Smile! Your dog’s brain will light up in response By Virginia MorellMar. 27, 2018 , 4:45 PM iStock.cpm/Antonio_Diaz As every dog lover—and scientist—knows, man’s best friend is good at reading faces. Dogs can tell the difference between happy and not-so-happy expressions, such as anger and sadness. Like us, they watch the left sides of peoples’ faces—where emotional cues first appear. And they even seem to be able to interpret our emotions and modulate their behavior accordingly. But what are the neural mechanisms that control how dogs process human faces?To find out, scientists trained eight dogs—mostly border collies—to lie still in a functional magnetic resonance imaging scanner while viewing photos of strangers with either happy or neutral expressions. The faces matched the gender of the dogs’ chief caretakers, because dogs have been shown to score lower on tasks involving faces of the opposite sex. The results: A happy human face produces a distinctive signature in a dog’s temporal lobe and other neural regions, the scientists report online this week on the preprint server bioRxiv.In a follow-up experiment, the pooches’ brains were scanned as they looked at faces expressing happiness, anger, fear, or sadness. The happiness pattern was so distinctive that a machine learning program could pick it out from brain activity linked to all the other emotions. (A similar “happiness” signature is found in humans.) That means, the researchers say, that our human emotions are represented in our pooches’ brains—which suggests that our canine pals really do know what we’re feeling.