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“We could train the dogs with a hand signal that indicated they would receive a hot dog,” I said.
“If the dogs learned the association between the hand signal and the treat,” Andrew agreed, “we should see caudate activity to the hand signal.”
“Just like Schultz’s monkeys,” I concluded.
Lisa spoke up and pointed out a flaw in this reasoning.
“How would you know that the dogs had learned the hand signal?” she asked. “After all, they’re not doing anything.”
She had a point. All of behaviorist learning theory depended on the manifestation of either a response, like drooling, or a behavior to indicate that the animal has actually learned something. We would have only the brain.
“We’ll have to rely on the dogs’ caudate,” I said. “A response there would be proof that they learned the signal. We could also look for other signs, like the pupils dilating in anticipation.”
There was another problem. An fMRI scan measures brain activity indirectly. What it actually measures are changes in the oxygen content of tiny blood vessels in the brain. When neurons fire, the surrounding blood vessels expand a little and let in more fresh blood for the neurons to replenish their energy storage. The scan picks up these changes in blood flow, and from that we deduce which neurons were active. But there is a catch. The brain is always on. It is a myth that we use only some small percentage of our brains. The truth is that we use all of it—just not all at once. Because the brain is always on, and blood is always flowing, fMRI can measure only changes in activity. When designing fMRI experiments, you always need a comparison, or baseline, condition.
Callie would be in the sca
To measure the response to a hand signal, we needed another hand signal as a comparison condition. This way, everything would be the same—holding still, watching the handler and even the handler’s movements. We would vary the meaning of the signals.
“How about another hand signal,” I suggested, “which means something else?”
“Like what?” Andrew asked.
“A different type of food,” I said. “Something the dogs don’t like as much as hot dogs.”
“Like what?” Lisa asked. “Sheriff likes everything.”
It was a fine line. We wouldn’t want the dogs to eat something nasty. We needed something that they would eat but not like as much as hot dogs. Dogs are mostly carnivores. It seemed logical that they wouldn’t value a vegetable as much as a piece of meat.
“How about peas?”
Everyone nodded as they envisioned how this would work. I held up my left hand in a “stop” gesture.
“Suppose this means ‘hot dog.’ ” I thought briefly about holding up my right hand for “pea,” but as we didn’t know the extent to which dogs distinguished left and right, this seemed like a bad idea. Instead, I held both hands flat in front of my chest, pointing toward each other. “And suppose this means ‘pea’?”
Mark nodded.
“Those signals should be easily distinguishable to a dog.”
The rest of the team agreed.
It was decided. The first canine fMRI experiment would be “Peas versus Hot Dogs.”
Over the next week, Andrew and I formalized the design of the experiment, which is in some ways like writing a screenplay. Every detail has to be pla
The most important detail, though, would be the timing of the experiment. Each repetition would have four elements. First, the dog would place her head in the chin rest. Because of the associated movement, this would cause artifacts on the scan being acquired at that moment. We would need to wait at least two seconds for the next scan to begin. Once the dog was settled in the chin rest and enough time had passed for the artifacts to decay, we would proceed to the second element, the hand signal.
Melissa and I would be giving the signals to our dogs, and all of our attention would be focused on Callie and McKenzie. It would be too much for us to randomly decide on the fly which hand signal to give, so Andrew would be standing next to us with a pregenerated list of the order of signals. He would hold up one finger for hot dogs and two for peas. The handler, facing the dog in the sca
We knew that the fMRI response would not be instantaneous. The blood vessels surrounding the neurons take a few seconds to dilate, peaking after six seconds and returning to baseline twenty seconds after that. This profile is called the hemodynamic response function, or HRF, and it is a bugaboo of fMRI experiments. The lag in response meant that the dogs would have to hold perfectly still for the time it took the HRF to peak and decay. This delay period was the third element. Ideally, the dog would hold still for twenty seconds. But I would settle for ten, which would be enough time to capture at least the peak of the HRF.
Mark and Andrew and I debated whether we should just flash the hand signal for a second and then wait ten seconds before giving the reward. The alternative would be to hold up the hand signal for the entire waiting period. In the end, we opted for the latter. If we flashed the signal briefly, we wouldn’t know whether the dogs were paying attention to the appearance of the hand signal or its removal. Both could be salient. To make sure that they paid attention to the signal’s appearance, it seemed prudent to keep our hands up until we gave them the treat, which was the fourth element and the end of each sequence.
This would be easy for the hot dog repetitions. Left hand up for the signal, and then deliver the hot dog with the right hand. The pea repetitions, though, required both hands as part of the signal. This meant that the pea would have to be palmed in the right hand.
To make sure we were smooth on scan day, Melissa and I practiced all the elements over and over again. The dogs might pick up subtle changes in our body language, but there wasn’t much we could do about it other than practice.
At home, Callie and I continued working with the mockup. She was so used to it, even with the sca
Callie was ready. If she knew what was about to happen, she gave no sign.
I, on the other hand, could barely contain myself. We had made a lot of progress since the dress rehearsal. The redesign of the chin rest, the modification of the scan parameters, and the choreography of the experiment were all positive developments. But still, there was a lot riding on this. Tomorrow, we would know for sure whether the Dog Project would work.