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.

We usually think of smell as one of the five senses and a generally passive process. Odorants drift into our noses; receptors detect them and send signals to our brains. However, more so than vision or hearing, smell is an active process involving many groups of muscles. Animals can control the rate at which odors enter the nose by the way they sniff. Sniffing involves muscle movements in the face and the nose. It requires movements of the diaphragm to control the rate of air movement. And there is likely some control over the fine hairs inside the nose. This means that for smell in particular, we would also expect to see the involvement of parts of the brain that control movement.

If the scent of a dog activated the brain in the same pattern as the scent of a human, then that would tell us that dogs lumped us in the same category as them. If, on the other hand, dog and human scents caused different patterns of activation, then we would know that dogs have different categories for us and them.

Like the hot dog experiment, the dogs wouldn’t have to do anything except hold their heads still, and they were already pros at that. We would hold up cotton swabs in front of the dogs and let the scent drift into their noses. Later, we could analyze the fMRI data to see which parts of their brains reacted to different scents.

This experiment presented certain logistical complications. Where would we get the scents and how would we get them? These questions became the topic of heated debate in the lab, especially as it became apparent that everyone would have to give something for the cause.

“So let me get this straight,” Andrew said. “We are going to present scents from dogs and humans to Callie and McKenzie.”

“That’s right,” I said.

“What kind of scents?”

“Well,” I said, “we all know what dogs do when they greet each other.”

Andrew didn’t like where this was going. “You’re suggesting a butt wiping?”

“I don’t think there is any other way.”

Lisa chimed in and offered an alternative: “Dogs sweat from their paws. You could get scents from there.”

“But we would also pick up all sorts of smells from where the dogs walked,” I said. “Besides, dogs go right to the butt. As far as they’re concerned, that is where the good stuff is.”

“Are we talking about a butt wiping or something more substantial?” asked Andrew.

It was a good question. A swabbing of the perianal area would probably do the trick, but there was good evidence that urine would be a more powerful signal. Dogs can differentiate their own urine marks from those of other dogs, suggesting that dog urine contains unique pheromones that are the equivalent of doggie fingerprints.

“I think we need urine,” I said.

“What about the humans?” Andrew asked.

“If you’re doing it for the dogs,” Lisa said, “I think you should do it for the humans.”

Andrew and I looked at her aghast.

“What?” she said. “The first thing Sheriff does is stick his nose in someone’s crotch.”

Although Lisa had a point, there were some boundaries that we couldn’t cross. Besides, what she was suggesting could be construed as biohazardous waste by the university lawyers.