Emma Thompson's mother is called Phyllida Law -- they did a movie together called "The Winter Guest", in which they play mother and daughter. Anyway, Phyllida Law's mother had dementia, and there's a little clip on Youtube that you might be interested in. Just google "phyllida law's mother's dementia" and it should take you there.
In the meantime, I'm binge-watching Poirot as I sprained my back abt a month ago and am still not better.