Brain-to-brain synchrony predicts long-term memory retention more accurately than individual brain measures

Little is known about the brain mechanisms that underpin how humans learn while interacting with one another in ecologically-valid environments (-). This is because cognitive neuroscientists typically measure one participant at a time in a highly constrained environment (e.g., inside a brain scanner). In the past few years, researchers have begun comparing brain responses across individuals (-) demonstrating that brain-to-brain synchrony can predict subsequent memory retention (-). Yet previous research has been constrained to non-interacting individuals. Surprisingly, the one study that was conducted in a group setting found that brain synchrony between students in a classroom predicted how engaged the students were, but not how much information they retained (). This is unexpected because brain-to-brain synchrony is hypothesized to be driven, at least partially, by shared attention (, ), and shared attention has been shown to affect subsequent memory (). Here we used EEG to simultaneously record brain activity from groups of four students and a teacher in a simulated classroom to investigate whether brain-to-brain synchrony, both between students and between the students and the teacher, can predict learning outcomes (). We found that brain-to-brain synchrony in the Alpha band (8-12Hz) predicted students’ delayed memory retention. Further, moment-to-moment variation in alpha-band brain-to-brain synchrony discriminated between content that was retained or forgotten. Whereas student-to-student brain synchrony best predicted delayed memory retention at a zero time lag, student-to-teacher brain synchrony best predicted memory retention when adjusting for a ∼200 millisecond lag in the students’ brain activity relative to the teacher’s brain activity. These findings provide key new evidence for the importance of brain data collected simultaneously from groups of individuals in ecologically-valid settings.