Does a dog’s wagging tale tell us how he’s feeling? Scientists think they may have unlocked a key to the emotional communication of a dog’s wagging tail.
Most of us know that a wagging tail expresses not only happiness but a host of emotions. In 2007, Italian researchers reported that a wag to the left indicates negative emotions; while a wag to the right indicates positive ones.
That is, happy dogs wag their tails more to the right (from the dog’s point of view), while nervous dogs have a left-dominated swish.
Now the same team of scientists has found that other dogs may know best what this means. In fact, scientists now believe that fellow canines can spot and respond to these subtle tail differences.
In a recent study reported in the journal Current Biology, researchers presented videos to dogs showing other dogs wagging their tails. When the dogs watched a tail wag to the left, the dogs showed signs of anxiety, expressed in physical changes such as a higher heart rate. But when the video showed the tail going in the opposite direction, the observing dogs remained calm.
This suggests that dogs, like humans, have asymmetrically organized brains, according to neuroscientist, Giorgio Vallortigara, at the University of Trento, an author of the study. “The emotions are associated presumably with activation of either the right or left side of brain,” he said.
Just as in humans, for dogs the right side of the brain is responsible for left-handed movement and vice versa, and the two hemispheres play different roles in emotions.
“It is very well known in humans that the left and right side of the brain are differently involved in stimuli that invokes positive or negative emotions,” said Professor Vallortigara. In other words, left-brain activation produces a wag to the right; right-brain activation produces a wag to the left.
Nevertheless, Dr. Vallortigara is hesitant to confirm that dogs are wagging their tails to communicate with one another. “This is something that could be explained in quite a mechanistic way,” he said. “It’s simply a byproduct of the asymmetry of the brain,” and dogs learn to recognize the pattern over time.
This was not the first study to examine whether left and right were important to canines.
Last year a team from the University of Lincoln found that dogs turn their heads to the left when looking at an aggressive dog and to the right when looking at a happy dog.
But, in another research paper from the University of Victoria in Canada: “Dogs were more likely to approach a robot dog when its ‘tail’ was made to wag left rather than right, rather than becoming anxious – the opposite way around to the [Italian] study.”
Dog behavior expert John Bradshaw, a visiting fellow at the University of Bristol’s school of veterinary science, said: “the differences could be because the dogs in the different studies were not fully interpreting the animals in the films or robo-dogs as canines. A study of how dogs responded to real dogs could help.”
“While there is considerable evidence from many different mammals that the two sides of the brain are used for different purposes, much of the detail still has to be hammered out – and dogs are no exception,” he said.
“However, given the ease with which their behavior can be recorded, it will probably not be long before we understand why dogs wag their tails sometimes one way, sometimes the other.”
A version of this article appears in print as: “A Dog’s Tail Wag Says a Lot, to Other Dogs.” [New York Times, November 5, 2013, p. D4]
A special wag to Ronnie Londner for finding and sending me the articles about the research into the meaning of dog tails. (But should I be wagging to the right or the left? I’m so confused…)