which way does it wag?

New York, April 25: Every dog lover knows how a pooch expresses its feelings.

Ears close to the head, tense posture, and tail straight out from the body means “don’t mess with me.” Ears perked up, wriggly body and vigorously wagging tail means “I am sooo happy to see you!”

But there is another, newly discovered, feature of dog body language that may surprise attentive pet owners and experts in canine behaviour.

When dogs feel fundamentally positive about something or someone, their tails wag more to the right side of their rumps. When they have negative feelings, their tail wagging is biased to the left.

A study describing the phenomenon, “Asymmetric tail-wagging responses by dogs to different emotive stimuli,” appeared in the March 20 issue of Current Biology. The authors are Giorgio Vallortigara, a neuroscientist at the University of Trieste in Italy, and two veterinarians, Angelo Quaranta and Marcello Siniscalchi, at the University of Bari, also in Italy.

“This is an intriguing observation,” said Richard J. Davidson, director of the Laboratory for Affective Neuroscience at the University of Wisconsin in Madison. It fits with a large body of research showing emotional asymmetry in the brain, he said.

Research has shown that in most animals, including birds, fish and frogs, the left brain specialises in behaviours involving what the scientists call approach and energy enrichment. In humans, that means the left brain is associated with positive feelings, like love, a sense of attachment, a feeling of safety and calm. It is also associated with physiological markers, like a slow heart rate.

At a fundamental level, the right brain specialises in behaviours involving withdrawal and energy expenditure. In humans, these behaviours, like fleeing, are associated with feelings like fear and depression. Physiological signals include a rapid heart rate and the shutdown of the digestive system.

Because the left brain controls the right side of the body and the right brain controls the left side of the body, such asymmetries are usually manifest in opposite sides of the body. Thus many birds seek food with their right eye (left brain/nourishment) and watch for predators with their left eye (right brain/ danger).

In humans, the muscles on the right side of the face tend to reflect happiness (left brain) whereas muscles on the left side of the face reflect unhappiness (right brain).

Dog tails are interesting, Davidson said, because they are in the midline of the dog’s body, neither left nor right.

Vallortigara and his colleagues recruited 30 family pets of mixed breed that were enrolled in an agility training programme.

The dogs were then placed in a cage equipped with cameras that precisely tracked the angles of their tail wags.