On the Existence of Synchrostates in Multichannel EEG Signals during Face-perception Tasks
This research addresses the need for better temporal resolution in EEG phase synchronization analysis, potentially offering new insights into brain connectivity for cognitive and clinical applications, though it appears incremental by bridging existing concepts of EEG microstates and phase synchronization.
The study tackled the problem of analyzing phase synchronization in multichannel EEG signals by proposing a method to identify unique, stable phase-synchronized patterns called 'synchrostates' during face-perception tasks, observing their consistent existence across 44 subjects in beta and gamma frequency bands with topographies varying by pathological conditions.
Phase synchronisation in multichannel EEG is known as the manifestation of functional brain connectivity. Traditional phase synchronisation studies are mostly based on time average synchrony measures hence do not preserve the temporal evolution of the phase difference. Here we propose a new method to show the existence of a small set of unique phase synchronised patterns or "states" in multi-channel EEG recordings, each "state" being stable of the order of ms, from typical and pathological subjects during face perception tasks. The proposed methodology bridges the concepts of EEG microstates and phase synchronisation in time and frequency domain respectively. The analysis is reported for four groups of children including typical, Autism Spectrum Disorder (ASD), low and high anxiety subjects - a total of 44 subjects. In all cases, we observe consistent existence of these states - termed as synchrostates - within specific cognition related frequency bands (beta and gamma bands), though the topographies of these synchrostates differ for different subject groups with different pathological conditions. The inter-synchrostate switching follows a well-defined sequence capturing the underlying inter-electrode phase relation dynamics in stimulus- and person-centric manner. Our study is motivated from the well-known EEG microstate exhibiting stable potential maps over the scalp. However, here we report a similar observation of quasi-stable phase synchronised states in multichannel EEG. The existence of the synchrostates coupled with their unique switching sequence characteristics could be considered as a potentially new field over contemporary EEG phase synchronisation studies.