Electroencephalographic power spectrum and intersubject correlation on acoustic stimulation with modes of Indian music: a randomized controlled trial

Background Music not just entertains an individual but causes changes in the frequency spectrum of the brain waves and cognition that are recognizable using signals obtained through electroencephalography (EEG). EEG studies on the effect of passive listening to music have predominantly used multi-instrumental western classical music as an acoustic stimulus with very few analyzing solo instrumental Indian music, and thus in the current study Indian modes (Hindustani ragas) were used. The study aimed to investigate overall power spectral changes on EEG and specifically, those changes that show high inter-subject correlation (ISC) on passive listening to three different Indian modes as acoustic intervention, in comparison to control stimuli, heard for 10 minutes. Material & Methods A randomized control triple-blind trial with 4 groups (three music intervention groups and a control group; n=35 each) was conducted while undergoing EEG recording. The music intervention groups listened to 10-minute audio of one of the three different modes (namely raga Miyan ki Todi, raga Malkauns, and raga Puriya), while the control group received predominant silence with few natural sounds interspersed. EEG data before, during, and after acoustic interventions were first evaluated for electrode-level power changes in standard spectral bands (delta, theta, alpha, beta1, beta2, and gamma). To understand spectral power changes more specific to music listening, a novel component-level analysis was also done, where the raw spectral data were grouped into the three most prominent components (C1, C2 & C3) based on spatiospectral consistency across subjects (correlated component analysis or CorrCA) and their ISC scores were also computed. For statistical analysis, we applied a hierarchical general linear model with cluster statistics to the electrode-level data and robust ANOVA with post hoc tests to the component-level data. Results In electrode level analysis, the group listening to raga Malkauns showed a significant increase in gamma power in the left frontal regions during the intervention. While the group listening to raga Puriya showed a right frontoparietal decrease in delta power, raga Miyan ki Todi showed a frontal increase in beta1 power after the intervention. In component-level analysis, C1 was globally distributed low-frequency activity, C2 was posteriorly dominant alpha-beta1 activity, and C3 was peripherally dominant broad-band activity, consistent between groups. Besides agreement with electrode-level findings, the most prominent component-level finding was a decrease in C1 power and an increase in C2 power shown by raga Malkauns (strong both during and after intervention) and raga Miyan ki Todi (strong during and weak after intervention), whereas raga Puriya showed only a weak decrease in C1 (after intervention), compared to control group. ISC scores were comparable between groups, except for raga Puriya, which showed a marginal drop for C3 after the intervention. Conclusions Reduction in globally distributed low-frequency activity and increase in posterior dominant alpha-beta1 activity may be characteristic of passive listening to relaxing Indian modes, which may persist even after the listening period. Among the modes, raga Malkauns showed this effect most prominently, followed by raga Miyan ki Todi and least by raga Puriya. As the increase in posterior alpha and low beta power is associated with default mode network (DMN) activity and a decrease in delta power with positive emotional memory, the spectral pattern we observed may indicate observing positive autobiographical memory while listening to musical scales and thereby contributing to a relaxing experience. Further studies that also include phenomenological reports are highly recommended to be taken up to support these findings, and thus build a scientific foundation for the use of Indian music in medicine. Graphical Abstract Impact Statement In this manuscript on EEG power spectral changes, correlated component analysis, and Intersubject correlation, we found a reduction in globally distributed low-frequency activity and an increase in posterior dominant alpha-beta1 activity during listening to Indian modes of music, in comparison to the control group. Mode-specific changes in correlated components, indicating default mode network activity and probable activation of autobiographical memories were observed.