Have your friends ever called you a broken CD player because you were singing the same song again and again without even realizing it? You can now tell them that you have evidence of how we all are cognitively wired to do that, thanks to the study performed by scientist Nicolas Farrugia and his team. The phenomenon of ‘stuck song syndrome’ or ‘earworms’ has been previously identified as ‘Involuntary Musical Imagery’ (INMI), a form of cognition occurring spontaneously without any conscious effort. Farrugia and co-workers identified the parts of brain responsible for INMI through their study. The researchers stated “To the best of our knowledge, this study is the first to investigate the neural basis of INMI.”
44 healthy subjects ranging between ages 25 to 70 years, including both the genders participated in the research conducted at the Cambridge Medical Research Council’s Cognition and Brain Sciences Unit. 8 subjects also played one or more musical instruments. The analysis of INMI was carried out through self-reports given by the participants through specific questionnaires and correlating them with brain scans obtained through structural Magnetic Resonance Imaging (MRI). The main aspects of analysis were measurement of frequency of INMI episodes and evaluation of affective or self-reflective aspects such as negative emotions or disturbance evoked by INMI, its helpfulness, movement of subjects in time with reference to their INMI and whether it reflected their personal emotions. There were additional questions for avoiding a bias in case the participants had any kind of previous musical training.
In order to carry out the brain-behaviour analysis to study INMI, the brain morphology was measured using 2 parameters, namely, voxel-based morphometry (VBM) and cortical thickness. These measurements, when compared to the self reports indicated that INMI frequency was related to the thickness/gray matter volume of the cerebral cortex in the temporal, inferior frontal, parietal, parahippocampal and anterior cingulate areas.
It was observed that cortical thickness reduction in the right Heschl’s Gyrus (found in the area of primary auditory cortex) was related to more frequent INMI whereas an inverse relationship was established between the thickness of the right inferior frontal gyrus (rIFG) and INMI occurrence, i.e. greater the thickness, less frequent the INMI episodes. The underlying reason for this correlation was that Heschl’s Gyrus has been found to play a role in both auditory perception and voluntary musical imagery and IFG has been implicated in pitch memory (type of musical memory). Also, IFG can be activated by both auditory perception and imagery. The researchers also expressed the possibility that the unwanted INMI episodes might be getting suppressed through the inhibitory role of the IFG owing to greater cortical thickness.
The researchers also explained how phenomenon like self-generated thoughts (SGT) including day dreaming and mind wandering were also along the same lines as INMI. They arise from spontaneous activity in the ‘Default Mode Network’ (DMN) which consists of areas in the brain such as medial prefrontal cortex, the posterior cingulate cortex, the PHC and the ventral anterior cingulated cortex. These areas are activated when there is no specific task in focus.
The future scope of this research includes both structural and functional MRI to further understand the functional contribution of the frontotemporal pathway to involuntary forms of musical imagery. The researchers suggest that it can be done using the same subjects chosen for the current study by assigning them a psychological task supposedly related to INMI and analyzing brain-behaviour relationship.
Thus, this study reveals how a seemingly simple experience such as a song getting stuck in your head can be related to deeper brain networks in our gray matter including perception, emotions, memory and spontaneous thoughts.
The original paper can be accessed in Consciousness and Cognition.