Anything that promotes health or provides active or interactive stimulus to the mind fits. Sci Am just picked out six from a giant bucket. Crosswords, reading Hacker News, and (trying to) solve P = NP all have similar effect.
But that big bucket is sort of like the old axiom about filling a jar with stones. First you have to put in the biggest ones. And here I think they've ranked them pretty well in the list. Exercise and nutrition come first and are easy to forget especially with classical notions of Reason and what our daily demands are.
