At SharpBrains, Alvaro Fernandez has an interview with Yaakov Stern, a leading proponent of the “cognitive reserve” theory of Alzheimer’s disease:

which aims to explain why some individuals with full Alzheimer’s pathology (accumulation of plaques and tangles in their brains) can keep normal lives until they die, while others -with the same amount of plaques and tangles- display the severe symptoms we associate with Alzheimer’s Disease.

Dr. Stern studies the effect of behavioral differences (specifically related to cognition, including intellectual as well as social life) on Alzheimer’s progression and disease severity, and has come to believe that individuals who make certain lifestyle decisions can accumulate cognitive capacity (physically manifest as increased connections between neurons, rather than an increase in the number of neurons per se — that would be a “brain reserve,” and apparently that’s a whole other theory).

The take-home message from his findings is that more mental activity (and more varied types of activities) is better. Quite simply: Use it or lose it.