Where does the smile come from?

She rocks gently as she holds the doll. She smiles and strokes the hair. Then she tucks up the doll in the blanket. The doll is placed on the walker and she rocks it back and forth. Other people pass by and she takes no notice. It is just her and her “baby”. Someone passes and comments on how well she is doing. Hours can pass and she seems happy. Next to her is a man who sits and stares into space. He doesn’t want to join in any of the activities. Someone said that people with Alzheimer’s do not remember the emotion attached to an old memory. So why does she play with the doll? Why does she seem to be happy?