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Dogs may understand more than just the words we say. A new scientific study suggests that they can also notice human facial expressions and may recognize different emotions such as happiness, anger fear and sadness. Researchers from the  University of Vienna in Austria studied dogs’ brains to understand how they react to human faces.  Their findings were published in the scientific journal iScience. How the study was done In the first part of the study researchers used MRI scans to study the brains of eight dogs. The group included six Border Collies, one Labrador and one Golden Retriever. The dogs were shown pictures of unfamiliar people with happy or neutral facial expressions. When the dogs saw happy faces certain areas of their brains became more active. These areas are linked to thinking rewards and positive experiences. Researchers found strong activity in areas such as the temporal cortex and caudate nucleus.  The caudate nucleus is connected with the brain’s reward system and may also respond to social rewards. According to senior researcher Laura Cuaya, this suggests that a happy human face may have a positive emotional meaning for dogs even when the person is a stranger. Dogs may tell different emotions apart The researchers then wanted to know whether dogs could also recognize negative emotions. Twelve dogs were shown human faces expressing happiness anger, fear and sadness. Their brain activity was recorded and studied using machine learning methods. The results showed that dogs’ brains reacted differently to angry fearful and sad faces compared with happy faces. The researchers also found different brain activity patterns for each negative emotion. This suggests that dogs may be able to tell these emotions apart rather than seeing all negative expressions as the same. Dogs notice small changes First author Raul Hernandez Perez explained that humans can often understand emotions from very small changes in a person’s face.  Dogs may also pay close attention to these small changes. This ability may help explain why dogs are so good at understanding people. Unlike humans and monkeys dogs did not develop these social skills through the same evolutionary path. Instead thousands of years of living closely with humans may have helped dogs become highly sensitive to our behavior and signals. Interestingly both researchers are not only professional colleagues but also life partners. Their own two dogs, Odin and Kunkun were also part of the study. It is not only about the face The researchers say dogs do not depend on facial expressions alone. They can also notice changes in our voice body movements, behavior and even smell. So when a dog seems to know that its owner is happy worried or upset it may be combining many different signals at the same time. Training dogs for MRI scans The dogs had to receive special training before taking part in the research.  They learned to stay still inside an MRI scanner for short periods. At first they were trained to remain still for only one or two seconds.  The time was slowly increased as they became more comfortable. They were also introduced to the scanner the equipment and the sounds it made.  One of the hardest parts was teaching the dogs that doing nothing was actually their job. The dogs took part voluntarily and could leave whenever they wanted. The study has some limits The study was small and most of the dogs were Border Collies. This breed is known for being intelligent and good at understanding human social signals. Because of this the results may not be the same for every dog breed. More research is needed to find out whether different breeds understand human emotions in different ways. Scientists also want to learn how dogs use these emotional signals in everyday life. The study does not prove that dogs experience happiness sadness or fear in exactly the same way humans do. Scientists cannot directly know what a dog is thinking or feeling. However the brain activity does suggest that human facial expressions carry emotional information for dogs. The bond between humans and dogs goes far beyond simple commands. Dogs can pick up signals from our faces voices movements and behavior. This ability may be one of the reasons why the relationship between people and dogs is so strong.