Mirror Neurons are a part of the brain that activate when we perform an action as well as when we see that action performed by others. For example, when we see someone pick up a cup a part of our brain will activate as if we had been the one to do that action.
It becomes much more important for when we interact with other people. If we see someone smile, the mirror neurons will fire up as if we had been the ones to smile.
However, there are multiple circumstances in which a person’s brain may not be able to act like that. With Asperger’s, it’s theorized that the mirror neurons don’t fire when the individual detects subtle facial gestures. This causes social issues, because they don’t pick up on cues as easily as others. They still have emotions like others, but it is difficult to see what other people are thinking or feeling.
It’s also important to note that strokes can damage a part of the brain and cause similar symptoms, and depression has also been observed to do this as well.