Why do songs get stuck in your head? asks a reader.

It could be the pop song they played on the radio from morning until evening ("I’m gonna soak up the sun…"). It could be the jingle from a commercial you saw last night ("Break me off a piece of that Kit-Kat bar…"). Or it could be the boat ride you went on at Disney World ("It’s a small world after all…."). Whatever the trigger, you’ve got a snippet of music playing over and over in your mind. And it’s driving you a little crazy.

Like yawning, catchy tunes-- especially those with words-- seem to be contagious. Just mention a song like "Dancing Queen" (or nearly any Abba tune, for that matter), and someone within hearing distance will get it stuck in their head. Others can’t hear the words "My Sharona" without enduring hours of relentless repetition, thanks to The Knack.

So why does the brain act like a broken jukebox, the same piece of music clicking on again and again, a la "Groundhog Day"? The last several years have seen a small flurry of research into the viral brain tunes known as "earworms." Like the earworms wielded by a diabolical Ricardo Montalban in "Star Trek: The Wrath of Khan," musical worms enter our ears and burrow straight into our brains. The reason seems to involve the human brain’s love of patterns, and its dogged compulsion to fill in musical blanks.

A survey of college students by marketing professor James Kellaris of the University of Cincinnati found that nearly everyone experiences stuck songs. While certain songs, like bad pennies, turn up again and again on earworm lists, Kellaris says that each of us tends to be bedeviled by our own do-over ditties.

Researchers say that the music most likely to get lodged in the brain has a simple, catchy, repeating tune and/or lyrics (or even an unexpected musical twist), and has been heard frequently on radio or TV. The brain seems to dip into its repeating repertoire most often when we’re tired or anxious.

Dartmouth University researchers used MRIs to image the brains of volunteers as they listened to music, including the earworm-worthy theme from "The Pink Panther." The catch: Bits and pieces of the tunes were missing. Researchers found that the auditory cortex in the listeners’ brains remained active during the gaps in familiar tunes, automatically filling in the musical blanks. In effect, people couldn’t stop their brains from continuing a well-known tune. It’s in the auditory cortex, researchers think, where songs become musical memories.

In our music-heavy environment, with tunes playing in stores, restaurants, elevators, and in every I-Podded ear, stuck songs are a fact of life. How to switch off the inner music? If it’s July but your brain is playing endless loops of "The Little Drummer Boy," try turning on the radio for a musical change. But if "The Lion Sleeps Tonight" comes on, it’s time for a new strategy. Getting involved in an attention-grabbing activity, from reading to gardening to playing a sport, may, at least temporarily, reset your compulsive brain.