Your parent has dementia, so you would naturally expect her to be forgetful. Yet there are certain things that she seems never to forget. Is she really forgetting as much as she seems to be, or is she choosing to use "selective memory" for her own incomprehensible and crazy-making reasons?

Every night for 60 years your father has wound the big old alarm clock on his nightstand before going to bed. He never, ever forgets. Yet, he can't seem to remember to take the pills you placed RIGHT NEXT TO THE CLOCK so he can't possibly miss them.

The fascinating thing about all of the dementias is that no two people experience it in exactly the same way. However, it's generally true that older memories seem stick around longest (to put it very, very simplistically). So, I might remember that every night I wind the clock, because I have been doing it every night for a long time. I have repeated this task over and over again, always in exactly the same way, so it's rooted pretty strongly in my long-term memory.

On the other hand, when you tell me to remember to take the pills beside the clock, this is brand new information. It doesn't belong to any particular unchanging pattern or routine. If I have dementia I am likely to lose this information immediately.

The same holds for who might have visited this week, or that I had my hair cut today, and that I have an appointment tomorrow. These are random events and new information. They are difficult or impossible information for me to hold on to. It does no good to try to "remind" me, because there may be no memory stored in my brain for me to retrieve.

This kind of "selective" memory is not by choice. Just about 100 years' of observing people with Alzheimer's and the other related dementias has demonstrated that this is the way the "demented" brain seems to work. "Last in, first out" is a cliché, but it is so true for the memories of most people with dementia classed as "moderate" or worse.

This is why it seems to be so important to establish a regular routine for those with dementia. It is difficult to do at home, where every day has it's own interruptions and small crises, but it really pays to try. In the best dementia specialized facilities, the routine is prescribed down to 15 or 20 minute intervals, and rarely varies. Residents become accustomed to the routine. Even if they can't describe it, they seem to be happier and function better when there are no surprises and nothing new to cope with.