[JacobIrwin]

Enjoyed the read, but not so sure that "caffeine is a zero-sum game." - http://www.futurity.org/caffeine-stimulates-long-term-memory...

[ta43434]

From your link:

    The subjects—*none of whom regularly ate or drank caffeinated products*—

Tolerance is the main reason why caffeine is a (mostly) zero sum game.