Synchronization of Brain Waves While Speaking and Listening

Written by Brett Weiss

February 2019

Perez et al. (2016) report synchronization of brain waves during speaking and listening i.e. a situation similar to speaking on the phone.  The researchers measured brain waves with electroencephalography, a method which uses electrodes on the scalp to monitor brain wave activity.  The process of brain wave synchronization between individuals conversing is called ‘entrainment.’

The group mentioned that entrainment may occur due to the speech signal or due to the social interaction (verbal communication itself).  The group hypothesized that brain-to-brain entrainment occurs due to social interaction through speech (not just due to speech signal). 

Perez et al. (2016) found that brain-to-speech synchronization occurred at lower frequencies of delta and theta.  The group got rid of data from electrodes where brain-to-brain synchronization is explained by entrainment to speech.  They found that higher-frequency brain waves remained which were alpha and beta waves.  For alpha waves, interbrain coupling occurred mostly in frontal cortex for listener and central cortex for speaker.  In the beta band, interbrain coupling occurred in the frontal cortex mainly for speaker and the temporal cortex for listener.  Alpha frequencies have been associated with attentional processes, and beta frequencies have been associated with language comprehension and motor function.

The authors went on to say that alpha and beta frequencies could constitute rhythmic categories involved in top-down processing (top-down processing initiates thoughts).  Thus, they say that brain-to-brain entrainment in alpha and beta frequencies could be part of an emergent property (what a complex system has that parts alone do not have) of coupled systems.  Coupled systems, in this case two individuals having a conversation, may have this emergent property due to prediction processes from the interaction.  This phenomenon may facilitate effective social coordination (Perez et al., 2016).

In essence, the observation of alpha and beta frequency brain-to-brain synchronizations that do not occur due to speech entrainment remains a mystery.  Could this observation constitute an emergent property of a ‘hyper-brain’ of sorts forming when two individuals communicate?  How could scientists prove or discredit (falsify) the notion of a hyper-brain forming between two individuals in verbal communication?  Are there other mechanisms that might explain the emergent property of brain-to-brain synchronizations that do not occur due to speech entrainment?


  1.  Perez A, Carreiras M, Dunabeitia JA (2016).  “Brain-to-brain entrained: EEG interbrain synchronization while speaking and listening.”  Sci Rep.  7(1): 1-12.
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