When dogs see human faces, a region of the brain called the temporal cortex becomes activated, a new study published to PLoS ONE shows.

The invention of functional magnetic resonance imaging (fMRI) in the 1990s revolutionized how scientists study the brain. The surprisingly simple technique grants a glimpse inside the skull, allowing researchers to examine blood flow within the brain, which is intimately linked to brain activity. Want to know which regions of the brain are activated in response to varying stimuli? You simply follow the blood.

For more than three decades, fMRI has fueled a great many studies leading to a number of incredible insights about the human brain. But only recently has the method been adapted to study man's best friend. In 2012, Emory University neuroscientist Gregory Berns trained two dogs, including his own canine companion Callie, to sit still and remain attentive within an fMRI scanner. He then cued the dogs with the indication of a food reward (a delicious hot dog) and watched as an area of their brains called the caudate nucleus "lit up."

In the current study, researchers from the National Autonomous University of Mexico adopted Berns' methods and trained seven dogs -- five Border Collies, one Labrador Retriever and one Golden Retriever -- to sit still in a "sphinx" position within an fMRI scanner, their ears adorably adorned with soft ear muffs to protect them from the loud, startling sounds of the machine.

When each canine's training was complete, the researchers presented the dogs with pictures of either human faces or everyday objects and closely watched the canine's brain activity. While everyday objects did not induce much activity at all, human faces elicited a ton of activity (see figure below), primarily in the bilateral temporal cortex, but also to a smaller extent in the frontal cortex, the caudate nucleus, and the thalamus.

"This portion of the temporal cortex in dogs could be anatomically and functionally similar to regions found in other species, like humans, non-human primates and sheep, which suggests a high degree of evolutionary conservation of the ventral visual pathway for face processing," the researchers write.

"The recognition of human faces by dogs could be an essential factor for establishing attachment with humans," they add.

The experiment confirms a similar study published last year by Berns and his colleagues, which also identified the temporal cortex as a region in dog brains where facial recognition takes place.

Berns' study showed that this activity occurs in response to both human and canine faces. The current study applied a bit more magnification, showing that human faces elicit activity in the caudate nucleus, a region associated with reward. On a neurological level, this could indicate that the relationships dogs have with humans are even more satisfying than the relationships they form with members of their own species.

Source: Cuaya LV, Hernández-Pérez R, Concha L (2016) Our Faces in the Dog's Brain: Functional Imaging Reveals Temporal Cortex Activation during Perception of Human Faces. PLoS ONE 11(3): e0149431. doi:10.1371/journal.pone.0149431