A dog wagging its tail (Bill McChesney via Creative Commons @ Flickr)

(Bill McChesney via Creative Commons @ Flickr)

The direction in which a dog wags its tail can communicate its emotional state to other canines, according to a new study published in Current Biology.

The Italian research team behind the study says dogs recognize, and respond accordingly, whether other canines wag their tails to the right or to the left.

The reason dogs understand the right versus left tail wag, according to the researchers, is because they have asymmetrically organized brains, meaning that the left and right sides of our brains are each responsible for controlling different things, much like humans.

In an earlier study, the researchers found dogs tend to wag their tails to the right when they feel positive, such as when they see their owners. Dogs wag their tails to the left when they experience negative emotions, such as feelings that might be triggered by an unfriendly dog or some other kind of danger.

The researchers say that this left and right tail wagging behavior is because of what’s taking place in the canine’s brains. A wag to the right is brought on by activation on the left side of its brain, while activity in the right side of the brain produces a wag to the left.

While this right versus left wagging behavior means something to other dogs, the researchers say that they’re probably not purposely displaying this behavior to communicate with each other.  Instead they say it’s just an automatic response due to left side or right side brain activation. But the team also points out that this behavior could serve a very helpful purpose to people like dog owners and veterinarians as another way to better understand what’s going on with the animal.

Compilation of videos shown to test dogs – left, right, no tail wagging – (Current Biology, Siniscalchi et al.)

To make their findings the researchers showed their dog subjects videos of other dogs either wagging their tails to the left or right. When the test dogs saw a video of a dog wagging its tail to the left, their heart rates increased and they appeared a bit nervous. However, when the dogs saw another animal wagging its tail to the right, they remained calm.

“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. That is amazing, I think.”