Is your dog happy or stressed? The answer is all in the wag. Italian researchers recently unveiled how the movements of a dog’s tail reflect their mood, and how other dogs can pick up these emotional cues.
We know in humans that positive and negative emotions are regulated by the left or right hemispheres of the brain, respectively. In addition, the right side of the brain is responsible for left-handed movements, while the left side is responsible for right-handed movements. This is known as brain asymmetry.
Just as in humans, in dogs the two sides of the brain also play different roles in emotions and movements. The most obvious differences involve paired organs – ears and eyes, for example – but how does this brain asymmetry affect single organs, such as a tail?
Dog Wags: Right Means Happy, Left Means Stressed
Studies back in 2007, led by neuroscientist Prof Giorgio Vallortigara, based at the University of Trento in Italy, identified that happy and relaxed dogs tend to wag their tail to the right (from the dog’s point of view), while stressed or anxious dogs have a more left-handed tail swing.
“We presented dogs with stimulus evoking different types of emotional responses – the owner, a cat, or an aggressive dog – and measured the relative amplitude of tail wagging movements to the left and to the right,” Prof Vallortigara explained Decoded Science. “What we found was that a positive response was associated with a bias in tail wagging to the right and negative response with a bias in tail wagging to the left.”
In the new study, published in the journal Current Biology, the same team tested whether other dogs can recognise and react to these subtle differences. In 43 dogs of different breeds, they measured heart rates and observed behaviour as the animals watched videos of dogs waging their tails to the left or to the right. The animals were presented with either a natural version or a digitised silhouette of other dogs.
The results were striking: When dogs watched another canines move their tail to the right – showing a left-hemisphere activation – they remained friendly and relaxed, maintaining a low cardiac frequency. However, when the dog on film was wagging its tail to the left – showing right-hemisphere activation – their heart rates increased and the animals appeared anxious and stressed, explained Prof Vallortigara.
Dog Communication via Tail Wag?
Prof Vallortigara doesn’t believe that tail wag-direction is something dogs can control and use to communicate intentionally with each other. Asymmetric tail wagging occurs as a result of activation of the left or right side of the brain when dogs look at different emotional stimulus, he explained. “They do not intend to communicate anything, it’s simply something that happens.”
The interesting aspect is that such a left- or right-biased tail wagging seems to have a meaning between two dogs watching each other. “Again, it is unlikely that this involves any explicit ‘understanding’ by the observer dog,” added Prof Vallortigara. “It may be that dogs learn by repeated encounters with other dogs to associate left or right tail wagging with different behavioural responses.”
Prof Vallortigara’s favourite explanation, however, is that tail wagging to the right, for example, is detected first by the left hemisphere, predisposing both the wagging and the observing dog to a positive emotional response.
Click to Read Page Two: Tail Wagging Research