Intra and inter-brain connectivity during cooperation: a fNIRS-based connectivity analysis

Research suggested that during social interactions typical forms of synchronization in two individuals’ brains can occur in the form of an alignment of neural activity (brain-tobrain coupling). To explore these issues hyperscanning paradigms emerged thus permitting the simultaneous recording of the cortical activity from two or more participants interacting together. Nonetheless, new neurophysiological techniques are required to monitor these processes to allow flexible and ecological settings, such as functional Near-Infrared Spectroscopy, which is portable and constraint-free to acquire data during the interactional setting. In the present study intra and inter-brain connectivity was during a social interaction proposed as an attentive joint task including a feedback, experimentally manipulated. Halfway, in fact, a feedback was provided to participants assessing the goodness of behavioral synchronicity scores. The aim was to compare subjective and inter-subjective brain contribution in the joint-action with respect to the social reinforced cooperation and perception of a good joint-action. Partial correlation coefficients were used as a functional connectivity index for computing both intra and inter-brain coherence, by quantifying the relationship between the different signals. For what concerns intra-brain coherence, results showed a significant difference (p < 0.05) between the first and the second half of the task in the connectivity of channel F2-F4, corresponding to Premotor Cortex (PMC), and F2-FC2, corresponding to Frontal Eye Field (FEF). The link between these two areas account for the subjective efforts during the first part of the task to accompany the detection of visual stimuli with synchronized motor responses. A similar result was found for inter-brain coherence, with higher connectivity between two premotor areas (FC4-FC2 and F2-FC2; p < 0.05) before the social feedback, related to motor planning and imaginary. Finally, higher inter-brain coherence emerged after the social manipulation for FC3-F3 and FC4-F4 (p < 0.05), which correspond to left and right Dorsolateral Prefrontal Cortex (DLPFC). With respect to previous brain networks, this area has been proved to be involved in social cognition. Thus, the presence of enhanced emotional and social processes related to empathy and bonding could be hypothesized after the feedback. The present results provided new insights in the identification of brain areas with specific functional roles in intra and inter-brain coherence during interpersonal coordination. Importantly, the social feedback permitted to distinguish brain networks specifically related to motor synchronization and emotional/social tuning.