Coordination of brain waves between humans facing territorial threats.

Here is an interesting piece from Mu et al., first their abstract, and then a chunk of their introduction which gives rationale and background.

Abstract

Throughout history and into the modern era, human groups have been continually subjected to a wide range of societal threats, from natural disasters to pandemics to terrorism. Yet despite this fundamental aspect of human existence, there has been little research on how societal threat affects social coordination at both the neural and the behavioral level. Here, we show for the first time that individuals are better able to coordinate under high societal threat as compared to low or no threat (Experiment 1). Using a method of hyperscanning electroencephalography (EEG), which simultaneously measures brain activity among interacting subjects, we further illustrate that interbrain synchrony of gamma band oscillations is enhanced when people are under high threat, and increased gamma interbrain synchrony is associated with lower dyadic interpersonal time lag (i.e. higher coordination) (Experiment 2). To our knowledge, the current work provides some of the first empirical evidence that gamma interbrain synchrony is associated with social coordination when humans are under threat.

And, excerpts from their introduction:

...there has been little research on the behavioral or neural mechanisms through which humans coordinate under high societal threat. From an evolutionary point of view, the ability of humans to effectively synchronize their actions under threat would presumably confer an important survival advantage.

To address this question, we combine state of the art hyperscanning techniques with exposure to real-world threat. Hyperscanning techniques, which record multiple brains’ neural activity simultaneously with great precision as humans interact over time, are perfectly situated to elucidate the interbrain mechanisms underlying social coordination under high societal threat. Accumulating hyperscanning eletroenthephalograph (EEG) studies have indeed shown that interbrain synchrony plays a critical role in various forms of human coordination, such as the ability to synchronize body movements and speech rhythms and to perform duets.

We complement previous research by examining the role interbrain synchrony plays in coordination when humans are under threat. Using a coordination game validated in previous research (Mu et al., 2016), in Experiment 1, we examined whether dyads exposed to ingroup threat (IGT) would exhibit greater coordination as compared to dyads exposed to outgroup threat (OGT) or no threat control conditions (IGC).

In Experiment 2, we combined hyperscanning EEG with the same threat manipulation (i.e. IGT, OGT and IGC) and the same coordination game employed in Experiment 1 to investigate whether interbrain synchrony would help humans coordinate under conditions of high societal threat. Using a dual-EEG setup, we tested how societal threat influences interbrain synchrony while participants attempted to coordinate. Previous hyperscanning EEG studies have shown that alpha interbrain synchrony is activated in a variety of social coordination tasks, including interactional synchrony, coordinated teamwork and synchronized counting. Thus, we examined whether alpha interbrain synchrony would be recruited to support social coordination in an unexplored context, namely that of societal threat.

We also examined other bands of interbrain synchrony which may be particularly relevant to social coordination under threat—most notably gamma band, a high frequency band (>28 Hz) that is a threat-sensitive neural marker. In particular, single brain analyses have shown that gamma band oscillations contribute to threat detection, reflecting the involvement of a quick subcortical route to the amygdala, which plays a central role in processing threat-related stimuli, such as fearful images and threat-related words. Gamma activity is also higher in anxiety disorder patients who experience chronic fear. Thus, if threat affects interpersonal coordination by modulating interbrain synchrony linked to threat processing, we would expect that gamma band synchrony may be associated with human coordination under threat.

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