Dogs walk on their front legs.
But they also use their front legs to do other things. They dig. They jimmy open doors. They swipe food off the counter. And they hold toys and bones with their front paws. Maybe it wasn’t so far-fetched that when Callie and McKenzie were watching our hand signals that their brains were somehow simulating actions with their own paws. It would be a way for their brains to translate human action into equivalent dog action.
That would mean that when dogs watched us run, the neurons that controlled running in their brain would start to fire. It would mean that when we ate, their mouth neurons would be going haywire. I knew the absolute truth of this. How many times had I seen Callie licking her chops as I put a morsel of food in my mouth? It was as if she could almost taste it.
If dogs had mirror neurons that responded to human action, did humans have neurons that responded to dog action? Amazingly, yes. In 2010, an fMRI study reported that when people watched silent movies of a dog barking, the parts of the humans’ brains that responded to sounds were activated, even though there was no actual sound. It was like the humans filled in the sound of a dog barking just by observation.
But seeing this kind of mirror neuron activity in Callie and McKenzie meant that the whole dog-human relationship was not just a scam. If dogs had the ability to transform human actions into their own doggie equivalent, then maybe they really did feel what we feel. At least a dog version of it.
The caudate activity was proof that we could detect and interpret activity in the dogs’ brains. It showed that Callie and McKenzie understood the hand signals for something they liked—hot dogs. But the motor cortex activity suggested that they were more than Pavlovian learning machines. If, as we suspected, the cortex activity was because of mirror neuron activity, here was the first evidence that the dogs might be performing some kind of mentalizing. They were interpreting hand signals and possibly even mapping our hands onto their paws.
It was tantalizing evidence for dog theory of mind.
That evening, I was sitting on the sofa and Callie was doing her usual patrol of the house and yard. Kat and I had taken to leaving the kitchen screen door ajar, even though it let the mosquitoes in the house. It was easier than getting up and down to let Callie in and out. In the distance, I could hear coyotes howling, which normally sent Callie into a barking frenzy.
But not tonight.
After a few circuits of the yard, she came inside and hopped onto my lap. This was unusual because she was never really a lap dog. Mostly she would curl up with Lyra, apparently preferring the contact of her own kind. But tonight she nestled between my legs and laid her head on my thigh. And I was grateful for the dog-human contact.
I stroked her head gently. I loved the way her black fur slicked down on the flatness of her skull. Her eyes began to narrow as she drifted off to sleep.
Did she feel what I was feeling? She could have chosen anywhere in the house to sleep at that moment, but for whatever reason, she chose my lap. It wasn’t for food. It wasn’t for warmth—Lyra provided more heat than I could. It had to be that she wanted contact with a human. Me. The same desire I had for contact with a dog. Her.
Callie drifted off to sleep. Pretty soon I could feel her legs twitching as she started to dream. I pondered the possibilities of using fMRI to see what was happening in her brain while she dreamed.
My reverie was snapped by the thwack-thwack-thwack of her tail on the sofa. She was still dreaming.
Maybe she was dreaming of taking down one of those coyotes. Or maybe catching a tasty rodent in the yard. Or maybe it was just the dogness of being there, in my lap.
And if that wasn’t love, then I would surely accept it as a reasonable facsimile.
21
What’s That Smell?
THE RESULTS OF THE HOT DOG experiment made me wonder what the dogs thought of us humans. It seemed like there was more going on than just love of hot dogs. Each trip to the MRI, Callie got more and more excited. By the final scan session, she was making a beeline to the portable steps up to the patient table. She would shimmy into the scanner bore even before we had her chin rest in place. Her look said, I’m ready, let’s go! She liked interacting with all the people, and, as everyone agreed, she liked showing off. She had become a diva.
Callie had also gotten used to McKenzie. If I had to characterize their relationship, I would call it one of mutual nonthreatening coexistence. We used the lab as our staging area before walking everyone across the campus quad to the MRI facility. Callie and McKenzie would greet each other in the lab with a perfunctory butt sniff and tail wag. That would usually be it, as both dogs preferred checking out the humans in the room. Once at the scanner, though, Callie would start getting more excited. If it was McKenzie’s turn to go into the MRI, Callie would climb up on the patient table and try to get into the MRI before McKenzie. Callie would have to be carried off the table and kept in the control room while Melissa and McKenzie got situated.
I found this behavior fascinating. It seemed clear to me that the dogs treated each other differently from the way they treated us humans. This is despite the popular notion that we humans are a “pack” to the dogs—a sort of extended doglike family.
This gave me an idea for another fMRI experiment.
How do dogs categorize humans? Either dogs have separate categories for dogs and humans, or they lump us together as either pack or not pack.
To my eyes, Callie and Lyra behaved like pack mates. They ate together. They slept together. And they played together. It was no different from what we humans in the house did with them. And while we viewed them as family members, it would be nice to know if they viewed us that way too. Because Callie and Lyra were unrelated, and they were obviously unrelated to us humans, the notion of a pack would have to be what anthropologists call fictive kin.
Humans are particularly good at treating genetically unrelated friends as if they were family, especially if they go through an intense experience together. This is why soldiers call each other “brother.” If people do this, maybe dogs did too. If dogs viewed their humans as part of their pack—a sort of extended family—then dogs and humans should result in similar activation in the dogs’ brains.
So what might distinguish humans and dogs—at least in the dog’s mind? Apart from appearance, the most obvious is smell. After a dog sees another dog, it will make a visual assessment of body language, like how the tail is held, and decide whether to approach. If it does approach, then they will sniff each other. It is similar when dogs see humans. After a visual assessment, a dog will usually approach and scent the person.
A dog’s sense of smell is about one hundred thousand times as sensitive as that of a human. They also have an additional structure, a fluid-filled tube called the vomeronasal organ (VNO), thought to be specialized for detecting scents from other dogs and therefore to function in some capacity for social signaling.
With that powerful of a sense, you can be sure that a large portion of the dog’s brain is devoted to processing smells. Even so, I was still shocked when we got the first images of Callie’s and McKenzie’s brains. Where we would normally see a big frontal lobe in humans, the dogs had almost nothing. Instead, extending toward their snout, was a massive phallic protuberance—the olfactory bulb. A rocket in the socket. Humans have nothing like that. And it accounted for about 10 percent of the dog’s entire brain.