Callie testing the fit of the boogie board chin rest.

(Gregory Berns)

The next day, I trimmed up the foam block and glued it to a piece of plywood that would span the diameter of the head coil. The plywood was cut to just the right length so that the whole chin rest placed Callie’s head in the center of the coil while allowing space beneath it for her paws to stick forward.

With the contraption on the floor, I called to Callie, “Coil!”

She scooted in and immediately plopped her head in the rest.

“Excellent!” I exclaimed, and gave her a piece of hot dog. She happily swallowed it and placed her head back down. She waited for more.

Next, we tried it with the earmuffs. Callie still didn’t like them, but with enough hot dogs, I coaxed her into the coil while wearing the muffs. I tapped the new chin rest, and she dutifully placed her head in the cradle. The muffs slipped back a little, but I was able to slide them forward again over her head. Callie’s eyes dilated as she anticipated treats.

“You are such a good dog!”

Callie appeared so comfortable in the new chin rest that I began lengthening the time she had to stay motionless before giving her a treat. In a dozen repetitions, she was holding absolutely still for up to ten seconds at a time. That was more than enough. We would be able to get at least five full scans of her brain in that period.

The new chin rest design looked very promising. I had already booked the MRI for Dog Day, which was now less than two weeks away. The scanner was reserved for four hours to allow us plenty of time to let the dogs get comfortable in the scanner, but at $500 an hour, this was going to be an expensive experiment. Of course, we wouldn’t know if it was successful until we actually tried it at the scanner. The new chin rest was the best shot we had, so I made one for McKenzie too.

The full monty: Callie in the final version of the chin rest.

(Gregory Berns)

Both dogs made rapid progress with the new chin rest. McKenzie, of course, was already a champ at holding still. The new rest also made it easy for the dogs to consistently place their heads in the same location. There was only one last detail to work out before scan day.

What, exactly, was the scientific question we hoped to answer by scanning dog brains?

14

Big Questions

WITH THE NEW CHIN RESTS, Callie and McKenzie were cruising along in their training. I was routinely blasting the scanner noise at 90 decibels, and as long as Callie had the earmuffs on, she didn’t seem to mind. Scan day was two weeks away. Andrew had circled the date on the lab calendar and written “Dog Day” in bold red letters.

None of us expected to pull off a complete scientific experiment on the first try, so we held on to modest expectations. The first and most important goal of the scan session would be the acquisition of a sequence of fMRI images that weren’t contaminated by motion artifacts. I would consider the session a success if we obtained ten images in a row without the dog moving. That would mean holding still for a twenty-second interval in the scanner. Considering how well the dogs were doing in their training, that seemed entirely possible.

On the off chance that the dogs surpassed our expectations and miraculously held still for several minutes, we would then have the opportunity to collect enough data to go beyond simply proving the viability of the Dog Project. We might actually get to answer a scientific question about canine brain function, which, of course, was the whole point. I didn’t expect to be able to do this on the first go, but it’s always best to be prepared.

I called a meeting of the core Dog Project team—Andrew, Mark, and me—but since everyone in the lab was rooting for this, it turned into an impromptu lab meeting.

“We’ve got two weeks until Dog Day,” I began, “and we have to nail down the experimental task that the dogs will do.”

Because the scanner noise was so loud, the dogs would not be able to hear vocal commands. That left hand signals as the primary means of communication while in the scanner. Up until now, we had purposely avoided using hand signals because we didn’t know what kinds of signals we would use and what the dogs should do with them. It was time to figure that out.

“Not much is known about the functional organization of the dog brain,” Andrew said. “We don’t even know what parts of the dog brain are responsible for basic functions like vision and hearing.” What we did know came from some unsavory experiments over a century old. In 1870, a pair of German scientists used the then new technology of electrical energy to directly stimulate the brains of animals. By sticking their electrodes in different parts of the brain, they discovered that the electricity could cause an animal to move its limbs. Sadly, they used dogs for this experiment, even puppies—a trend that continued into the 1970s. The end result of this research was the knowledge of which parts of the dog brain controlled movement. But for the Dog Project, we couldn’t study the parts of the brain that controlled movement because the dogs weren’t supposed to move!

“Let’s go with our strength,” I said. “Our lab has spent the last decade studying the human reward system. We know a lot about how it works. There isn’t any reason to expect the dog’s reward system to be any different from the human one.”

“Reward-prediction error experiment?” Andrew asked.

The brains of all animals appear to act as prediction engines. Prediction, after all, is key to survival. If your brain weren’t predicting what would happen next, you wouldn’t be able to walk across the street without being hit by a car. Most of the brain’s predictions have to do with things in our environment, like cars, and things that other people are doing. The caudate nucleus (located within the basal ganglia) and the parts of the brain that feed into it are concerned with predicting rewards.

In the early 1990s, Wolfram Schultz, a Swiss neuroscientist, measured the activity of neurons in monkeys’ brains while they were trained on a simple classical conditioning task. When a light turned on in a monkey’s cage, it received a squirt of fruit juice in its mouth. Just like Pavlov’s dogs, the monkeys quickly began to anticipate the juice when the light came on. Schultz discovered that the neurons in specific parts of the brain followed the same pattern. Initially the neurons fired in response to the juice, but once the monkeys had learned the association with the light, the neurons fired to the light, not the juice. The neurons that showed this pattern were located in the heart of the reward system, the caudate.

Since Schultz’s discovery, neuroscientists have learned that these neurons don’t signal things that are pleasurable. Instead, they fire when something unexpected occurs that indicates something good is about to happen. If something is unexpected, then that means the brain made an “error” in predicting it. For this reason, scientists call these events reward-prediction errors.

We know where reward-prediction errors occur in the brains of monkeys and humans. Dogs, we figured, should be no different. And because the caudate is a well-defined structure, it made sense that we would be able to identify it in the dogs’ brains—assuming, of course, they held still for the MRI.