Can and Can't

My mother, who can recite vast chunks of the Bible, having been a Christian since University.
My mother, who can reel off medicines and their ingredients, or the names of the small bones of the hand and foot, having been a GP for 40 years.
My mother, who can't remember whether she has been out today, and can't remember which grandchildren belong to which family although she can recognise faces.
And my mother, who can't remember the answer to the question she has just asked.
Dementia.