This is my personal opinion.
I believe the brain is akin to a hard drive. It has to be formatted to be used. Formatting comes when new things are learned. The more we learn the bigger the area of our brain that becomes formatted. When Alzheimer’s disease strikes, if a large area of the brain has been formatted, the brain can reroute signals and continue on. If a large area of the brain has not been formatted, disease such as Alzheimer’s can stop a person in their tracks.
A person that is very emotional for long periods of time does not format much of their brain because emotions originate in a different part of the brain. I think this is why the Nun Study turned out like it did.
Many of the nuns had the pathology of Alzheimer’s disease but showed no symptoms. Nuns are known to not have much depression and learn new things on a continual basis.
This is just my opinion and I have not even been to college, so keep that in mind. Also though, help for finding a cure or prevention ideas may come from anyone.