Pooches produce happy tears in response to their favourite humans, adding a new dimension to an age-old story of love and companionship.
A Japanese study is the first to show positive emotions can stimulate tears in animals other than humans, namely man’s best friend.
Researchers carefully measured the tear volumes of 18 dogs under three scenarios.
The first set the baseline for the study – normal tear volumes when the dogs were chilling at home with their owners.
The second measured tear volumes within the first few minutes of the dogs reuniting with their owners after time apart, and the third measured tear volumes after reunions with people they knew but who weren’t their owners.
“We found that dogs shed tears associated with positive emotions,” said Takefumi Kikusui of Azabu University, adding that the results were unequivocal.
Tear volumes increased significantly during owner reunions, and more tears were produced during owner reunions than those involving familiar, non-owners.
Suffice to say dog tears are different to human ones. They are the welling-up kind, not the streaming-down-the-face kind.
But the study suggests the same neurochemical, oxytocin, is associated with crying in both species.
It’s often referred to as the attachment hormone and humans produce lots of it in certain situations such as mother-baby bonding, and intimate time with loved sexual partners.
Another part of the study saw researchers administer oxytocin droplets, or a placebo, into the eyes of 22 dogs. The result was an increase in tear volume, suggesting oxytocin might mediate tear secretion during owner-dog reunions.
The final part of the study focused on human responses to the phenomena of doggy tears.
Participants were shown a range of photos of dogs with or without artificial tears and asked to rate how compelled they felt to care for them.
The dogs with wet, teary looking eyes ranked significantly higher than shots of tearless dogs.
The findings suggest that tear production in dogs helps them form stronger connections with their humans.
La Trobe University dog researcher Tiffani Howell is fascinated by the findings. She says other research has shown oxytocin levels also rise in humans when they are with their dogs.
“We want to be together because we like being together, because it makes us feel good to be together. That clearly seems to be the case for both parties,” said Dr Howell, who was not involved in the study.
“Humans love being with their dogs, and dogs love being with their owners. They want that sort of closeness and probably the oxytocin is part of that.”
The study has been published in the journal Current Biology.
(Australian Associated Press)