Phase synchrony analysis of EEG during music perception reveals changes in functional connectivity due to musical expertise

Differences in functional and topographical connectivity patterns between two groups, musicians and non-musicians, during attentively listening to three different pieces of music and to a text of neutral content, were presented by means of EEG phase synchrony analysis in five standard frequency bands: delta (<4 Hz), theta (4-8 Hz), alpha (8-13 Hz), beta (13-30 Hz), and gamma (>30 Hz). The degree of phase synchrony or phase coherence between EEG signals was measured by a recently developed index, which is more suitable than classical indices, like correlation or coherence, when dealing with nonlinear and nonstationary signals like EEG. Comparing the music listening task to rest or control condition, musicians showed increase in phase synchrony over distributed cortical areas, both near and distant, in delta, and most conspicuously in gamma frequency band, whereas non-musicians showed enhancement only in delta band. Further, the degree of phase synchrony in musicians was reduced during listening to text as compared to listening to music. Comparing the two groups during the listening tasks, the clear-cut difference was found in gamma band phase synchrony, which was significantly stronger in musicians while listening to every chosen piece of music, yet no large difference between these two groups was found while listening to the chosen text. Musicians also showed stronger higher order inter-frequency phase synchrony between delta band oscillations in anterior regions and gamma band oscillations in posterior regions. In addition, consistent left hemispheric dominance, in terms of the strength of phase synchrony, was observed in musicians while listening to music, whereas right hemispheric dominance was observed in non-musicians. These results suggest that professional training in music is able to elicit context-sensitive functional connectivity between multiple cortical regions resulting in different listening strategies to music.