A recent study using brain-imaging technology has been able to detect a similarity between our brain and our best friends'. In Hungary, the Comparative Ethology Research Group was able to identify that dog's brains respond to vocal sounds the same way human's brains do. Basically, when you talk to your dog, he is listening to you and eventually understands what you tell him.
The dogs pictured above were trained to lie motionless in the MRI scanner while scientists imaged their brains. The patterns recorded from their brains were those while sounds of laughter, whining, crying and barking were taking place. This same study was then done on 22 humans to make a valid comparison of the results. What the scientists found was that the same parts of the brain lit up for both human and dogs while they listened to the specified sounds. There was a stronger relationship with dogs responding to the sounds of dogs and humans to those of humans, but that was to be expected. The overall results proved to show that dog's brains are very similar to those of humans in response to their listening and interacting with each other.
Andics, the head of the study, says that "dogs and humans share a similar social environment". This makes sense as to why humans and dogs can communicate and get a long so well. However, Monique Udell from Oregon State University says that "similar brain activity does not necessarily mean that dogs and humans experience sounds and vocalisations the exact same way". So either dogs really do understand and listen to us, or they've just evolved to respond to human's voices from having so much exposure to them throughout the ages. Whatever the reality of it may be, the study proves that dogs can tell when you're happy or sad.
If you're still not convinced, you can check out the video below, it's of how they actually went about doing the study with the dogs. Remember that regardless of this study, you should always love your puppy because they love you back.