Analysis of inter-brain synchrony in group-based electroencephalography to assess task-dependent interactions

Introduction: Social interaction and cooperative behavior are inherent and important aspects of daily life. Neuroscience research has demonstrated that neural activity synchronizes during cooperative group behavior. Hyperscanning, a method of simultaneously recording neural activity from two or more subjects, allows insight into the underpinnings of neural dynamics. Methods: This study involves a triadic 24-channel EEG hyperscanning experiment, using a cooperative card game to elicit group interaction and cognitive puzzle games as individual control tasks. The study was split into two separate experiments. Experiment One, where two groups repeatedly performed experimental blocks and Experiment Two where 10 individual groups participated in one block, where an adversary was randomly introduced to determine if negative social behavior changed neural synchrony. After removing artefactual contributions of muscle and eyeblink components and task duration discrepancies that may affect the group's synchrony, the neural correlation between subjects was examined via Inter-Subject Correlation (ISC). Linear mixed-effect models were used to assess the magnitude of differences in ISC, unadjusted, and adjusted trial-duration. Results: Similar neural synchrony levels were observed in the group members in Experiment One (unadjusted: cooperative ISC = 0.286 ± 0.013, individual ISC = 0.267 ± 0.02, baseline ISC = 0.219 ± 0.008, duration-adjusted: cooperative ISC = 0.225 ± 0.015, individual ISC = 0.278 ± 0.017, baseline ISC = 0.23 ± 0.007) and Experiment Two (unadjusted and duration-adjusted: cooperative ISC = 0.186 ± 0.009, individual ISC = 0.177 ± 0.01, baseline ISC = 0.157 ± 0.005). Discussion: While no statistically significant differences were found between cooperative and non-cooperative tasks, task-based synchrony was higher than resting state synchrony. Furthermore, significantly higher brain synchrony was observed in cooperative tasks when there were no adversaries present in the group. This study highlights the importance of analysis parameters like the analysis time window and task contrasts avoiding similarities in cognitive demands when evaluating brain synchronization in naturalistic environments for group-based interactions.