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Wagging School

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Professor Giorgio Vallortigara, from Trento University’s Centre for Mind/Brain Sciences, explores brain lateralisation and how this manifests itself when dogs wag their tails. The brain is made of two hemispheres (the right and the left) and they perform different functions. Such functions are usually studied looking at paired organs, like right and left eyes, right and left hands or right and left ears.
Some years ago Professor Vallortigara became interested in medial, unpaired organs like the tongue or the tail, and whether there was competition or cooperation between the two hemispheres. Professor Vallortigara reasoned that tail wagging in dogs might be a good candidate for investigation because dogs move their tails as a response to emotional stimuli.
A very simple experiment was set up in which dogs looked at different types of stimuli eliciting likely emotional responses. They looked at their owners or other familiar persons, to a cat or to another quite aggressive dog. The movement of the tail to the right or the left was measured and frame by frame analysis was used to determine the amplitude of each sequence of movements. One would expect such movements to the right or left would be symmetrical.

Tail wag with owner and then unfamiliar dog        Play  Tail video2.wmv  
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The movement of the tails depended on the contralateral side of the brain. The neuron fibres from the brain cross over in the spinal cord, so that movement of the tail to the right is controlled by the left side of the brain and movement of the tail to the left is controlled by the right side.
When dogs looked at their owners there was large amplitude of tail wagging to the right. When the dogs looked at another person, this amplitude was less but it was still to the right and when they looked at a cat there was a very pronounced reduction in this right-side biased amplitude. When they looked at a dominant dog, however, they showed a left bias in tail wagging, indicating higher activation of the right hemisphere of the brain.
Most stimuli operate in a dichotomy, a good stimulus producing an approach response and a bad stimulus producing a withdrawal response. Approach responses are associated with high activity in the left hemisphere of the brain and withdrawal responses are associated with activity in the right hemisphere. Because stimuli producing approach responses were activating more the left side of the brain, the subsequent tail wagging was to the right. Stimuli producing withdrawal responses (activating the right side of the brain) led to tail wagging to the left.
Such responses are not unique to dogs. In humans, for instance, there is lateralisation for emotional function where the left hemisphere is involved in more positive emotion and the right is involved in more negative emotion. It remains open as to whether this brain asymmetry also has a functional or communicative role. Is such behaviour important in animals especially when they interact with each other?


Below: Visual stimuli (naturalistic and silhouette) showed predominantly left- or right-asymmetric tail wagging. In this set of stationary stimuli not wagging their tail are also showed. The still pictures are single frames from the moving videos.


In another experiment dogs were shown movies of other dogs. These movies were manipulated to show prevalent right-side tail wagging or prevalent left-side tail wagging or no wagging at all. The movies used realistic images of other dogs or silhouettes in order to see the effect of the tail wagging without any other stimulus.
This time both behaviour and physiological responses (heart rate) were measured. When observing dogs saw other dogs their tails wagged to the left, they exhibited more stress, anxiety and alert behaviour. There was also an increase in cardiac activity. When observing dogs saw right tail wagging they exhibited more relaxed and neutral behaviour with no increase in cardiac activity. This fitted in well with previous results which showed a bias for tail wagging to the right associated with an approach response. The dogs were communicating an emotional effect to the observing dogs. When dogs are in an extremely fearful condition there would be very strong activation of the right hemisphere.

Visual stimuli (naturalistic and silhouette) showed predominantly left- or right-asymmetric tail wagging. In this set of stationary stimuli not wagging their tail are also showed. The still pictures are single frames from the moving videos. In this study both behavioural responses and heart rate were measured. The results are presented graphically in the image below.    

Neuroscientists like Professor Lesley Rogers have argued that hyper activation or an excess of activity of the right hemisphere could be associated with pathological conditions in animals. Behavioural tests that look at lateralisation of function could be used to alleviate the conditions of such behavioural stress. Indeed, dog owners could be trained in the use of such simple tests. All of this research suggests that “wagging school” may be helpful for dogs. 

Professor Giorgio Vallortigara was interviewed for A Question of Balance by Ruby Vincent. All images from Professor Vallortigara. Summary text by Victor Barry, August 2016  

Did You Know? There is a famous cartoon showing schematic faces. The faces are similar, the only difference being the mouth and eyebrow are moving up either to the right or to the left. Most people identified a happy face with the face that showed the mouth up to the left. When people look at faces of other humans there is a tendency to pay attention to their left side which conveys a positive emotion. Such a bias tendency could be similar in dogs.    

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