What a Dog’s Tail Can Reveal About Its Brain


Sometimes, scientists investigate weird things that might seem unimportant or irrelevant to a lot of people. There was that whole fuss last year about government funding for studies about duck genitals, for instance. There probably aren’t any kids in science classrooms thinking to themselves, “When I grow up, I want to study the reproductive organs of birds!” If we learned anything from that study (anything not related to duck genitals, at least), it’s that if a research project is strong enough to be funded by our tax dollars, you can bet that there’s something important to be learned from it.

Such is the case with a study I recently came across about the messages dogs are sending to each other with their tails. A group of researchers in Italy outfitted dogs with special vests that could measure their heart rates. Then, they showed the dogs videos of other dogs wagging their tails (a few of the videos were of real dogs, but most were digitally created silhouettes of real dogs). Importantly, sometimes the videos showed dogs wagging their tails to the right side of their bodies, and sometimes the videos showed dogs wagging their tails to the left side of their bodies.

The researchers found that dogs didn’t really react when they saw a dog wagging its tail to its right side - they calmly watched the dog on the screen wagging away. However, when they saw a dog wagging its tail to its left side, their heart rates jumped, and they became visibly more agitated. So in a nutshell, dogs are sensitive to the direction of tail wagging: right wags seem to be interpreted as no big deal, but left wags seem to be taken as aggression.

If you’re a dog person (like me), you might think this is a pretty interesting report on its own, but if you’re not into dogs, then you probably don’t really care about their wagging tails. Well, dog-haters, take heart: the reviewers for the journal Current Biology would not have accepted this paper for publication if there wasn’t a grander point.

Previous research has shown that dogs process emotions primarily with the right side of their brains. Coincidentally, dogs also use the right side of their brains to control left-sided movements, like tail-wagging. This paper builds upon both of those points, by showing that these kinds of asymmetries in the brain can actually affect their actions. We see this pretty clearly in people, but this is some of the clearest evidence yet that it shows up in evolutionarily “simpler” animals, and can help us understand how our own brain asymmetries can lead to differences in behavior.

Make sense? You see, studies like this one have to make a broader point than “left wags are bad,” else they wouldn’t get any funding, and they certainly wouldn’t make it into a reputable journal (maybe a reputable veterinary journal, but that’s not really the kind of stuff we discuss here). That said, I personally find the implications of this research for dog-owners to be more interesting than the implications for brain scientists. So the next time you meet a dog, make sure you pay attention to its tail - it could be the difference between a friendly encounter and a furry disaster!




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