Dogs' brains can tell the difference between distinct negative facial expressions, such as anger, fear and sadness, according to researchers who used functional magnetic resonance imaging (fMRI) scans on pet dogs.
Dog owners have long noticed that their pets are remarkably skilled at interacting with people and reading facial expressions, but until now science had not established exactly how a dog's brain processes that information.
How the study worked
Functional MRI is a scanning technique that measures brain activity by tracking changes in blood flow, and it is widely used in human neuroscience to study how the brain reacts to different stimuli. To find out whether dogs simply register facial expressions in a general way or whether their brains can tell apart specific emotions of the same type, researchers used the technique on the animals.
The dogs were awake and unrestrained during the scans, and had been trained to lie still inside the scanner while looking at photographs of human faces they had never seen before. The research was split into two main experiments.
The first involved eight dogs and compared their brain responses to happy faces against neutral ones. The second involved 12 dogs and showed them photographs of human faces expressing four basic emotions: happiness, anger, fear and sadness.
What the brain scans showed
In the first experiment, looking at happy faces strongly activated a network of areas on the right side of the dogs' brains. That network included the temporal cortex and the caudate nucleus, a region that in dogs is closely linked to processing rewards such as food or familiar smells. The researchers said this suggests human smiles carry a positive, rewarding emotional meaning for dogs.
In the second experiment, scientists used artificial intelligence to analyze signals from that same brain region. The system could accurately tell when a dog was looking at a happy face compared with any of the negative emotions of sadness, anger or fear. However, that specific happiness-linked area of the brain could not distinguish the negative emotions from one another.
It was only when the researchers analyzed the dogs' brains as a whole that a distinction between the negative emotions emerged.
Fear stood out in particular. The researchers said it was easily distinguishable in the dogs' brains and that this made evolutionary sense, since reacting to another animal's fear is crucial to safety and survival.
Limitations of the study
The research relied heavily on Border Collies, a breed traditionally used for herding sheep and known for being highly attentive to human cues and easy to train. The researchers cautioned that because of these traits, the results should not be generalized to other types of dogs without caution.
The study also had the dogs look at static, two-dimensional photographs in a laboratory setting. In real life, dogs interact with dynamic facial expressions and the whole body of the people around them, which provides much richer cues for everyday communication, the researchers noted.
