Synchrony in social interaction

Humans are social animals. What does it mean to be social? A great many things, I am sure, would be put forward to answer that question and most would be accurate. I am intrigued by how we manage to coordinate: coordinate to communicate, coordinate in joint actions, coordinate to align goals. I cannot imagine social life without coordination between people.

Recently there was a report in the Scientific American on work by Uri Hasson. He showed a coupling between brain activity in a speaker and listener but only when there was verbal understanding. This work used fMRI, so it was difficult to arrange a real conversation against the noise and isolation of the equipment. We seems to be able to steer one another’s brain activity. Previous blog is communication between brains.

Now, in PloS is a different take on how brains coordinating, a paper by Dumas, Nagel, Soussignan, Martinerie and Garners, Inter-Brain Synchronization during Social Interaction (here). In this case the behaviour that was being aligned was meaningless hand movements. Subjects could create their own movements, mimic each other or not, synchronize their movements or not, and control taking turns while their EEGs and behaviour were recorded. Here is the abstract:

During social interaction, both participants are continuously active, each modifying their own actions in response to the continuously changing actions of the partner. This continuous mutual adaptation results in interactional synchrony to which both members contribute. Freely exchanging the role of imitator and model is a well-framed example of interactional synchrony resulting from a mutual behavioral negotiation. How the participants’ brain activity underlies this process is currently a question that hyperscanning recordings allow us to explore. In particular, it remains largely unknown to what extent oscillatory synchronization could emerge between two brains during social interaction. To explore this issue, 18 participants paired as 9 dyads were recorded with dual-video and dual-EEG setups while they were engaged in spontaneous imitation of hand movements. We measured interactional synchrony and the turn-taking between model and imitator. We discovered by the use of nonlinear techniques that states of interactional synchrony correlate with the emergence of an interbrain synchronizing network in the alpha-mu band between the right centroparietal regions. These regions have been suggested to play a pivotal role in social interaction. Here, they acted symmetrically as key functional hubs in the interindividual brainweb. Additionally, neural synchronization became asymmetrical in the higher frequency bands possibly reflecting a top-down modulation of the roles of model and imitator in the ongoing interaction.

It is fairly clear that synchronized activity in the brain is important to the nature of thought. Different rhythms are involved in different activities. Hebb’s famous quote, “cells that fire together, wire together”could also be, “cells that fire together, give us consciousness”. Or it could be enlarged in scope to “brains that fire together, communicate.”

we were able to show that the alpha-mu rhythm was the most robust interbrain oscillatory activity discriminating behavioral synchrony vs. non synchrony in the centroparietal regions of the two interacting partners. The alpha-mu band is considered as a neural correlate of the mirror neuron system functioning. Specific frequencies of this band (9.2–11.5 Hz) over the right centroparietal region have been proposed as a neuromarker of social coordination.

This work and, I hope, future research along these lines are very important steps towards understanding our social nature.

Citation: Dumas G, Nadel J, Soussignan R, Martinerie J, Garnero L (2010) Inter-Brain Synchronization during Social Interaction. PLoS ONE 5(8): e12166. doi:10.1371/journal.pone.0012166

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