Abstract
The present study investigates brain-to-brain coupling, defined as inter-subject correlations in the hemodynamic response, during natural verbal communication. We used functional near-infrared spectroscopy (fNIRS) to record brain activity of 3 speakers telling stories and 15 listeners comprehending audio recordings of these stories. Listeners’ brain activity was significantly correlated with speakers’ with a delay. This between-brain correlation disappeared when verbal communication failed. We further compared the fNIRS and functional Magnetic Resonance Imaging (fMRI) recordings of listeners comprehending the same story and found a significant relationship between the fNIRS oxygenated-hemoglobin concentration changes and the fMRI BOLD in brain areas associated with speech comprehension. This correlation between fNIRS and fMRI was only present when data from the same story were compared between the two modalities and vanished when data from different stories were compared; this cross-modality consistency further highlights the reliability of the spatiotemporal brain activation pattern as a measure of story comprehension. Our findings suggest that fNIRS can be used for investigating brain-to-brain coupling during verbal communication in natural settings.
Highlights
The present study investigates brain-to-brain coupling, defined as inter-subject correlations in the hemodynamic response, during natural verbal communication
Multiple brain areas have been identified to be involved with verbal communication using Positron Emission Tomography (PET) and functional Magnetic Resonance Imaging[1], whereas the timing of auditory processing was studied with the aid of Electroencephalogram (EEG) and Magnetoencephalogram (MEG)[2,3,4,5,6,7]
We identified the brain-to-brain coupling between a speaker telling an unrehearsed real-life story and a group of listeners listening to the story, with the aid of functional nearinfrared spectroscopy (fNIRS)
Summary
The present study investigates brain-to-brain coupling, defined as inter-subject correlations in the hemodynamic response, during natural verbal communication. Stephens et al investigated the alignment (correlation) of neural activity between speaker and listener during natural verbal communication using fMRI12. Higher coupling was found to be associated with better understanding of the story This neural coupling between speaker and listener was further supported by a recent EEG study in which the coordination between the brain activity of speakers and listeners was investigated with canonical correlation analysis[13]. Novel findings have been discovered using fMRI and EEG to address the aforementioned challenges, certain limitations of the two neuroimaging technologies have hindered the investigation of neural coupling during natural verbal communication. The localization of sources from the EEG signal requires higher-density recordings and additional computation to solve the inverse problem[16,17,18]
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