See
http://www.nytimes.com/2007/04/24/science/24wag.html?_r=2&ref=science&oref=slogin&oref=slogin
For diagram and video

April 24, 2007
If You Want to Know if Spot Loves You So, It¹s in His Tail

By SANDRA BLAKESLEE
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 ³don¹t mess with me.² Ears perked up, wriggly body and vigorously
wagging tail means ³I am sooo happy to see you!²

But there is another, newly discovered, feature of dog body language that
may surprise attentive pet owners and experts in canine behavior. 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, ³Asymmetric tail-wagging responses by
dogs to different emotive stimuli,² 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.

³This is an intriguing observation,² 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 specializes in behaviors 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 specializes in behaviors involving
withdrawal and energy expenditure. In humans, these behaviors, 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, Dr. Davidson said, because they are in the
midline of the dog¹s body, neither left nor right. So do they show emotional
asymmetry, or not?

To find out, Dr. Vallortigara and his colleagues recruited 30 family pets of
mixed breed that were enrolled in an agility training program. The dogs were
placed in a cage equipped with cameras that precisely tracked the angles of
their tail wags. 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.

When the dogs saw their owners, their tails all wagged vigorously with a
bias to the right side of their bodies, Dr. Vallortigara said. Their tails
wagged moderately, again more to the right, when faced with an unfamiliar
human. Looking at the cat, a four-year-old male whose owners volunteered him
for the experiment, the dogs¹ tails again wagged more to the right but in a
lower amplitude.

When the dogs looked at an aggressive, unfamiliar dog ‹ a large Belgian
shepherd Malinois ‹ their tails all wagged with a bias to the left side of
their bodies.

Thus when dogs were attracted to something, including a benign, approachable
cat, their tails wagged right, and when they were fearful, their tails went
left, Dr. Vallortigara said. It suggests that the muscles in the right side
of the tail reflect positive emotions while the muscles in the left side
express negative ones.

While some researchers have argued that only humans show brain asymmetry ‹
based on the evolution of language in the left brain ‹ strong left and right
biases are showing up in the brains of many so-called simpler creatures,
said Lesley Rogers, a neuroscientist who studies brain asymmetry at the
University of New England in Armidale, Australia.

Honeybees learn better when using their right antenna, she said. Male
chameleons show more aggression, reflected as changes in body color, when
they look at another chameleon with their left eye. A toad is more likely to
jump away when a predator is introduced to its left visual field (right
brain/fear). The same toad prefers to flick its tongue to the right side
when lashing out at a cricket (left brain/ nourishment) .

Chicks prefer to use their left eye to search for food and right eye to
watch for predators overhead, Dr. Rogers said. But when chicks are raised in
the dark, they do not develop normal brain asymmetry. In trying to eat and
watch for hawks overhead, such nonlateralized chicks become confused and
vulnerable to attack.

Sheep, which are good at recognizing individual faces, use the right sides
of their brains for knowing a Dolly from a Molly.

Chimpanzee brains are asymmetrical in the same ways as human brains, said
William D. Hopkins, a researcher at the Yerkes National Primate Center and
psychologist at Agnes Scott College in Atlanta. When chimps are excited,
they tend to scratch themselves on the left side of their bodies, reflecting
strong negative emotions, he said. And left-handed chimps are more fearful
of novel stimuli than right-handers. Their dominant right brains may make
them more cautious.

Brain asymmetry for approach and withdrawal seems to be an ancient trait,
Dr. Rogers said. Thus it must confer some sort of survival advantage on
organisms.

Animals that can do two important things at the same time, like eat and
watch for predators, would be better off, she said. And animals with two
brain hemispheres could avoid duplication of function, making maximal use of
neural tissue.

The asymmetry may also Adminse from how major nerves in the body connect up to
the brain, said Arthur D. Craig, a neuroanatomist at the Barrow Neurological
Institute in Phoenix. Nerves that carry information from the skin, heart,
liver, lungs and other internal organs are inherently asymmetrical, he said.
Thus information from the body that prompts an animal to slow down, eat,
relax and restore itself is biased toward the left brain. Information from
the body that tells an animal to run, fight, breathe faster and look out for
danger is biased toward the right brain.

In this way, Dr. Craig said, animals are naturally designed to cope with
changing environments.

Copyright 2007 The New York Times Company