Addressing arbitrary choices of frequency band of interest in fNIRS hyperscanning

Neuroimaging hyperscanning-the monitoring of brain activity of two or more persons simultaneously-has emerged as a popular tool to uncover the neural mechanisms of social interactions. The use of functional near-infrared spectroscopy (fNIRS)-a non-invasive, child-friendly technique tolerant of motion artifacts-has significantly advanced the research of social interactions. Despite its popularity, the field has yet to agree on best practices for quantifying inter-brain connections (IBC) during social interactions, including the frequency band of interest (FOI) for signal analysis. Various choices of FOIs, along with subject-level physiological differences or experimental design, may have contributed to inconsistent findings across prior studies. In this study, we reviewed various methods used and their corresponding FOI results in previous fNIRS hyperscanning research focused on the topics of cooperation. Additionally, we propose a new methodology to quantify FOI that aims to point to the origin of synchronization between brains. We tested the proposed method on three independent fNIRS hyperscanning datasets. The three datasets involved three different populations and three types of social interactions commonly studied in the literature. We examined the effect of sample sizes and data exclusion rates on the calculation of FOIs and statistical results. We offer a method for testing and adoption within the fNIRS community, aimed at eliminating arbitrary FOI selections and potentially enhancing the reproducibility of results in future fNIRS hyperscanning research.