Interpersonal frontopolar neural synchronization in group communication: An exploration toward fNIRS hyperscanning of natural interactions

Abstract

Research of interpersonal neural synchronization (INS) using functional near-infrared spectroscopy (fNIRS) hyperscanning is an expanding nascent field. This field still requires the accumulation of findings and establishment of analytic standards. In this study, we therefore intend to extend fNIRS-based INS research in three directions: (1) verifying the enhancement of frontopolar INS by natural and unstructured verbal communication involving more than two individuals; (2) examining timescale dependence of the INS modulation; and (3) evaluating the effects of artifact reduction methods in capturing INS. We conducted an fNIRS hyperscanning study while 12 groups of four subjects were engaged in cooperative verbal communication. Corresponding to the three objectives, our analyses of the data (1) confirmed communication-enhanced frontopolar INS, as expected from the region's roles in social communication; (2) revealed the timescale dependency in the INS modulation, suggesting the merit of evaluating INS in fine timescale bins; and (3) determined that removal of the skin blood flow component engenders substantial improvement in sensitivity to communication-enhanced INS and segregation from artifactual synchronization, and that caution for artifact reduction preprocessing is needed to avoid excessive removal of the neural fluctuation component. Accordingly, this study provides a prospective technical basis for future hyperscanning studies during daily communicative activities.

Steady Beat Sound Facilitates both Coordinated Group Walking and Inter-Subject Neural Synchrony

“…The button-press task shed light on the understanding of INS in the prefrontal region but the task setting is close to a laboratory experiment. Extending the previous findings into more real-life oriented social interaction, several studies showed connection between verbal communication and INS (Jiang et al, 2012, 2015; Nozawa et al, 2016). On the other hand, a previous study showed relationship between physical coordination (i.e., non-verbal interaction) and INS (Holper et al, 2012).…”

“…We used a wireless, portable, and ultra-small NIRS system ( Figure 1A ; Nozawa et al, 2016), which measures changes in the total hemoglobin (tHb) concentration with a light source of single wavelength at 810 nm. The sampling frequency of the device is 10 Hz.…”

“…The optical system comprises one light emitter and two light detectors; the emitter is 1 and 3 cm distant from the two detectors ( Figure 1B ); this is to enable our NIRS to create cerebrally unique responses by regressing out the nearby detector’s signals (1 cm) from that of the far detector (3 cm) (Saager et al, 2011). For recording, three optodes were placed over the subjects’ foreheads according to our previous implementation (Nozawa et al, 2016); these optodes approximately covered the center between FP1 and FP2 in the international 10–20 system, which correspond to the medial part of the frontal pole (Okamoto et al, 2004; Tsuzuki et al, 2007). Each subject’s hair under the optodes was carefully pushed off their foreheads.…”

“…Because WTC can show the local correlation between two time series for each frequency, it has been used in many fNIRS studies (Cui et al, 2012; Dommer et al, 2012; Holper et al, 2012; Jiang et al, 2012, 2015; Nozawa et al, 2016). We used a WTC Matlab package (Grinsted et al, 2004), which is provided on the authors’ website 2 .…”

“…We expected stepping did not show a significant difference of INS between presence and absence of the steady beat sound. To measure frontopolar activity, we used ultra-small NIRS ( Figure 1 ; Nozawa et al, 2016) which has many advantages: multi-brain measurement, wireless, no limits for natural movement, and measurement of skin blood flow. To estimate INS, we used wavelet transform coherence (WTC) (Torrence and Compo, 1998; Grinsted et al, 2004).…”