Imagine you spend the whole day with Old MacDonald stuck in your head. While it might not have been with this song in particular, we’ve all had the experience of having a song looping in our head that we can’t seem to get rid of. Researchers at Goldsmiths University studied the neuronal bases of this phenomenon, often called “earworm.” How does a melody become “sticky?”

More formally known as “Involuntary Musical Imagery” (INMI), earworm happens spontaneously and without our conscious control. This cognitive phenomenon is very widespread and is generally triggered by recent exposure to the song in question, but can also be influenced by our mood. For some, INMI can be a real nightmare, while others find it rather pleasant. Why this difference in experience? The study published in the review Consciousness and Cognition provides some answers.

In order to shed light on these individual differences, the researchers tried to better understand the neural basis of INMI. They asked 44 participants between the ages of 25 and 70 (23 women; 70% of subjects were between 20 and 40), to fill out an online questionnaire to evaluate how often INMI episodes occurred, how long they lasted and the emotions they solicited, and their effect on concentration. The data from the survey were then compared with measurements of the thickness of the cerebral cortex and the volume of gray matter, measured by structural MRI.

The results indicated that subjects who experience earworm the most often have a thinner cortical thickness in two areas of each cerebral hemisphere: the transverse temporal gyrus (used in sound perception and interpretation) and the inferior frontal gyrus (used in verbal memory processes). Moreover, the finding appears to be independent of cerebral aging as it is observed in the youngest participants as well (those under 40). Another surprising observation: the subjects that found INMI unpleasant had more gray matter in the right temporal lobe than those who found it enjoyable. This area is linked to hearing as well as emotional memory. Variations in gray matter volume were also seen in the parahippocampal gyrus (involved in memorization) in participants that found INMI to be helpful for concentrating or performing a specific task.

Thus, the very structure of the brain influences the frequency of INMI. As for knowing whether certain songs are more “at risk” than others, Nicolas Farrugia, study co-author, explains that songs vary widely between individuals. Finally, while not a miracle cure, if you’re looking for a trick for getting rid of your earworm, a study published by English researchers in April 2015 in The Quarterly Journal of Experimental Psychology suggests… chewing gum!