How Dogs Love Us: A Neuroscientist and His Adopted Dog Decode the Canine Brain (24 page)

“I have good news too,” Helen said.

“Really?”

Helen paused for dramatic effect.

“Come on,” Kat said. “Don’t keep us hanging.”

“I got an A on my science test.”

“Yay!”

“That’s awesome,” I said. “I’m very proud of you. You had to work really hard to do that.”

Helen beamed.

Sometimes playing hooky really does pay off.

20

Does My Dog Love Me?

T
HE FIRST PHASES OF THE
Dog Project were coming to an end. Callie had been to the scanner four times and McKenzie three. We had proved that the dogs could hold still enough to obtain high-quality images of their brains. And even more impressively, we had shown that the reward systems of their brains activated in response to the appropriate hand signals. We had finished the first scientific paper and sent it off for publication, which meant that we had some time to reflect on what we found and what we wanted to do next. As far as we knew, we had the only two dogs in the world trained to go into an MRI scanner, and we had proven that the whole crazy idea wasn’t so crazy after all.

The excitement in the lab was electrifying. I had been scanning human brains since fMRI was discovered, but nothing I had experienced in my career matched this intensity. Even the dawn of human brain imaging didn’t match. Perhaps because scientists had been studying the human brain in various ways for over a century, we already knew a lot about how it worked. More often than not, brain imaging tended to confirm what we knew about the human brain
and rarely resulted in a sea change in our understanding of the human mind.

But the Dog Project was entirely different.

I felt like Christopher Columbus discovering the New World. The dog’s brain was a great, unexplored continent. We had no idea how the canine brain worked, but we had the tools to figure it out and two subjects ready to assist. All we had to do was step into the unknown and start exploring.

The screensaver on Lisa’s computer was displaying a montage of Sheriff. Sheriff was almost two years old. Lisa had acquired him as a puppy when she graduated from Emory and started working in the lab. He was the first dog she could truly call her own, and she absolutely adored him.

“You really love Sheriff, don’t you?” I commented.

“Of course,” Lisa replied, “and he loves me too.”

Gavin, who had been observing with bemusement, couldn’t resist teasing Lisa about this.

“That depends on what you mean by love.”

Lisa, ever the pragmatist, replied, “Love? I would accept codependency.” She was dead serious. “Look, I think the best you can hope for with humans is to eventually have a relationship where both people are mutually dependent on each other. What’s wrong with that?”

She had caught Gavin uncharacteristically off guard and he had no response. Lisa continued. “So what if Sheriff’s love for me is based on food and belly rubs? He gives back affection and companionship. If most human relationships were that simple, more people would probably be happier.”

“What if we could prove that Sheriff loved you?” I asked.

“You mean more than food and belly rubs?”

Gavin rolled his eyes and said, “That’s impossible.”

Andrew, who had refrained from wading into the debate on love, had been staring intently at his computer screen. “Check this out.”

On the screen was the structural image of Callie’s brain. I had now seen this image a hundred times and knew it better than my own brain. Overlaid was an activation map. We had been looking at pictures like this for weeks and I had become accustomed to seeing the red, orange, and yellow hot spots superimposed on the caudate nucleus—the center of the reward system. But this image was different.

Andrew had digitally warped McKenzie’s brain to match Callie’s. This is a normal step in the analysis of human fMRI data. When we collect data on a large number of subjects, we need a way to compare activation in everyone’s brains. But because every person’s brain is physically different, we use a digital method that morphs each brain into the same size and shape. This allows scientists to average the activation patterns of many individuals and determine the commonalities of brain function.

In humans, brain sizes tend to vary by about only 1 or 2 percent. Some people have round heads while others are more oval-shaped. Even so, the basic anatomy is pretty much the same, and we need to stretch and twist the brains only a little bit to make them all match up.

Dogs are different. Of all the species on the planet, dogs have the largest variations in size. What other species can range in size from a 4-pound Chihuahua to a 150-pound Great Dane and still be considered the same animal? As you might expect, their brain sizes have a similarly large variation.

When we started analyzing the data from the Dog Project, we did it separately for Callie and McKenzie. McKenzie was about 50 percent larger than Callie, so we knew their brains were going to be
different. Because of this large variation in size, we didn’t think the usual computer algorithms would work, so we hadn’t even attempted to digitally combine their brains.

Until now.

By carefully identifying key landmarks in the dogs’ brains, Andrew had been able to get them to line up. Once aligned, he was able to perform an analysis on the combined dataset. They say that two heads are better than one, and in this case that was absolutely true. Although both Callie and McKenzie had performed beyond our expectations, they still had their limits. They had each stayed in the MRI for ten minutes of continuous scanning. But ultimately, the noise and confinement wore them down, and they got tired of the task. In the end, Callie had sat through almost forty repetitions of the task and McKenzie about thirty. This was good enough to prove the feasibility of canine fMRI. But to go to the next step, and really start figuring out how the dog brain worked, we needed a lot more repetitions and, ideally, a lot more dogs. Combining the results from Callie and McKenzie was a first step in this direction.

More observations meant more power to detect faint signals in the brain. By merging the datasets of the two dogs, we were now staring at a result on the computer screen that we hadn’t seen when looking at the dogs individually.

Andrew pointed to an area of activation on the side of the brain. This region was about a centimeter higher than the reward system, and it was located in the middle of the cortex. Since the usual landmarks of the human brain didn’t apply, we were left guessing what part of the dog brain we were looking at.

Cross-referencing an atlas of dog brain anatomy, I asked, “Is that the motor cortex?”

Andrew shrugged and said, “It’s in the middle of the cortex, about where the human central sulcus would be.”

But the dogs weren’t moving in our experiment. Why would we see activity in the motor area?

“Mirror neurons,” I said.

Mirror neurons are a specific type of neuron in the brain that fires both when an animal initiates a movement and when it observes the same type of movement in another animal. They were originally discovered in the early 1990s by researchers recording the brains of monkeys. The scientists were primarily interested in how the motor system functioned, especially when the monkey decided to reach for an object. They implanted electrodes to record from the area of the brain just in front of the central sulcus, called the
premotor area
. These neurons did, in fact, begin firing just before the monkey moved its hand. Somewhat accidentally, though, the scientists also noticed that these neurons fired when the researchers reached into the cage to replace the object that the monkey was trying to get, even though the monkey wasn’t moving at that moment. They were dubbed mirror neurons because they seemed to mirror both observation and action. They fired when the animal initiated a motor act as well as when somebody else performed a similar action, and it didn’t seem to matter whether it was a monkey or human hand that was doing the reaching.

It wasn’t long before researchers began searching for mirror neurons in humans. Using fMRI, several experiments found evidence for the same mechanism operating in the premotor area of the human brain, as well as a number of other areas. Rather than controlling the movement of a particular part of the body, these mirror neurons seemed to control action
goals.
For example, a baseball pitcher tries to throw the ball in the strike zone. The mirror neurons in a pitcher’s brain don’t control the muscles of the arm directly. Instead, they act like a guidance system so that all the muscles of the body act together to reach the ultimate goal of depositing the baseball in the catcher’s mitt at the desired location. And if a pitcher watched someone else doing the same thing, the pitcher’s mirror neurons would fire while he observed—as if his brain were simulating the act of pitching.

The interest in mirror neurons continues to intensify. At a basic scientific level, these neurons seem to play a key role in linking action production with action observation and to allow animals to understand the actions of other members of their species from their own perspective. Many researchers have suggested that mirror neurons are the basis of empathy. If this turns out to be true, then mirror neurons not only allow us to simulate the actions of each other from the inside, but they may allow us to feel what someone else feels too.

The role that mirror neurons play in feeling empathy continues to be debated, but the evidence suggests a route to empathy through imitation. Humans, in particular, have strong innate tendencies to imitate each other. When someone smiles at us, we can’t help but smile too. This type of imitation seems to be wired from birth. Infants smile in response to adults smiling at them and also initiate smiles to receive the same response from their parents. The mirror neuron system, by serving as the link between observation and action, may control this type of imitative behavior.

It is through imitation that we begin to feel what someone else feels. Several experiments have shown that the more people imitate each other, the more empathic they become. Although it remains to be proven that mirror neurons are the basis for empathy, it does seem clear that they play an important role in the precursors to empathy. Without the mirror neuron system, it would be unlikely that people would have any empathy at all.

Apart from monkeys watching humans reach for stuff, nobody had demonstrated cross-species mirror neuron activity. Even with the monkeys, a human hand looks an awful lot like a monkey hand. They both have four fingers and an opposable thumb.

But dogs don’t have thumbs. They don’t even have hands.

And yet Callie’s and McKenzie’s motor cortices were activating in response to our hand signals. They weren’t moving, so maybe this represented mirror neuron activity. But this would be considerably more complex than monkeys observing human hands. If the activity we found came from mirror neurons, this would mean that the dogs were performing some kind of action mapping between a human hand and their forepaws. My mind began to spin with the implications.

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.