Brain Regions Underlying Music Improvisation and its Performance Enhancement by Improving Processing of Rhythmic Microtiming

概要

This thesis consists of two parts, 1. explores neural activity underlying creative processes through the investigation of music improvisation, and 2. explores the possibility to enhance the music improvisation performance by improving rhythm perception through behavioral feedback training during neural modulation using a multi-channel anodal transcranial direct current stimulation (tDCS) to the left dorsal premotor cortex. For Part.1, fourteen guitar players with a high level of improvisation skill participated in the experiment. EEG data was measured continuously throughout the experiment. Source localization was carried out using standardized low resolution brain electromagnetic tomography (sLORETA) for the brain-related activity extracted by Band pass filtering, Artifact Subspace Reconstruction, and Independent Component Analysis. Greater activity for improvisation over scale was found in multiple frequency bands (theta, alpha, and beta), and machine-learning using Common Spatial Patterns (CSP) for EEG feature extraction attained a mean of over 75% classification performance for improvisation vs. scale conditions across participants. These results suggest that improvisation was mediated by processes involved in coordinating planned sequences of movement that are modulated in response to ongoing environmental context through monitoring and feedback of sensory states in relation to internal plans and goals.

For Part.2, the goal of this study was to determine the influence of the left dorsal premotor cortex (dPMC), which is thought to be involved with rhythmic timing perception and perceptual motor control, for musical improvisation by using behavioral feedback training to improve timing precision combined with a multi-channel tDCS targeting the left dPMC. Multi-channel tDCS has better targeting of a specific brain region over just using the standard bipolar anodal - cathodal setup. The experiment was designed to investigate the change in improvisation performance before and after a training session in which tDCS (two types: 1. anodal, 2. sham) is used to modulate dPMC during a rhythm processing training task (two tasks: 1. On the beat task, 2. Before the beat task). Training Before the beat task was thought to be a positive effect on the evaluation of music improvisation because it would help to create microtiming deviations (MTDs) effects, which states that the little discrepancies between rhythm section and soloists are crucial to create a tensional listening experience. For the evaluation of the participants’ improvisation tasks, Consensual Assessment Technique (CAT) was used with high interrater reliability (intraclass correlation coefficient with average random raters > 0.9, p < 0.01, N=3). The results revealed that the group with training with the Before the beat task statistically significantly improved their CAT scores over those training with the On the beat task. However, modulating left dPMC by multi-channel anodal tDCS had no statistically significant effect on the CAT scores over sham tDCS.