Inter-brain entrainment (IBE) during interoception. A multimodal EEG-fNIRS coherence-based hyperscanning approach

Human social interaction relies on the alignment of neural activity between individuals during collaborative tasks, yet the role of internal bodily awareness remains unclear. Prior research has shown that motor synchronization serves as a fundamental mechanism for establishing social bonds and facilitating group cohesion. Neuroimaging studies frequently utilize hyperscanning to observe these real-time interactions across multiple brains simultaneously. While Electroencephalogram (EEG) provides high temporal resolution, functional Near-Infrared Spectroscopy (fNIRS) offers superior spatial localization of hemodynamic responses. The integration of these two modalities allows for a more comprehensive understanding of the brain's response to social stimuli. Existing literature suggests that interoception, or the internal perception of bodily states, significantly modulates individual cognitive processing and emotional regulation. This absence of evidence motivated the current investigation into how interoceptive manipulation affects neural synchrony during shared motor activities.

This investigation evaluates the impact of interoceptive focus and shared intentionality on the neural coupling between interacting individuals. Researchers sought to determine if focusing on respiratory rhythms alters the strength of Inter-brain entrainment (IBE) during rhythmic motor tasks. The study addresses whether the presence of a clearly defined common goal enhances the synchronization of cortical oscillations and hemodynamic responses. Investigators designed the experiment to compare social conditions against non-social versions of the same motor synchronization exercise. The project also targets the development of a robust analysis pipeline for integrating multimodal neuroimaging data from dyads. By examining these variables, the team aimed to identify the specific cortical regions responsible for mediating joint action and internal awareness. The work clarifies how internal bodily attention interacts with external social objectives to shape the landscape of human neural connectivity.

The experimental design involved 13 dyads performing a motor synchronization task under varying cognitive and social conditions. Participants used a multimodal functional Near-Infrared Spectroscopy - Electroencephalogram (fNIRS-EEG) system to capture simultaneous brain activity. The electrophysiological component recorded cortical oscillations across delta, theta, and alpha frequency bands during the trials. Hemodynamic changes were monitored by measuring oxygenated hemoglobin (oxy-Hb) and deoxygenated hemoglobin (deoxy-Hb) levels throughout the cortex. The protocol included an interoceptive condition where subjects focused on their breath and a control condition with external focus. Researchers implemented two versions of the motor task to distinguish between collaborative efforts with a shared goal and individualistic performance. A novel statistical analysis pipeline was developed to calculate the coherence between functional connectivity signals within each interacting couple.

Data analysis revealed significant correlations between EEG delta, theta, and alpha bands and hemodynamic oxy-Hb levels in the left hemisphere. The interoceptive condition produced higher neural coupling in these frequency ranges compared to the control condition during motor tasks. Left anterior regions showed preferential activation when participants maintained internal attention to their respiration while synchronizing movements. Significant Inter-brain entrainment (IBE) correlations emerged in the delta and theta bands when a shared goal was explicitly presented. The collaborative version of the task elicited stronger neural alignment than the no-social version across the dyadic pairs. Hemodynamic responses in the left hemisphere demonstrated greater sensitivity to the experimental manipulations than those in the right hemisphere. The integrated EEG-fNIRS analysis successfully identified specific frequency-dependent patterns of coherence that traditional single-modality approaches might overlook.

These findings show that both interoceptive attention and joint intention significantly modulate the neural architecture of social interaction. The activation of left anterior regions suggests a specialized cortical network for integrating internal bodily signals with external social cues. Future research can utilize the proposed multimodal coherence pipeline to explore other complex social behaviors and psychiatric conditions. The study highlights the importance of considering internal physiological states when designing interventions for social or motor rehabilitation. Methodological advancements in EEG-fNIRS hyperscanning provide a more comprehensive view of the brain's electro-hemodynamic coupling during real-world tasks. Understanding how shared goals enhance Inter-brain entrainment (IBE) offers practical insights for optimizing teamwork and collaborative performance in various settings. The results confirm that the human brain prioritizes social and internal information through distinct but overlapping neural mechanisms.