 Picture this: you’re riding in a car with a friend and she yawns. A few seconds later, you yawn too, even though you’re not tired or bored. Your friend yawns again and this time you decide you are going to resist yawning. But you can feel the darn yawn building in your throat until you just have to let it out! In fact, you might actually be stifling a yawn just from reading this! Congratulations – you’re human. Contagious yawning affects about 45 to 60% of healthy adult humans. It is thought to be associated with our capacity for empathy, so pat yourself on the back if you just yawned. When people yawn contagiously, neural networks responsible for empathy and social skills are activated.(1) In addition, people who score higher on self-recognition, theory of mind, and empathy are more susceptible to yawn contagiously.(2) Further, the contagious effect of yawning is impaired in subjects suffering from empathy disorders, such as autism.(3) Well, it turns out that dogs also yawn contagiously.
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 Remember the first time you had to give a presentation in public? You probably wrote down what you wanted to say, then read it out loud over and over, repeating the words just as you wanted to say them in the presentation. It was really, really boring, and you were thinking, “How often do I need to do this before it will stick in my head?”
Researchers at Johns Hopkins’ Department of Rehabilitation Medicine studying how people learn made an interesting discovery (1). They found out that the old adage, “perfect practice makes perfect,” was actually not quite true. Whether it’s memorizing a presentation or learning how to do a front cross in agility, it turns out that we learn faster if we don’t practice perfectly. Let me explain… How We Learn When we first begin to learn something, new neuronal pathways send messages to an area of the brain where they are stored. The more those pathways continue to deliver information to the memory storage area, the more permanent the memories become. Here’s an analogy. There is a huge parking lot on the south end of Baltimore with an elevated highway nearby. When you drive by that parking lot, you can see hundreds, if not thousands, of cars, all identical except for their different colors. These cars arrive by train and are offloaded and then parked in incredibly neat rows – row after row of the same make and model of car. As the train keeps delivering cars, the lot gradually gets full (Figure 1).  A dog using its dewclaws, preparing to “grip” the water. Photo by Tom Fretz. As a veterinary sports medicine specialist, I work extensively with canine athletes, developing rehabilitation programs for injured dogs or dogs that required surgery due to performance-related injuries. I have seen many dogs, especially field trial/hunt test and agility dogs, that have chronic carpal arthritis, frequently so severe that they must be retired or at least carefully managed for the rest of their careers. I noticed that very few of those dogs had dewclaws and began to wonder whether these appendages might, in fact, protect a dog from injuries. What I learned might surprise you.
The Anatomy of Dewclaws Miller's Guide to the Anatomy of the Dog, a veterinary anatomy text, has an excellent figure depicting the muscular anatomy of the distal forelimb. There are 2 functional muscles, the extensor pollicis longus et indicis proprius and flexor digitorum profundus, which are attached to the front dewclaw by 4 tendons (Figure 1). Each of those muscle/tendon units has a different function in movement. That means that if you cut off the dew claws, you are preventing the muscles that were attached to the dewclaws from functioning. In contrast, rear limb dewclaws do not have muscle/tendon attachments, so their removal might be appropriate, except in the breeds such as Briards and Beauceron in which they should be retained.  More specifically, dog eyes do and wolf eyes don’t. Let me explain.
Collaborators in the UK and US examined in detail the facial muscles, especially the muscles around the eyes, of dogs and wolves (1). It turns out that there are two prominent muscles that move the dog’s eyelids that many wolves don’t have, or if they do, they are vestigial – smaller and weaker. The first one, called the levator anguli oculi medialis or LAOM for short (why do we still use Latin names for muscles?) lifts the medial (the part of the eyebrows nearest the nose) part of the dog’s eyebrow up. Epic is using those muscles in the image above.  Oxytocin. Most of us think of it as the hormone that helps bitches whelp and produce milk. And yes, it’s that, but so much more. A series of recent studies have revealed how oxytocin has a major effect on the brains of both people and dogs to strengthen the human-canine bond – that indescribable interspecies attachment that might just explain why you’re reading this.
 What makes a dog a dog – that gregarious canine companion? People have been asking that for a very long time. Why is it that when you raise wolves with human care and companionship from the time they are born, while they are more comfortable around humans than wolves not raised with people, they never really become man’s/woman’s best friend?
This symbiotic relationship between dogs and humans began tens of thousands of years ago, with dogs getting room and board in exchange for light work such as vermin control. How did it morph into dogs becoming members of our extended families and part of our workforce? The answer to this question would help us better understand the nature of the human-canine bond and might hold the key to the process of domestication itself. |
AuthorCHRIS ZINK DVM PhD DACVP DACVSMR CCRT CVSMT CVA is one of the world’s top canine sports medicine and rehabilitation veterinarians. Archives
December 2019
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