I once worked at a propane distributorship where I learned two things that stuck—how to back up a trailer holding a 1,000-gallon tank so that its four steel feet would settle squarely on small blocks.

Technically, the brain isn’t a muscle, but if you don’t use it, your brain gradually turns to mush. It starts with your swearing that you know a word or a name and that it’s at the tip of your tongue.

How good is your working memory? Whether it involves holding a telephone number in your head long enough to write it down or trying to keep track of all the items on a grocery list, having a good ...