When people in a group are more engaged with each other and with the world around them, their brainwaves show remarkably similar patterns. That's the conclusion of researchers who used portable EEG to simultaneously record brain activity from an entire class of high school students over the course of a full semester as they went about their regular classroom activities. The findings reported in Current Biology on April 27 highlight the promise of investigating the neuroscience of group interactions in real-world settings.

"We found that students' brainwaves were more in sync with each other when they were more engaged during class," says co-lead author Suzanne Dikker of New York University and Utrecht University. "Brain-to-brain synchrony also reflected how much students liked the teacher and how much they liked each other. Brain synchrony was also affected by face-to-face social interaction and students' personalities. We think that all these effects can be explained by shared attention mechanisms during dynamic group interactions."

The researchers, led by David Poeppel of New York University and the Max Planck Institute of Empirical Aesthetics, used portable EEG to simultaneously record the students' brain activity. Researchers Lu Wan and Mingzhou Ding of the University of Florida then used novel analyses to assess the extent to which that brain activity was synchronized across students and how the degree of synchrony varied with class engagement and social dynamics.

The researchers think that the level of synchrony comes from a well-known phenomenon called neural entrainment. "Your brainwaves 'ride' on top of the sound waves or light patterns in the outside world, and the more you pay attention to these temporal patterns, the more your brain locks to those patterns," Dikker explains. "So, if you and the person next to you are more engaged, your brainwaves will be more similar because they are locking onto the same information."

Brain synchrony most likely supports synchronized behavior during human interaction. For example, synchrony is required for two or more people to have a good conversation, walk down the street, or dance, or carry a heavy piece of furniture. The findings suggest that social dynamics matter, even when people are just listening to the same lecture or watching the same video.

The researchers are now designing large-scale projects in which they'll be able to record brain data and other biometrics from up to 45 people simultaneously in an auditorium. They hope to answer questions such as, "What are the 'optimal' conditions for an audience to experience a performance or movie? Is there an ideal group size? Does having some joint interaction right before a performance improve the experience? How does the audience affect the performer and vice versa?"