Hearing just a few seconds of a song on the radio is enough for it to become stuck in your head for several hours. We’ve all experienced it at some point: that tune that keeps repeating in your mind, creating a rather unpleasant sensation for yourself and for your neighbors who can no longer stand you whistling the same tune over and over again. But where does this phenomenon come from? An imaging study reveals we don't all show the same patterns in response to this phenomenon.

At Goldsmiths, University of London, Dr. Nicolas Farrugia and his colleagues at the Music, Mind and Brain group study the cognitive and neural bases of listening to and playing music. They are particularly interested in the mechanisms of "earworm," a charming expression used to describe a song or melody that gets "stuck in your head." In scientific jargon, this phenomenon is known as “involuntary musical imagery” or INMI.

Thanks to this new research, the scientists discovered that this ability, if we can call it that, is linked to the thickness of the cerebral cortex (outer layer of the brain) in four key regions: the right frontal cortex, the temporal cortex, the cingulate cortex, and the upper angular gyrus. To observe this, the researchers questioned 44 volunteers about their experience with the phenomenon: how often they experienced it and whether it was associated with positive or negative emotions. These results were then compared with the subjects’ brain images from an MRI. The researchers thus determined that the greater the frequency of earworms, the thinner the cortex in the four regions mentioned earlier. These four regions have been shown to be involved in the perception of musical imagery and daydreaming.

“Earworms are extremely common, and appear spontaneously and without conscious control in the same way we might find ourselves daydreaming. Episodes are usually pleasant but can be quite disturbing,” says Dr. Farrugia. He adds "Our results link several aspects of the earworm experience with variations in cortical structure, providing evidence that the structure of fronto-temporal, cingulate and parahippocampal areas of the brain contribute to both the occurrence, and how people evaluate, the spontaneous internal experience of music."

The emotions related to these events are also associated with anatomical features, the unpleasant emotions being correlated with the volume of gray matter in the right temporo-polar cortex, while the pleasant emotions were associated with the parahippocampal cortex.