With more than two decades as a professional dog trainer and educator, Penny Layne has seen her share of wagging tails. But she has never determined a canine's demeanor by whether its tail flicked to the left or right.
Dogs, however, cue in to such tail-wagging signals, according to a team of Italian researchers who have expanded upon their 2007 study that dogs wag to their right side when feeling positive emotions and to their left side when feeling negatively.
The researchers, whose latest study was published Thursday in the journal Current Biology, showed that dogs, like humans, have asymmetrically organized brains, with the left and right sides playing different roles. A dog feeling a positive emotion, such as when seeing its owner, would process that in the left side of its brain, producing a tail wag to its right. Conversely, a dog feeling a negative emotion, such as seeing an unfriendly dog, would process that in the brain's right side, producing a left-side wag.
In their research, the investigators monitored the reaction of dogs watching videos of other dogs wagging their tails. When the dogs saw another dog wagging to the left, their heart rates picked up and they began to look anxious. When dogs saw another dog wagging to the right, they remained relaxed.
Simply put, a dog wagging with a right-side bias -- indicating a positive/approach response -- would produce relaxed responses in other dogs viewing that. And a dog wagging with a bias to the left -- as it experiences some sort of negative/withdrawal response -- also would produce an anxious response in a dog viewing the tail wagging, said one of the researchers, Giorgio Vallortigara, professor of neuroscience and director of the Center for Mind/Brain Sciences of the University of Trento.
But Ms. Layne and other local pet experts who hadn't seen the study said they were unsure what it was attempting to show.
"I've never heard of the left or right wagging [theory]," said Lawrence Gerson, a veterinarian and founder of the Point Breeze Veterinary Clinic who writes a biweekly column for the Pittsburgh Post-Gazette.
"Dogs do communicate with their tails, certainly, but I don't know whether you can perceive whether they are wagging to the left or the right.
"Dogs wag their tails like windshield wipers," he said.
Mr. Vallortigara conceded that most dogs wag their tails back and forth, "but given that we are interested in the left/right asymmetry of the brain, we looked only for these sort of left/right biases in tail wagging.
"They do not intend to communicate anything with such an asymmetric tail wagging," said Mr. Vallortigara, who holds a doctorate in cognitive neuroscience, indicating it's just intuitive to the dogs. "It is simply something that happens. The interesting thing is that such an asymmetric tail wagging seems, however, to have meaning for a dog looking at tail wagging of another [dog]."
Bias in wagging and its response might find practical uses among veterinarians, dog owners and dog trainers, he added.
"I can imagine they can be exploited, for instance, by selecting a direction of approach to dogs during veterinary visits or in general when approaching a novel dog. Also, I can imagine ... use of asymmetrical tail wagging to favor a different type of learning during agility or obedience teaching promoting friendly or aggressive behaviors."
Ms. Layne was familiar with the theory about wagging to the right or the left but said there are so many other visible cues about what a dog is feeling that it doesn't make sense to her to focus solely on the tail.
"I don't dispute the research, but what I have is the experience of the last 22 years of studying dogs and training them and as a speaker and I'm reading more than just the tail.
"You really have to look for a while to see if the tail is going left or right. You can't waste that much time if your life is threatened. And dogs can't take that much time to determine if another dog is friendly or not friendly."
There are easy-to-read "telltail" signs of aggression or relaxation, she said. A tail sticking straight up in the air is a dog at full arousal, she said. One whose tail -- and entire body -- is limp is in a relaxed state.
There are other body language clues, she said. A direct stare with large pupils and stiff ears and a stiff body leaning forward with a clenched mouth are signs of arousal. Conversely, a dog whose body is loose and doesn't line up is a relaxed animal.
She said the issue of right or left wagging occasionally comes up, as it did recently at a dog safety course she conducted for a company whose employees measure surface vibration in the backyards of homes near Marcellus Shale drilling sites.
"They wanted to know if there was any truth to the left or right tail wagging theory," she said. "I told them, 'I can tell you a dog wagging its tail in a full circle is a very happy dog.' "
Michael A. Fuoco: email@example.com or 412-263-1968. First Published October 31, 2013 1:09 PM