What dogs' wagging tails tell others about themselves

Dogs recognize and respond differently when their fellow canines wag to the right than they do when they wag to the left, a new study has suggested.

The discovery follows earlier work by the same Italian research team, which 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 behavior 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.

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.

Giorgio Vallortigara of the Center for Mind/Brain Sciences of the University of Trento, said that the direction of tail wagging does in fact matter, and it matters in a way that matches hemispheric activation.

He said that 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.

Vallortigara asserted that 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.

The study has been published in the Cell Press journal Current Biology.