The right inferior frontal gyrus processes nested non-local dependencies in music

Vincent K M Cheung,Angela D Friederici,Lars Meyer,Stefan Koelsch

doi:10.1038/s41598-018-22144-9

Vincent K M Cheung, Angela D Friederici + Show 2 more

Open Access

https://doi.org/10.1038/s41598-018-22144-9

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Abstract

Complex auditory sequences known as music have often been described as hierarchically structured. This permits the existence of non-local dependencies, which relate elements of a sequence beyond their temporal sequential order. Previous studies in music have reported differential activity in the inferior frontal gyrus (IFG) when comparing regular and irregular chord-transitions based on theories in Western tonal harmony. However, it is unclear if the observed activity reflects the interpretation of hierarchical structure as the effects are confounded by local irregularity. Using functional magnetic resonance imaging (fMRI), we found that violations to non-local dependencies in nested sequences of three-tone musical motifs in musicians elicited increased activity in the right IFG. This is in contrast to similar studies in language which typically report the left IFG in processing grammatical syntax. Effects of increasing auditory working demands are moreover reflected by distributed activity in frontal and parietal regions. Our study therefore demonstrates the role of the right IFG in processing non-local dependencies in music, and suggests that hierarchical processing in different cognitive domains relies on similar mechanisms that are subserved by domain-selective neuronal subpopulations.

Highlights

Complex auditory sequences known as music exist in all human cultures[1], and elements in many musical styles are hierarchically structured[2,3]
For the main effect of GRAMMATICALITY (UNGRAMMATICAL > GRAMMATICAL), we found a cluster of increased BOLD response with maxima in the right inferior frontal gyrus (IFG; pars opercularis, triangularis, and orbitalis), right middle frontal gyrus, and right anterior insular cortex (AIC)
We identified clusters in the pre-supplementary motor area, right dorsal premotor cortex, and left anterior insular cortex (AIC)

Summary

Introduction

Complex auditory sequences known as music exist in all human cultures[1], and elements in many musical styles are hierarchically structured[2,3]. Previous studies on processing hierarchical structures in music argued that humans can differentiate between auditory tone sequences generated according to a hierarchical recursive rule and an iterative rule[12], show priming effects in integrating harmonic contextual information[13,14], and discriminate between grammatical and ungrammatical transformations in serialist music[15,16]. Activity in the inferior frontal gyrus (IFG) was suggested to process hierarchical structure in music, given that language studies have implicated the left IFG – the pars opercularis – in syntactic reordering and embedding[28,29,30,31]. We manipulated the level of embedding (that is, the number of nested dependencies in a sequence) to dissociate the processing of nested dependencies in music from the effects of increasing working memory demands on processing these dependencies, and to ensure that the observed responses in resolving the nested dependencies generalised to different levels

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