Does anyone know what dementia patients think about?

Mom lives in the moment. She has good moments and bad moments. We just go with the flow and redirect her if it is a bad moment, change the subject, turn to a happy memory deep in her past.

My Dad has moderate dementia and I know he feels fear and anger. When he asks for my Mother and I tell him she is gone, he has that terrible hang dog look and it is excruciating for me, so I don't say that anymore. He calls out for my stepmother when he is in bed alone, begging her to come to bed so he won't be alone. He is fearful and I am sure lonely, when she is busy or gone to the Dr. I believe my Dad feels all the normal emotions, he just doesn't have continuity of thought, so he feels a lot of anxiety.