The role of functional and structural interhemispheric auditory connectivity for language lateralization - A combined EEG and DTI study

Saskia Steinmann,Götz Thomalla,Gregor Leicht,Rom Amselberg,Bastian Cheng,Andreas K Engel,Christoph Mulert

doi:10.1038/s41598-018-33586-6

Saskia Steinmann, Götz Thomalla + Show 5 more

Open Access

https://doi.org/10.1038/s41598-018-33586-6

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Abstract

Interhemispheric connectivity between auditory areas is highly relevant for normal auditory perception and alterations are a major factor for the development of auditory verbal hallucinations. Surprisingly, there is no combined EEG-DTI study directly addressing the role of functional and structural connectivity in the same group of subjects. Accordingly, nothing is known about the relationship between functional connectivity such as gamma-band synchrony, structural integrity of the interhemispheric auditory pathways (IAPs) and language lateralization as well as whether the gamma-band synchrony is configured on the backbone of IAPs. By applying multimodal imaging of 64-channel EEG and DTI tractography, we investigated in 27 healthy volunteers the functional gamma-band synchrony between either bilateral primary or secondary auditory cortices from eLORETA source-estimation during dichotic listening, as well as the correspondent IAPs from which fractional anisotropy (FA) values were extracted. Correlation and regression analyses revealed highest values for gamma-band synchrony, followed by FA for secondary auditory cortices, which were both significantly related to a reduced language lateralization. There was no such association between the white-matter microstructure and gamma-band synchrony, suggesting that structural connectivity might also be relevant for other (minor) aspects of information transfer in addition to gamma-band synchrony, which are not detected in the present coupling analyses. The combination of multimodal EEG-DTI imaging provides converging evidence of neural correlates by showing that both stronger pathways and increased gamma-band synchrony within one cohort of subjects are related to a reduced leftward-lateralization for language.

Highlights

Interhemispheric connectivity between auditory areas is highly relevant for normal auditory perception and alterations are a major factor for the development of auditory verbal hallucinations
We combined EEG measured functional gamma-band synchrony, Diffusion Tensor Imaging (DTI) probabilistic tractography of the interhemispheric auditory pathway (IAPs) and dichotic listening performance of 27 healthy volunteers to investigate the role of this white-matter pathway in coordinating gamma-band synchrony that is required for conscious auditory perception of left ear (LE) syllables
To the best of our knowledge, this is the first multimodal study combining DTI and EEG demonstrating that stronger pathways and increased gamma-band synchrony within one cohort of subjects are related to a reduced leftward-lateralization for language

Summary

Introduction

Interhemispheric connectivity between auditory areas is highly relevant for normal auditory perception and alterations are a major factor for the development of auditory verbal hallucinations. Correlation and regression analyses revealed highest values for gamma-band synchrony, followed by FA for secondary auditory cortices, which were both significantly related to a reduced language lateralization There was no such association between the white-matter microstructure and gamma-band synchrony, suggesting that structural connectivity might be relevant for other (minor) aspects of information transfer in addition to gamma-band synchrony, which are not detected in the present coupling analyses. This study revealed a huge interindividual variability in callosal topography linking homolog pSTG, emphasizing the functional relevance of interindividual white-matter differences These findings indicate that stronger IAPs as well as increased gamma-band synchronization between homolog pSTG are both contributing to conscious perception of LE syllables. It was hypothesized that a reduced left lateralization for language is related to (1) structural integrity measured by FA and, (2) increased functional gamma-band synchrony between homolog auditory cortices, and further, that (3) the magnitude of the interhemispheric gamma-band synchrony is related to structure of the IAPs

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