Conducting Hyperscanning Experiments with Functional Near-Infrared Spectroscopy

Summary

The present protocol describes how to conduct fNIRS hyperscanning experiments and analyze brain-to-brain synchrony. Further, we discuss challenges and possible solutions.

Abstract

Concurrent brain recordings of two or more interacting persons, an approach termed hyperscanning, are gaining increasing importance for our understanding of the neurobiological underpinnings of social interactions, and possibly interpersonal relationships. Functional near-infrared spectroscopy (fNIRS) is well suited for conducting hyperscanning experiments because it measures local hemodynamic effects with a high sampling rate and, importantly, it can be applied in natural settings, not requiring strict motion restrictions. In this article, we present a protocol for conducting fNIRS hyperscanning experiments with parent-child dyads and for analyzing brain-to-brain synchrony. Furthermore, we discuss critical issues and future directions, regarding the experimental design, spatial registration of the fNIRS channels, physiological influences and data analysis methods. The described protocol is not specific to parent-child dyads, but can be applied to a variety of different dyadic constellations, such as adult strangers, romantic partners or siblings. To conclude, fNIRS hyperscanning has the potential to yield new insights into the dynamics of the ongoing social interaction, which possibly go beyond what can be studied by examining the activities of individual brains.

Introduction

In recent years, neuroscientists have started to study social interactions by recording the brain activities of two or more persons simultaneously, an approach termed hyperscanning¹. This technique opens new opportunities to elucidate the neurobiological mechanisms underlying these interactions. To fully understand social interactions, it may not be sufficient to study single brains in isolation but rather the joint activities of brains of interacting persons². Using different neuroimaging techniques, hyperscanning studies have shown that brain activities of interacting persons or groups synchronize, e.g., while....

Protocol

Prior to participation, all parents / children provided informed consent / assent. The study was approved by the ethics committee of the Medical Faculty of RWTH Aachen University.

1. Preparation before the Participant Arrives

1. Prepare NIRS caps.
   1. Choose the cap sizes the same size or slightly larger than the participant’s head circumference.
   2. Cut 15 holes with a diameter of approximately 15 mm each, arranged in a horizontal 3x5 grid, into the forehead area of each of 2 raw EEG caps (see Table of Materials). Make sure that the holes are spaced 30 mm from each other in any direction, that....

Results

Representative data of one parent-child dyad during the cooperative condition are shown in Figure 1. The cooperative task consists of three 30 s rest blocks and two task blocks, with 20 trials each, presented in alternating order. In each trial, participants have to react as simultaneously as possible to a signal to earn a point¹¹.

Discussion

In this protocol, we show how to conduct fNIRS hyperscanning experiments and one possible way to analyze brain-to-brain synchrony, measuring concentration changes of oxy-Hb and deoxy-Hb at frontal brain regions of two subjects simultaneously. FNIRS hyperscanning is relatively easy to apply: a single NIRS device is sufficient to measure brain activities of both subjects by splitting the optodes between them. Thus, no synchronization between different devices is necessary¹. Moreover, since fNIRS doe.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
NIRS measurement system with probe sets and probe holder grids	Hitachi Medical Corporation, Tokyo, Japan	ETG-4000 Optical Topography System	The current study protocol requires an optional second adult probe set for 52 channels of measurement in total as well as two 3x5 probe holder grids.
raw EEG caps	EASYCAP GmbH, Herrsching, Germany	C-SCMS-56; C-SCMS-58	Caps must be provided with holes for NIRS probes by the experimenter. Choose cap size the same size or slightly larger than participant's head circumference.
Technical computing software	The MathWorks, Inc., Natick, MA	MATLAB R2014a (or later versions)	Serves as base for Psychophysics Toolbox extensions (stimulus presentation), SPM for fNIRS toolbox  (fNIRS data analysis), and ASToolbox (WTC computation).