The puzzles look easy, and mostly they are. Given three words  “trip,” “house” and “goal,” for example  find a fourth that will complete a compound word with each. A minute or so of mental trolling (housekeeper, goalkeeper, trip?) is all it usually takes.

But who wants to troll?

Let lightning strike. Let the clues suddenly coalesce in the brain  “field!”  as they do so often for young children solving a riddle. As they must have done, for that matter, in the minds of those early humans who outfoxed nature well before the advent of deduction, abstraction or SAT prep courses. Puzzle-solving is such an ancient, universal practice, scholars say, precisely because it depends on creative insight, on the primitive spark that ignited the first campfires.

And now, modern neuroscientists are beginning to tap its source.

In a just completed study, researchers at Northwestern University found that people were more likely to solve word puzzles with sudden insight when they were amused, having just seen a short comedy routine.

“What we think is happening,” said Mark Beeman, a neuroscientist who conducted the study with Karuna Subramaniam, a graduate student, “is that the humor, this positive mood, is lowering the brain’s threshold for detecting weaker or more remote connections” to solve puzzles.