It’s a well-known phenomenon in media land that once you contributed to a TV item on a compelling —general interest— question, people will return to you with the same question over and over again, and, basically, wanting you to redo the same answer :-)
It happened to me a few years ago when I was asked to contribute to a Dutch TV item on the question why some melodies stick in your mind. My first answer was: we do not know. Since, if we knew, an ‘earworm’-generating computer program would exist that can generate melodies that are guaranteed to stick in people’s mind for days. In this particular case however, I’m sure nobody would mind. Unfortunately, now —four years later— still little is understood of the phenomenon. [And yes, again on Dutch TV]
What we do know —mainly from questionnaire-style research— is that most people suffer from the ‘earworm’ phenomenon (also referred to as brainworm, cognitive itch, or musical imagery repetition), females slightly more than males. And that the tunes that spontaneously pop-up in one’s mind are generally not the most striking compositions. Actually, they are commonly reported as being simply irritating (see examples on link below).
Why does this happen? And what does it tells us about our cognition? And why does it happen with music, and significantly less with text or images? What is in the musical structure of that particular fragment that makes it spontaneously pop-up from memory? PhD-students in cognitive science looking for an exciting relatively unexplored topic in music (neuro)cognition, jump on it!
Dutch webpage on this topic.