Two-in-one: inter-brain hyperconnectivity during cooperation by simultaneous EEG-fNIRS recording

Hyperscanning is a quite recent paradigm in neuroscience which consists in the simultaneous recording of the cerebral activity of two or more subjects involved in interactive tasks. This measure allows to explore inter-personal brain mechanisms underlying and generated by social interactions, when participants are continuously modifying their own actions according to the partner’s ones. Previous studies showed that this mutual adaptation results in interactional brain synchrony to which all members contribute; accordingly, these mechanisms are involved only during interactive social relations and cannot be captured by conventional single-subject recordings. However, hyperscanning research recurred to either electrocortical or imaging techniques to explore the temporal dynamics or the brain networks involved in interactive behaviors but, to our knowledge, there are no previous attempts to acquire both measures jointly. Thus, the aim of the present study was to investigate the cognitive processes underlying the execution of joint cooperative actions performed by couples of subjects by means of a multi-method hyperscanning technique. We aimed at assessing to what extent cortical synchronization, in both electrophysiological (by EEG) and hemodynamic (by fNIRS) components, could emerge between two brains during cooperation. Also, we intended to explore arousal-related peripheral responses during the task. To explore these issues, 14 participants paired as 7 dyads were recorded with dual-EEG and dual-fNIRS setups while they were engaged in an attentive task finalized to engage cooperation. After a resting period which served as control condition, the task was sub-divided in 8 blocks with a pause halfway assessing the goodness of the cooperation scores. Thus, inter-brain activity coherence over the prefrontal regions was calculated between the two participants across blocks. We found that the coherence between the two signals varied across blocks in accordance to the perceived degree of cooperation. Such differences point toward a modulation between the two subjects’ brain activity as a function of the task, with respect to control conditions. This work represents the first use of dual-EEG/dual-fNIRS setups for simultaneous measurements of brain-to-brain coupling and endorses the use of hyperscanning techniques for social interactive studies in naturalistic environments.