Hyperscanning

Hyperscanning records two or more brains simultaneously while the people interact — talking, cooperating, playing a game — using synchronized EEG, fNIRS, fMRI, or MEG. Introduced by Montague and colleagues (2002), it is a read-only method for studying the neural basis of social interaction, and it is emphatically not a brain-to-brain link: no signal is written into any participant, and the brains are coupled only through the ordinary social channel of the shared task and environment.

Its main measure is inter-brain synchrony or coupling — statistical dependence between the two brains' activity — which is reported to rise with cooperation, joint attention, teaching, and rapport. The inferential pitfalls are serious: shared sensory input, common motor rhythms, and correlated artifacts can all manufacture apparent synchrony, so credible studies use control pairs (people recorded at the same time but not interacting) and surrogate statistics to rule out spurious coupling.