My sister, my mother and I watched as our Dad's horizons shrank (he died in 2008). It may well have also been due to his sight and hearing going and not being able to follow conversations, feeling more and more cut off, but being a man, refusing to recognise or admit this. His world consisted entirely of himself and his demands on our mother, who was nearly 90 herself and had given up ten years of her life coping with him.
We are so lucky that our mother is still aware of the needs and lives of others, and showing no sign of self-centredness.
She still always asks her cleaning lady about her daughters, even chatted to the plumber about how he ran his business, and always asks me about my DC and DGC, and is so grateful to my sister who leads a busy life, but does all Mum's washing, house maintenance and finances, organises care and doctor's appointments etc.
Even though she can't see or hear as well as she admits, her mind is still open to things around her. She can't follow the news, but her horizons are still far wider than 6" from her armchair.
With our dad, I also suspect that he was in pain, which does make you more self-centred.
I will also risk a speculation that it is more a Man Thing.
Once you have done all you can to relieve pain, and seen to it that sight and hearing are as good as they can be, there is not much you can do once those horizons have closed in, and they will no longer react to any conversation about other people's problems or happy events.
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