Multiple trial processing of multivariate phase synchronization in brain signals

The quantification of phase synchrony is important for the study of large-scale interactions in the brain. Current methods for computing phase synchrony are limited to the estimation of the stability of the phase difference between pairs of signals over a time window, within successive frequency bands. These approaches cannot quantify the synchrony across a group of electrodes and over time-varying frequency regions from multiple trials. In this paper, we address this issue by quantifying the frequency locking between groups of electrodes using a time-frequency based estimation of the instantaneous frequency. The instantaneous frequency maps of individual electrodes are combined to obtain the instantaneous frequency histogram as an estimate of the amount of frequency locking across electrodes. This analysis is then extended to the estimation of frequency locking across multiple electrodes and trials. Results are shown for both synthetic signal models and electroencephalogram (EEG) data collected from control and schizophrenic subjects.