The neurologists and neurotherapists for a family member who is a stroke survivor have been pretty consistent in saying that cardiovascular exercise and regular social engagement seem to be the most promising activities to stem cognitive decline.

Yes, I think both things can be true. And also, we haven't had decades of mental activity being mostly optional, so we're not yet seeing the consequences nor science of long-term impact.

In the 1950s, many doctors were convinced that exercise was actively harmful and running was dangerous.