Our Faces in the Dog's Brain: Functional Imaging Reveals Temporal Cortex Activation during Perception of Human Faces

Abstract

Dogs have a rich social relationship with humans. One fundamental aspect of it is how dogs pay close attention to human faces in order to guide their behavior, for example, by recognizing their owner and his/her emotional state using visual cues. It is well known that humans have specific brain regions for the processing of other human faces, yet it is unclear how dogs’ brains process human faces. For this reason, our study focuses on describing the brain correlates of perception of human faces in dogs using functional magnetic resonance imaging (fMRI). We trained seven domestic dogs to remain awake, still and unrestrained inside an MRI scanner. We used a visual stimulation paradigm with block design to compare activity elicited by human faces against everyday objects. Brain activity related to the perception of faces changed significantly in several brain regions, but mainly in the bilateral temporal cortex. The opposite contrast (i.e., everyday objects against human faces) showed no significant brain activity change. The temporal cortex is part of the ventral visual pathway, and our results are consistent with reports in other species like primates and sheep, that suggest a high degree of evolutionary conservation of this pathway for face processing. This study introduces the temporal cortex as candidate to process human faces, a pillar of social cognition in dogs.

Decoding Human Emotional Faces in the Dog’s Brain

“…We found cerebral activity related to the processing of happy faces in the right hemisphere, mainly in the temporal cortex. Previous studies found that the perception of human faces (vs. objects) elicits a strong response in the ventral temporal cortex 10,11 , and our current study extends said findings, showing that the strongest response to happy faces is located in the superior portion of the temporal lobe. Both results are remarkably similar to reports with humans 12,13 .…”

“…Other fMRI studies with dogs have also shown activation of this structure because it has been related to reward 29 and to familiarity of scents 30 . Our group also found greater caudate activity related to neutral human faces than to objects 10 . Considering that all stimuli used were unfamiliar to dogs, we suggest that the caudate activity reflects that a happy human face is intrinsically processed as a reward.…”

“…Those dogs did not require additional training. The new participant (Molly) was trained using the same procedure as the other seven dogs 10 .…”

“…Each image was presented only once during each run to avoid habituation to the images. In order to have closer natural stimuli, all images were in color, presented in a frontal view, and the size of the projected images was similar to that of a real face (15 cm x 20 cm), as this size has been used in other studies 2,10,42 . The gender of the faces presented to each participant was the same as the main caretaker: four dogs (one male dog and three female dogs) saw female faces and the other four participants saw male faces.…”

Awake canine fMRI predicts dogs’ preference for praisevsfood

“…These findings are consistent with social attachment accounts of the dog–human bond (Topál et al , 1998; Palmer and Custance, 2008; Nagasawa et al , 2015) and could provide a proximal neural mechanism supporting that attachment: reward-related activity in the ventral striatum. Of note, prior association of owner with food could drive caudate response to praise, and evidence suggests that even just viewing an unfamiliar human face may activate ventral striatum in dogs (Cuaya et al , 2016). Clearly, there are multiple avenues by which humans may come to be rewarding to dogs.…”