Answer:
The area in the brain of the dog that gets triggered when looking at other dogs faces and expressions is also triggered when looking at human faces.
There is also an area in the human brain that gets triggered when looking at other human faces. This area of the brain is located at the bottom part of the cortex, which is back behind your ears, if I remember correctly!
Scientists know that other animals have cells in their brain not unlike the cells humans have for recognizing human faces, except its for recognizing members of their species (Like a dolphin knowing that they are looking at another dolphin), but then they started to ask if animals (more specifically dogs) had the same / similar cells humans do (so that they know human faces and expressions)
To test this, they did a fMRI, which is not easy for a dog to do. Confined spaces and loud noises are enough to make anyone twitch, think about those conditions for a dog! They have to ignore all of them and lay motionless, and I don't know about other peoples dogs but if another dog in the neighborhood barks, it arouses my dog from a deep sleep and sets her off!
Anyways... The dogs (They used seven to test this) had to go through extensive training. Meaning it could be months before they actually got to test to see if dogs could recognize human faces.
Now to the part you actually asked about:
During the test, the dogs were shown pictures of neutral human faces with common objects and they showed little activity, BUT when the pictures were shown to the dogs, the researches saw that the top part of the cortex was active when shown human faces, but not anything else.
Meaning, dogs respond to human faces in the same area of the brain that they respond to other dogs.
I had fun looking this up and found a lot of interesting information, so I hope this isn't to long for you >.<
There are a lot of interesting websites on this and if you have the time to look this up yourself and read them, I suggest you do!
Explanation: