Italian researchers found that dogs recognise and respond differently when their fellow canines wag to the right than they do when they wag to the left.
The same team earlier found that dogs wag to the right when they feel positive emotions (upon seeing their owners, for instance) and to the left when they feel negative emotions (upon seeing an unfriendly dog, for example).
That biased tail-wagging behaviour reflects what is happening in the dogs’ brains. Left-brain activation produces a wag to the right, and right-brain activation produces a wag to the left.
The new study found that tail-wagging difference means something to other dogs too. While monitoring their reactions, the researchers showed dogs videos of other dogs with either left- or right-asymmetric tail wagging.
When dogs saw another dog wagging to the left, their heart rates picked up and they began to look anxious. When dogs saw another dog wagging to the right, they stayed perfectly relaxed.
“The direction of tail wagging does in fact matter, and it matters in a way that matches hemispheric activation,” said Giorgio Vallortigara of the Center for Mind/Brain Sciences of the University of Trento.
“In other words, a dog looking to a dog wagging with a bias to the right side¿and thus showing left-hemisphere activation as if it was experiencing some sort of positive/approach response would also produce relaxed responses.
“In contrast, a dog looking to a dog wagging with a bias to the left and thus showing right-hemisphere activation as if it was experiencing some sort of negative/withdrawal response would also produce anxious and targeting responses as well as increased cardiac frequency,” Vallortigara said.
Vallortigara doesn’t think that the dogs are necessarily intending to communicate those emotions to other dogs. Rather, he said, the bias in tail wagging is likely the automatic byproduct of differential activation of the left versus the right side of the brain. The findings were published in the Cell Press journal Current Biology.