We’re exposed to music a lot in our daily lives, whether that’s through listening to the radio or our mp3 players, wandering around shops or people humming tunes in the street. And then one song gets stuck in our heads. It relentlessly pops back into our minds without warning, without a trigger, and we can’t help but start singing to ourselves.
This phenomenon, called involuntary musical imagery (INMI), or more colloquially “earworms,” is a common experience, but people with certain personality traits such as neuroticism may experience it more so than others. While this much was known, its neural basis was a mystery, but a new study has finally offered us some insight. According to the findings, its frequency seems to be linked to the thickness of brain regions involved in musical imagery, or the ability to imagine absent sounds. Furthermore, its occurrence and processing seems to be associated with areas involved in emotions and memory.
While some of you may think this is a trivial subject to spend time over, neuroscientists are interested in it not only because it’s omnipresent and can be complex, but also because it can boost our mood and emotions, much like actually listening to music. Additionally, around 40% of our daily thoughts are not under conscious voluntary control, and INMI is one of the most commonly reported forms of such spontaneous cognition.
For the study, researchers enrolled 44 healthy male and female participants ranging in age from 25 to 70. None of the volunteers had a history of neurological damage or hearing loss, and none were expert musicians. After completing a survey about their personal INMI experiences, including frequency and whether it can help with everyday activities, and their engagement with music so that differences in musical backgrounds could be controlled for, the researchers imaged their brains using an MRI machine. In particular, they were looking for morphological differences, such as greater volumes of brain tissue, which were associated with INMI.
As described in Consciousness and Cognition, they found a correlation between INMI frequency and cerebral cortex (cortical) thickness in two brain regions: the right Heschl’s gyrus (HG) and the right inferior frontal gyrus (IFG). Interestingly, the former has previously been linked with auditory perception, or how our brain interprets the sounds we hear, and voluntary musical imagery, the conscious version of INMI. The latter, on the other hand, is thought to be involved in our memory of pitch.
Surprisingly, they actually found that people who displayed reduced thickness in the right HG tended to experience INMI more frequently, which doesn’t fit in with research in which musical experts tended to have thicker cortices than non-experts. A negative correlation was also observed for the right IFG, but this makes sense because this brain region plays inhibitory roles in the brain and thus may reduce spontaneous activity in other areas. So if the area is reduced in thickness, then its inhibitory action may also be reduced, thus increasing INMI frequency.
Finally, the researchers also found a relationship between how useful individuals considered INMI to helping them get on with daily activities and the volume of brain tissue in a region critical for memory formation, called the parahippocampal cortex. All in all, the researchers conclude that “INMI is a common internal experience recruiting brain networks involved in perception, emotions, memory and spontaneous thoughts.”