It’s well known that an idle mind is the devil’s playground. Which makes me wonder if an idling engine is the devil’s mode of transportation. Which I’d realize is nonsensical, except that now I’m thinking of this beautiful California mountain town called Idyllwild, reminding me how Kennedy Airport used to be Idlewild Airport, which is mentioned in the theme song of the 1960s TV show “Car 54, Where Are You?” Which makes me wonder if 54 is a prime number. But then I feel embarrassed—it’s an even number, ninny!—reminding me of that really embarrassing thing I once did.

A wandering mind can bollox up all sorts of useful activities—like trying to finish the first paragraph of a newspaper column with a clearly stated thesis. In studies asking subjects at random what they’re thinking, researchers have found that during some tasks, we spend about half our time “mind-wandering,” that is, having thoughts unrelated to the work at hand.

How is mind-wandering generated in the brain? One finding is provocative. Stick people in a brain scanner, and when their minds are wandering, one region that activates is the dorsolateral prefrontal cortex (dlPFC). This is surprising, because it’s a relatively recently evolved brain region, central to executive functions like long-term planning, working memory and decision-making. It’s the last brain region that you would expect to get involved with something as frivolous as mind-wandering.

Perhaps the activation of this brain region is actually a response to mind-wandering rather than a mediator of it. Suppose the mind-wandering brain circuit, wherever that is, activates and the dlPFC tries to put a brake on it, essentially saying: “Hey, we’re trying to get something done—enough daydreaming!”

A recent study examined these issues and produced what was, to me, an unexpected finding. Writing in the Proceedings of the National Academy of Sciences, Vadim Axelrod of Bar-Ilan University in Israel and colleagues stimulated the dlPFC in subjects by giving them a repetitive task (monitoring number sequences on a screen and pressing the space bar whenever a certain digit appeared). Researchers asked the subjects intermittently what they were thinking about and, predictably, rates were high for “task-unrelated thoughts.” Their minds were wandering.

Click for more from The Wall Street Journal.