The two-brain approach: how can mutually interacting brains teach us something about social interaction?

Abstract

Measuring brain activity simultaneously from two people interacting is intuitively appealing if one is interested in putative neural markers of social interaction. However, given the complex nature of interactions, it has proven difficult to carry out two-person brain imaging experiments in a methodologically feasible and conceptually relevant way. Only a small number of recent studies have put this into practice, using fMRI, EEG, or NIRS. Here, we review two main two-brain methodological approaches, each with two conceptual strategies. The first group has employed two-brain fMRI recordings, studying (1) turn-based interactions on the order of seconds, or (2) pseudo-interactive scenarios, where only one person is scanned at a time, investigating the flow of information between brains. The second group of studies has recorded dual EEG/NIRS from two people interacting, in (1) face-to-face turn-based interactions, investigating functional connectivity between theory-of-mind regions of interacting partners, or in (2) continuous mutual interactions on millisecond timescales, to measure coupling between the activity in one person's brain and the activity in the other's brain. We discuss the questions these approaches have addressed, and consider scenarios when simultaneous two-brain recordings are needed. Furthermore, we suggest that (1) quantification of inter-personal neural effects via measures of emergence, and (2) multivariate decoding models that generalize source-specific features of interaction, may provide novel tools to study brains in interaction. This may allow for a better understanding of social cognition as both representation and participation.

Frontal alpha oscillations distinguish leaders from followers: Multivariate decoding of mutually interacting brains

“…Given the methodological and conceptual challenges of studying brain mechanisms of social interaction, hyperscanning still has a long way to go, and explorative analyses can be useful in decoding both synchronized and complementary mechanisms in two-brain data during more natural interactions (Konvalinka and Roepstorff, 2012). While our original hypothesis was not regarding differences in brain signals between leaders and followers, this distinction was uncovered given our data-driven approach.…”

Rhythm in joint action: psychological and neurophysiological mechanisms for real-time interpersonal coordination

“…This phenomenon has been observed in dual-EEG studies employing diverse tasks requiring joint rhythmic behaviour, such as guitar duet performance [75][76][77], unconscious imitation of finger movements [78], explicit imitation of hand movements [79] and joint speech [80]. Dual-EEG set-ups provide a promising avenue for exploring the temporal dynamics of mechanisms supporting rhythmic joint action, though the complexity of such set-ups means that caution must be exercised to ensure that studies are conceptually and methodologically sound [81,82].…”

Near-Infrared Spectroscopy Applied to Complex Systems and Human Hyperscanning Networking

“…Even if these implications are still mainly theoretically discussed, those modulations could be measured via dynamical systems techniques [14] or quantified by looking at long-term correlations [56]. Again, machine-learning methods might be useful to mine neural data and identify relevant markers of sustained/broken coordination [57].…”