Come across an image like this, and you’d be a weirdo not to investigate. Meet infrared thermography, a non-invasive way to visualize changes to body surface temperature. Thermographic video cameras not only produce images that would make Andy Warhol proud (or at least sue for infringement), but the tool allows researchers to assess physiological changes—and potentially emotional states—in a wide variety of species like distantly related BFFs Canis familiaris and Homo sapiens.

Think about it—physiological changes are part of the emotional response. When you are frightened, blood rushes away from your extremities to get your muscles ready to go, which means your extremities get cooler as your core gets warmer. Infrared thermography, which captures changes to body surface temperature, is going to pick this up. The tip of a scared person’s nose gets cooler (more blue) under an infrared camera, and studies find that when scared or distressed, rat paws and tails appear cooler, as do the outer parts of sheep and rabbit ears.

Dog ears recently caught the attention of Stefanie Riemer and colleagues at the Animal Behavior, Cognition and Welfare Research Group (Twitter) at the University of Lincoln, UK. They wanted to know whether dog ears would show differential blood-flow patterns in response to something good as well as something less good. Dogs participated in a separation test where they were briefly alone in a novel environment (which elicits short-term distress) and then reunited with people (typically a positive experience). The separation, the researchers assumed, would be associated with negative emotions and therefore cooling of the ears, while being reunited with people (excellent!) would show an increase in ear temperature. The study appears in the current issue of Physiology & Behavior

Six dogs (and their ears) were included in the study, including Cuddles the Rottweiler and Reuben the Jack Russell terrier / Lhasa Apso cross. Milo, Lily, Olga, and Chloe also participated (and now you know just how much I enjoy reading the names of dog subjects. If you are a researcher and considering leaving the names out, please reconsider. I mean, Cuddles the Rottweiler? Come on). 

A few more dogs participated in the study, but unfortunately they could not contribute to the final analysis. “[Unsuitable] fur structure,” the researchers explain, meaning “ears too densely furred or unevenly furred/fluffy.” No Fluff-Balls Allowed is what I’m hearing. If infrared thermography takes off, we may see some interestingly shaven dogs (although the researchers admit dog owners might not be up for this sort of, uhm, grooming).

Back to the ears. The six pairs of ears in the study “performed” as expected: ear temperature showed a pattern of decreasing when dogs were alone, suggesting “that isolation stress is associated with reduced ear temperature"; when reunited with people (the good stuff), ear temperatures increased. Under the watchful eye of infrared thermography, ear temperature could be used to assess positive or negative affective states in dogs in other—less straightforward—contexts.

Not all body parts under the thermographic lens are as clear-cut. Take the eyes. Tiziano Travain and colleagues from universities in Parma and Milan, Italy exposed dogs to something good (receiving food) and something less good (undergoing a vet exam).* Eye temperature increased in both contexts, suggesting that, while changes in eye temperature could indicate general arousal, it might fail to indicate valence or direction of arousal (like whether the emotional state is positive or negative).

In conclusion, I’m just kidding! The study found that dog ghosts are all around us. Don’t worry. They are friendly. Happy Halloween.

Figure 2. “Example of the view of the thermographic camera (settings at gray-scale for subsequent analysis; brighter colors correspond to higher temperatures as indicated on the bar on the right).” Credit: Riemer et al. 2016

* “Fear or anxiety is more than just an emotional problem for pets—it has the potential to cause many serious physical health problems and contribute to several others,” explains Valarie Tynes, DVM, DACVB, in an article on DVM360. The issue is real: Zazie Todd at Companion Animal Psychology recently reviewed a study finding Just How Stressed Dogs Are at the Vet's, and in another post she offers tips for Less Stress at the Vet for Dogs and Cats, and Should Vets Give Treats to Pets? (Yes. Yes, they should). A movement is growing among veterinary professionals to decrease fear and stress in veterinary settings. For example, Fear Free is a new initiative promoted by Marty Becker, American's Veterinarian, to reduce anxiety triggers and foster safer veterinary environments.

Riemer S, Assis L, Pike TW, Mills DS. 2016. Dynamic changes in ear temperature in relation to separation distress in dogs. Physiology & Behavior, 167, 86—91.

Travain T, Colombo ES, Heinzl E, Bellucci D, Prato Previde E, Valsecchi P. 2015. Hot dogs: thermography in the assessment of stress in dogs (Canis familiaris)—a pilot study. Journal of Veterinary Behavior, 10, 17—23.

Travain T, Colombo ES, Grandi LC, Heinzl E, Pelosi A, Prato Previde E, Valsecchi P. 2016. How good is this food? A study on dogs’ emotional responses to a potentially pleasant event using infrared thermography. Physiology & Behavior, 159, 80–87.