In a 2011 survey by Lassi Liikkanen, a Finnish cognitive scientist, more than 90 percent of respondents said they were bugged by an earworm at least once a week.

Kassel, Germany - It's a nice evening, the insects are chirping in the trees, you've got a good book in your hand and suddenly, out of nowhere, “Jingle Bells” pops into your head and won't go away.

Oh, what fun!

Almost everyone has had an attack of what Germans call an “earworm.”

In recent years musicologists, neurologists, physiologists and psychologists have all examined the phenomenon of a song or melody that keeps repeating in one's mind, also known by terms including “stuck song syndrome” and “involuntary musical imagery.”

In a 2011 survey by Lassi Liikkanen, a Finnish cognitive scientist, more than 90 percent of respondents said they were bugged by an earworm at least once a week.

Some people are more susceptible to them than others, “primarily those who have a lot to do with music, who make music themselves, listen to the radio a lot or have a large record collection,” said Jan Hemming, a professor of musicology at the University of Kassel.

Personality traits likely play a role as well, according to Eckhart Altenmueller, who treats sick musicians at a Hanover university.

“Sensitive people who generally have a low threshold for stimuli are particularly susceptible to earworms,” he said.

It is unclear how songs and melodies become stored for later re- and re-retrieval in a person's long-term memory.

Since earworms cannot be produced deliberately, their inception is difficult to observe with magnetic resonance imaging or electroencephalography.

To become lodged in one's long-term memory, the maddening music must fulfil certain criteria, however.

“In catchy tunes, there are no large leaps between notes and no complex rhythms,” Altenmueller said, adding that instrumental pieces rarely became earworms.

“Simple lyrics can be conducive (to earworms). By the same token, a song in a foreign language that you don't understand likely won't become an earworm.”

The number of times you have heard a certain song probably plays no role. What counts is an emotional connection with it.

“The effect occurs when someone associates strong feelings with a melody, usually positive but sometimes negative ones,” said Michael Deeg, an official in the German Association of Otorhinolaryngologists.

A hit tune released during a special summer holiday or your first love's favourite song are likely earworm candidates. Unwittingly stored in your long-term memory, they can pop into your mind at odd moments.

“This tends to happen in situations when the brain is idling,” Hemming said. In other words, during the low-attention state known as “mind-wandering,” for example when a person is cleaning house, jogging or waiting at a bus stop.

An association - a verbal cue, a place, a smell, a particular mood - can trigger the memory, hours or even years after the person has heard the song.

“The melody is activated in the form of short sequences or snippets,” typically between four and eight seconds in length, Altenmueller said. “For one person it's the beginning, for another a certain rhyme or the last line of the lyrics.”

The duration of an earworm experience is just as unpredictable as its occurrence.

Several techniques have been suggested to banish an earworm from one's mind. Some scientists advise listening to the entire earworm song to free the brain from the thrall of the repeating snippets. Deeg recommends listening to a different song.

“The earworm is stored in regions of the central nervous system responsible for hearing in general,” he said, noting that the brain was unable to “play back” the earworm while processing new acoustic signals.

But beware: This strategy could very well cause infection by another earworm.

Some earworm sufferers try to keep their mind from wandering.

“This can be done, for example, by concentrating on a pleasantly challenging activity with little connection to emotions,” Hemming said. Effective diversions include chess, intensive conversations and sudoku puzzles. - Sapa-Dpa