Using brain-game apps to improve mental acuity are good as far as they go. You get better at playing games but not necessarily smarter or fitter.
Total brain fitness requires constant stimulation from the world around you. As one expert puts it: “Your brain doesn’t know how old it is, and what it wants to do is learn.”
Constance Gustke, writing in The New York Times, gives a comprehensive overview of the current thinking on the best ways to improve brain fitness.