Name: how to calculate and validate inter-brain synchronization in a fnirs hyperscanning study
Uploaded: 2021-09-08T14:15:00
Description: Watch this Scientific Journal Video about How to Calculate and Validate Inter-brain Synchronization in a fNIRS Hyperscanning Study at JoVE.com

This research was supported by: National Natural Science Foundation of China (31872783, 31800951).

The protocol presented here was approved by the University Committee on Human Research Protection of East China Normal University.
1. Preparation for the experiment
<ol>
	<li>Participants
	<ol>
		<li>Recruit a group of undergraduate and graduate students with monetary compensation by the campus advertising.</li>
		<li>Ensure that the participants are right-handed and have normal or corrected-to-normal vision and hearing. Ensure that they have not studied music or have studied it for fewer th...

This protocol provides a step-by-step procedure to calculate and validate IBS, using the fNIRS hyperscanning approach to simultaneously collect two participants&#39; brain signals. Some critical issues involved in fNIRS data preprocessing, IBS calculation, statistics, and IBS validation are discussed below.
Data Preprocessing 
It is necessary to preprocess fNIRS data in hyperscanning studies to extract real signals from the possible noise (i.e., motion artifacts, systemic...

When people coordinate with others, their brains and bodies become a coupled unit through continuous mutual adaption. The coupling between brains can be represented by inter-brain synchronization (IBS) through the hyperscanning approach, which simultaneously records two or more individuals&#39; brain signals1. Indeed, a growing body of fNIRS/EEG hyperscanning studies has found IBS in various collaboration contexts, including finger tapping2, group walking3, playing drums4, guitar playing5, and singing/humming6. fNIRS is widely used for the research of IBS during social interaction, as it less restricts head/body motions in relatively natural settings (compared to fMRI/EEG)7.
The article presents a protocol for calculating IBS via wavelet transform coherence (WTC) method in an fNIRS hyperscanning study. WTC is a method for assessing the cross-correlation between two movement signals on the time-frequency plane and, therefore, can give more information than the traditional correlation analysis (e.g., Pearson correlation and cross-correlation), which is only in the time domain8. In addition, hemodynamic signals are transformed into wavelet components, which can effectively remove the low-frequency noise. Although WTC is time-consuming, it has been the most commonly used method of calculating IBS in action imitation9, cooperative behavior10, verbal communication11, decision making12, and interactive learning13.
The article also presents how to validate IBS with the permutation-based random paring of trials, conditions, and participants. The IBS in hyperscanning studies is always proposed to track online social interaction between individuals, while it can also be interpreted by other explanations, such as the stimulus similarity, motion similarity, or condition similarity14. Permutation test, also called randomization test, can be leveraged to test the above-mentioned null hypotheses through resampling the observed data15. By using permutation, it is useful to investigate whether the identified IBS is specific to interactive behavior, ranging from modulation of IBS within dyads to between groups of partners16.
The protocol described here details how to obtain brain signals via fNIRS technology, calculate IBS through the WTC method, and validate IBS by permutation testing in a hyperscanning study. This study aims to examine whether privileged IBS is elicited by music meters during social coordination. The brain signals were recorded in the frontal cortex, based on the location of the IBS in a previous finding1. The experimental task was originally developed by Konvalinka and her colleges17, in which participants were asked to tap their fingers with the auditory feedback from the partner or themselves after listening to the meter or non-meter stimuli.

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			<td>Computer</td>
			<td>Hewlett-Packard Development Company, L.P.</td>
			<td>HP S01-pF157mcn</td>
			<td></td>
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		<tr>
			<td>Earphone</td>
			<td>Royal Philips Electronics, Eindhoven, The Netherlands</td>
			<td>SHE2405BK/00</td>
			<td></td>
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			<td>EEG cap</td>
			<td>Compumedics Neuroscan, Charlotte, USA</td>
			<td>64-channel Quik-Cap</td>
			<td></td>
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			<td>E-Prime software</td>
			<td>Psychology Software Tools, Inc., Pittsburgh, USA</td>
			<td>E-Prime 3</td>
			<td></td>
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		<tr>
			<td>fNIRS system</td>
			<td>Hitachi Medical Corporation, Tokyo, Japan</td>
			<td>ETG-7100 Optical Topography System</td>
			<td></td>
		</tr>
		<tr>
			<td>MATLAB 2014b</td>
			<td>The MathWorks, Inc., Natick, MA</td>
			<td>MATLAB 2014b</td>
			<td></td>
		</tr>
		<tr>
			<td>MuseScore</td>
			<td>Musescore Company, Belgium</td>
			<td>MuseScore 3.6.2.548021803</td>
			<td></td>
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			<td>Swimming cap</td>
			<td>Decathlon Group, Villeneuve-d&#39;Ascq, France</td>
			<td>1681552</td>
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how to calculate and validate inter-brain synchronization in a fnirs hyperscanning study

The dynamics between coupled brains of individuals have been increasingly represented by inter-brain synchronization (IBS) when they coordinate with each other, mostly using simultaneous-recording signals of brains (namely hyperscanning) with fNIRS. In fNIRS hyperscanning studies, IBS has been commonly assessed through the wavelet transform coherence (WTC) method because of its advantage on expanding time series into time-frequency space where oscillations can be seen in a highly intuitive way. The observed IBS can be further validated via the permutation-based random pairing of the trial, partner, and condition. Here, a protocol is presented to describe how to obtain brain signals via fNIRS technology, calculate IBS through the WTC method, and validate IBS by permutation in a hyperscanning study. Further, we discuss the critical issues when using the above methods, including the choice of fNIRS signals, methods of data preprocessing, and optional parameters of computations.&#160;In summary, using the WTC method and permutation is a potentially standard pipeline for analyzing IBS in fNIRS hyperscanning studies, contributing to both the reproducibility and reliability of IBS.

The results showed that there was IBS at channel 5 in the meter coordination condition, whereas no IBS existed in other conditions (i.e., meter independence, non-meter coordination, non-meter independence; Figure 2A). At channel 5, the IBS in the meter coordination condition was significantly higher than the coherence values in the non-meter coordination and meter independence condition (Figure 2B). Channel 5 approximately belonged to the left dorsolateral prefr...

Watch this Scientific Journal Video about How to Calculate and Validate Inter-brain Synchronization in a fNIRS Hyperscanning Study at JoVE.com

How to Calculate and Validate Inter-brain Synchronization in a fNIRS Hyperscanning Study

The dynamics between coupled brains of individuals have been increasingly represented by inter-brain synchronization (IBS) when they coordinate with each ...

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