Whilst we wait for a miracle in medical research there have been press reports in recent times on the good effect of high level brain activity and staving off the onset of Alzheimer's. Just Google Alzheimers and crosswords.
I'm not sure what the effect of three-dimensional crosswords is, but they certainly exercise the mind and just as importantly are great fun, particularly as a group activity.
www.calendarpuzzles.co.uk offers such ground-breaking puzzles for free. Sovers who enjoy a puzzle, or even just a wacky clue are asked to consider doing something for a person or group in need. This could be an action or a donation to a charity of their choice.
I do not have very much money, but whilst my brain is still working (albeit 50%) I would be very happy to design a puzzle for your charity. No charge of course - that would be my donation!
Just contact me here or at firstname.lastname@example.org.