).
Dogs experience joy in response to their owners!
After being training to lie still in the MRI machine* (Figure 1), dogs completed specially-designed tasks during fMRI which allowed neuroscientists to gain insight into how dogs feel just from brain activity!
*Many treats were consumed in this process. Researchers worked with professional dog trainers to acclimate dogs to lie down inside the MRI machine for 20-30 minutes at a time during fMRI scanning. No restraints or anesthetics were ever used.
From initial experiments with their own pets, researchers first found that – like humans – dogs experience reward in a brain region called the caudate nucleus.3 The caudate nucleus (Figure 2) is one of the structures involved in the brain’s reward system, and its activity is related to positive emotions like pleasure and joy.4 Dogs showed increased activity in this region in response to owners’ hand signals associated with treats vs hand signals associated with no treats.
But do dogs enjoy their owners at least as much as they enjoy treats?
Rejoice, dog owners, because researchers found in a subsequent study that 13/15 dogs had equal or greater activity in the caudate nucleus for their owners’ praise vs a hot dog!5 Moreover, activity in the caudate nucleus predicted whether dogs would prefer walking to their owner to get praise or walking to get a hot dog without their owners present. This research finding makes sense when you consider that you can train dogs to “Leave it” (i.e. ignore a treat) and reward them for this behavior with praise (I’m proud, because my Jack Russell Terrier, Zoey, has mastered this!).
…And they experience more joy from humans than other dogs!
In addition their owners’ vocal praise, dogs also experience reward when smelling the scent of their owner – and they find their owner’s scent more rewarding than the scents of other dogs.6 Researchers presented five scents to each of the 12 dogs that participated in this study: self (i.e. the dog’s own scent), owner/familiar human, unfamiliar human, familiar dog, and unfamiliar dog. The olfactory bulb – the brain region that codes responses to smell – was activated to a similar degree to all five scents. However, the caudate nucleus showed differences in activation dependent on scent – the strongest activity recorded was when the dog smelled the scent of their owner or a familiar human!
But is it really love?
Ok, so this is more of a philosophical question, and depends on 1) if you are inclined to believe subjective feeling is authentically represented by brain activity, and 2) if you think the experience of reward approximates the experience of love. As a dog owner, I’m inclined to interpret the current cognitive neuroscience findings as affirmative – I know that when Zoey looks at me, she loves me.
Cover image: The author and her Jack Russell Terrier, Zoey. Photo courtesy of Yeri Song.
Figure 1: Berns, G. S., Brooks, A. M., & Spivak, M. (2012). Functional MRI in awake unrestrained dogs. PLoS ONE, 7(5), e38027. http://doi.org/10.1371/journal.pone.0038027
Figure 2: Image from Anatomography maintained by Life Science Databases(LSDB). Source: https://commons.wikimedia.org/w/index.php?curid=9809383
- Janssens, L. et al. A new look at an old dog: Bonn-Oberkassel reconsidered. Journal of Archaeological Science 92, 126–138 (2018).
- Range, F. & Virányi, Z. Tracking the evolutionary origins of dog-human cooperation: the ‘Canine Cooperation Hypothesis’. Front Psychol 5, 49 (2015).
- Berns, G. S., Brooks, A. M. & Spivak, M. Functional MRI in awake unrestrained dogs. PLoS ONE 7, e38027 (2012).
- Berridge, K. C. & Kringelbach, M. L. Pleasure Systems in the Brain. Neuron 86, 646–664 (2015).
- Cook, P. F., Prichard, A., Spivak, M. & Berns, G. S. Awake canine fMRI predicts dogs’ preference for praise vs food. Soc Cogn Affect Neurosci 11, 1853–1862 (2016).
- Berns, G. S., Brooks, A. M. & Spivak, M. Scent of the familiar: An fMRI study of canine brain responses to familiar and unfamiliar human and dog odors. Behavioural Processes 110, 37–46 (2015).