A catchy tune isn't always a good thing. If it contains an infectious chorus, even a song you dislike might refuse to leave your head. ("Achy Breaky Heart," anyone?) The choice of descriptors is not lost on Keith Duffy, a professor of rhetoric and composition at Penn State Schuylkill and a musician on the side. "Oddly enough," Duffy says, "this same rhetoric also describes communicable diseases."

There may be cognitive reasons behind a tune's appeal, he suggests. Referring to a study done at Dartmouth College last year, Duffy explains that "MRIs show that a catchy song makes the auditory part of the brain 'itch', and the only way the itch can be scratched is by listening to the song."

(Editor's note: The idea of a cognitive itch was first advanced by University of Cincinnati marketing professor James Kellaris in 2001.)

"Test subjects were played snippets of familiar songs that had segments removed. Participants said their brains filled in the gaps—in fact, they "heard" the removed parts of the songs in their heads," Duffy continues. "This was especially true in songs that had lyrics—as well as songs which evoked strong visual memories in participants."

If mentally repeating a song is the brain 'scratching', Paul Barsom wants to pin down exactly what causes that initial 'itch'.

"It's a pretty intangible thing," says Barsom, professor of music composition at Penn State. "If it wasn't, then everybody would be writing catchy songs." Certain kinds of musical gestures or combinations, he adds, seem to plug readily into our memory, like molecules coming together in a chemical reaction. "We will, we will, rock you is just easy to remember."

Barsom lists several factors that might cause a song to be catchy. "A certain familiarity—similarity to music one already knows—can play a role," he explains. "Unfamiliar music doesn't connect well. It's harder to own, especially on first listen." Picture a teen with an affinity for punk rock listening to his or her grandfather's Tchaikovsky collection—or vice versa.

Taking familiarity a step further, Barsom adds that a cultural connection between music and listener can make a tune more memorable. To listeners of a certain generation, for example, the music of the Beach Boys opened up a whole new world of summer and surfing. "Their connection to their audience made the music more appealing."

Repetition can also make a song hard to forget in two ways, Barsom says. "If you have a hook (a short catchy phrase or passage) in the song, and if that hook is repeated often, that could do it. You might only remember five seconds of the song—but sometimes that's enough." In addition, he notes, repeated radio play could force a song to become catchy. "You could hear a song 25 times a day. If it has a short refrain that everyone can remember, it will stick, even if it's terrible."

Lastly, a particularly appealing performance of the song may be enough to make it stick in your head. "Sometimes there's a certain electric thing that really carries a mediocre song, just the manner in which it is played. But who could possibly figure out what that is?"

Barsom concludes that there is no definite blueprint for constructing a catchy song. At best, most songwriters can only try out different melodies until one of them sounds like a keeper, a method which musician Duffy can identify with.

"I know when I am composing and recording music, certain chord or note progressions will evoke an emotion in me, in almost a primordial way. When this happens, I am compelled to explore that relationship further," he says.

For Duffy and Barsom, it seems, finding a formula for 'catchiness' is futile; instead, recognition is the key. If it's going to spread and stick, a tune must first infect the songwriter.

Keith Duffy, Ph.D., is an associate professor of rhetoric and composition at Penn State Schuylkill. He can be reached at wkd2@psu.edu. Paul Barsom, Ph.D., is an associate professor of music at Penn State. He can be reached at prb4@psu.edu.