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.