In dogs, we found that activity in the caudate increased in response to hand signals indicating food. The caudate also activated to the smells of familiar humans. And in preliminary tests, it activated to the return of an owner who had momentarily stepped out of view. Do these findings prove that dogs love us? Not quite. But many of the same things that activate the human caudate, which are associated with positive emotions, also activate the dog caudate. Neuroscientists call this a functional homology, and it may be an indication of canine emotions.

The ability to experience positive emotions, like love and attachment, would mean that dogs have a level of sentience comparable to that of a human child. And this ability suggests a rethinking of how we treat dogs.

DOGS have long been considered property. Though the Animal Welfare Act of 1966 and state laws raised the bar for the treatment of animals, they solidified the view that animals are things — objects that can be disposed of as long as reasonable care is taken to minimize their suffering.

But now, by using the M.R.I. to push away the limitations of behaviorism, we can no longer hide from the evidence. Dogs, and probably many other animals (especially our closest primate relatives), seem to have emotions just like us. And this means we must reconsider their treatment as property.