Q: Why do I find some of the melodic themes 'playing' in my mind for several days after a concert? A: A catchy tune, whether classical or pop, is so well known for staying in the brain that the effect has long been exploited for advertising jingles, and there have been efforts to define what makes a melody 'sticky.' But a hard-to-shake melody can be a burden rather than a welcome souvenir, turning into what is sometimes called an earworm, and the reasons are not definitely known. The mental pathways for music are complex, sometimes including not only auditory areas but also the visual cortex of the brain. Recent research suggests that musical perception is entwined with primitive parts of the brain and that it can influence emotions through the limbic system. How a melody becomes an earworm, however, is unclear. A 2001 survey by James J. Kellaris of the University of Cincinnati, a consumer psychologist, found that 'music characterized by simplicity, repetitiveness and incongruity with listeners' expectations is most likely to become 'stuck.'' Up to 98 percent of people will experience a sticky tune, his study suggested, and some people, like musicians, women and the worry-prone, are more susceptible than others. The causes may be psychological or even physical, tied to sound frequencies that resonate in the body. After further research, Kellaris theorized that one way to scratch what he called a 'cognitive itch' is to sing the mental tune aloud. 