Pet owners have always known that dogs that wag their tails are typically happy and dogs that don't tend to be sad.
But now researchers say it's not just the wag — but how they wag — that indicates their state of mental being.
When dogs feel positive about something, an Italy-based research team contended in their study published in the March 20 issue of Current Biology, they wag their tails to the right side of their rear ends. When they have negative feelings, their tails lean left.
The study, which was reported by the New York Times, was conducted by 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," Richard J. Davidson, director of the Laboratory for Affective Neuroscience at the University of Wisconsin in Madison, told the Times. The study's results complement what is already known about emotional asymmetry in the brain, he said.
The left side of the brain in animals and humans, which controls the right side of the body, is known from past studies to control what scientists call "approach and energy enrichment," or feelings of love, safety and calm. The right side of the brain, which controls the left side of the body, tends to be associated with feelings of fear and depression.
However, because dog's tails are centered in their body, researchers hoped to find out if they reflected either the positive or negative emotions associated with the left and right side of the brain.
To find out, Vallortigara's team used 30 family pets of various breeds that were being enrolled in an agility training program, the Times reported.
The dogs were placed in a cage equipped with cameras that precisely tracked the angles of their tail wags, according to the Times. Then they were shown four stimuli through a slat in the front of the cage: their owner, an unfamiliar human, a cat and an unfamiliar, dominant dog.
In each instance the test dog saw a person or animal for one minute, rested for 90 seconds and saw another view. Testing lasted 25 days with 10 sessions per day, the Times reported.