Among his findings is that the part of dogs’ brains that light up when they hear their owners’ voices is the same part of the human brain that lights up when we are fond of someone or something. His first book was “How Dogs Love Us.”

By looking at the lemon-sized dog brain, he has shown, for instance, that, based on how the reward center lights up, a dog likes praise as much as it likes hot dogs. In testing outside of the M.R.I., Dr. Berns has also found that, given a choice, some dogs prefer their owners to food.

He agreed that the hypersociality of dogs is what makes them special rather than particular cognitive abilities. “It’s hard to demonstrate any cognitive task that dogs are superior in,” he said. But he pointed out that “ultimately the difficulty is in saying what is a cognitive function and an emotional function.”

Alexandra Horowitz, head of the Dog Cognition Lab at Barnard College, and a prolific writer on dogs, also addressed the question of love briefly in her new book, “Our Dogs, Ourselves.”

Without doubt, dogs have feelings, she wrote, but she cautioned that just as certainly, those feelings were not the same as human feelings. Nor, she argued, should we assume that dogs are in between robot and homo sapiens on an emotional spectrum. She wrote in her book , “For all we know, dogs’ emotional experience is far more elaborate than ours.”

Central to that experience, although unknown in its complexity, is the pleasure a dog experiences in the presence of humans. The intensity of that pleasure and the ease of triggering it, Dr. Wynne said, is built into the dog genome.