YUTO KURIHARA PERSONAL WEBSITE

RESEARCH

Interpersonal coordination and inter-brain synchrony

When we move in time with someone else, we adjust our movements in response to each other. This project aims to capture the inter-individual neural dynamics that emerge from interaction by measuring both people’s brain activity at the same time.

Keywords
Social interaction, Interpersonal coordination, Hyperscanning, Inter-brain synchrony

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Overview

Inter-brain EEG synchrony during coordinated tapping

When we act in rhythm with another person, we predict their movements and adjust our own. To explore the mechanisms supporting this interpersonal coordination, we focused on synchrony between the two participants’ brain activity (Kurihara et al., 2022, Scientific Reports).

In this study, we used hyperscanning, a method for simultaneously recording brain activity from multiple people. We recorded EEG from two participants performing alternating finger tapping and examined how coordination stability related to inter-brain synchrony (Figure 1).

An illustration of participant A at the back left and participant B at the front right, each labeled beside their EEG cap, seated with one hand on a mouse and the other resting on a thigh. A callout labeled “EEG headset” points to the head-mounted device.
Right index finger: left click
Right index finger: right click

1. Listen to the reference tempo

Remember the tempo of eight reference beats.

2. Take turns tapping

ABABABAB

After the reference stops, maintain the remembered tempo while listening to each other’s taps.

Figure 1. Alternating tapping with simultaneous EEG recording EEG is recorded from both participants as they take turns tapping, guided by the sounds of their taps. The sequence illustrates a prescribed-tempo condition. Adapted from Kurihara et al. (2022).

The results showed that, during fast alternating tapping, pairs with less stable coordination had stronger theta-band synchrony between one participant’s left-temporal region and the other’s central region (Figure 2). Instability was measured as the standard deviation of relative phase (SDRP). This positive association suggests that inter-brain synchrony may relate to the demands of adjusting movements to a partner.

A single figure combining the positive association between coordination instability (SDRP) and theta-band inter-brain synchrony with the corresponding left-temporal and central brain regions.
Figure 2. Coordination instability and theta-band inter-brain synchrony Redrawn from the original point positions, regression line and confidence band. The brain illustrations show the corresponding regions schematically. Adapted from Kurihara et al. (2022).

We also examined the interpersonal relationship between the two people coordinating their movements (Kurihara et al., 2024, Scientific Reports). We compared stranger and acquaintance pairs using networks that combine within- and between-brain synchrony (Figure 3). Stranger pairs showed higher local efficiency in the theta-band network, indicating more efficient connections among neighboring nodes. These findings suggest that network structure may reflect the relationship between the people coordinating their movements.

Stranger pair

A representative network from a stranger pair, with dense connections between the two participants’ electrodes.

Acquaintance pair

A representative network from an acquaintance pair, with sparser connections than the stranger-pair example.
Figure 3. Representative brain networks in stranger and acquaintance pairs Nodes represent EEG electrodes and edges represent synchrony-based functional connections. Redrawn from the published adjacency matrices and original electrode positions. Adapted from Kurihara et al. (2024).

Together, these insights provide clues to understanding the mechanisms underlying the dynamics of inter-brain synchrony that emerge from interpersonal interaction. Successful coordination or a closer relationship does not necessarily entail stronger inter-brain synchrony. To understand these dynamics, it is necessary to consider the social context in which interaction takes place and the processes through which people predict each other’s actions within that context.

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