New Framework for Understanding Cross-Brain Coherence in Functional Near-Infrared Spectroscopy (fNIRS) Hyperscanning Studies

Summary

Wavelet transform coherence (WTC) is a common methodology for assessing the coupling between signals that is used in functional near-infrared spectroscopy (fNIRS) hyperscanning studies. A toolbox for assessing the directionality of the signal interaction is presented in this work.

Abstract

Despite the growing body of functional near-infrared spectroscopy (fNIRS) hyperscanning studies, the assessment of coupling between two neural signals using wavelet transform coherence (WTC) seems to ignore the directionality of the interaction. The field is currently lacking a framework that allows researchers to determine whether a high coherence value obtained using a WTC function reflects in-phase synchronization (i.e., neural activation is seen in both members of the dyad at the same time), lagged synchronization (i.e., neural activation is seen in one member of the dyad prior to the other member), or anti-phase synchronization (i.e., neural activation is increased in one member of the dyad and decreased in the other). To address this need, a complementary and more sensitive approach for analyzing the phase coherence of two neural signals is proposed in this work. The toolbox allows investigators to estimate the coupling directionality by classifying the phase angle values obtained using traditional WTC into in-phase synchronization, lagged synchronization, and anti-phase synchronization. The toolbox also allows researchers to assess how the dynamics of interactions develop and change throughout the task. Using this novel WTC approach and the toolbox will advance our understanding of complex social interactions through their uses in fNIRS hyperscanning studies.

Introduction

In recent years, there has been a shift in the types of studies conducted to understand the neural bases of social behavior^1,2. Traditionally, studies in social neuroscience have focused on neural activation in one isolated brain during a socially relevant task. However, advances in neuroimaging technology now allow for the examination of neural activation in the brains of one or more individuals during social interaction as it occurs in "real-life" settings³. In "real-life" settings, individuals are able to move freely, and patterns of brain activation are likely to cha....

Protocol

The study was conducted at Florida Atlantic University (FAU) and was approved by the FAU Institutional Review Board (IRB).

1. Using Homer3 software (Table of Materials) to perform the pre-processing of the fNIRS hyperscanning data

NOTE: Homer3 is a MATLAB application that analyzes fNIRS data to obtain estimates and maps of brain activation²⁹. Homer3 can be downloaded and installed from the following link (https://openfnirs.org/.......

Discussion

One of the most common methods used in fNIRS studies is wavelet transform coherence (WTC), which is a measure of the cross-correlation of two time series as a function of frequency and time¹⁰. WTC calculates the coherence and phase lag between two time series using correlational analyses (Supplementary File 1). FNIRS hyperscanning studies have used WTC to estimate IBS in many domains of functioning, including action monitoring¹², cooperative and competitive.......

Materials

Name	Company	Catalog Number	Comments
NIRScout	NIRx Medical Technologies, LLC	n.a.	8 sources, 8 detectors
MATLAB	The Mathworks, Inc.	Matlab 2022a	In this protocol, several toolboxes and buit in MATLAB functions were used: HOMER3 toolbox was used to convert Intensity to OD, to remove motion artifacts through its function hmrMotionCorrectWavelet with default parameters and to convert OD to Conc. Wavelet Toolbox was used to compute WTC.