Your brain needs to be sharpened. Is this just the medicine for you?
First, the game tests your brain to see how heavy it weighs: the heavier, the better. I don't think that it's pretty much an accurate representation of your brain's actual weight, but I guess you've figured that out if you had any common sense.
Anyway, after that part, you can "train" yourself to get a heavier brain by playing the minigames included in the package. And if the game thinks that your brain can handle it, it increases the speed and difficulty that the mini-game normally has. For example, the game wants you to guess what the face of a person who just passed has. In Easy, the differences in your choices are obviously, while in a higher difficulty setting, the differences are almost minute. The game determines that only in the speed of which you process the solution to these mini-games, which probably gives it the feeling that it's training your brain unofficially.
Still, if you're the type who likes family fun, you will get a kick out of this. Otherwise, it's pretty advisable for you to skip this minigame collection. If you want a serious mini-game collection that doesn't screw with your brain with hypothetical crap, try WarioWare.