You are correct. Alzheimer can not be prevented by reading maps or solving word puzzles. In my opinion it is plaque buildup just like plaque in heart arteries.
Best defense is exercise! Regular Exercise is keeping me away from heart attacks, strokes, Alzheimer’s etc nearing age 83.
Ah, but what is the plaque?
One of the latest ideas is this: Groundbreaking New Revelations on Alzheimer's Disease