Comparison of EEG synchrony measures for post-stroke neurorehabilitation

In post-stroke neurorehabilitation, the Functional Independence Measure (FIM) is a standard clinical scale used to assess patient's activities of daily living. Recently, we reported a new electroencephalography-based biomarker (the phase synchrony index) that correlates with this scale. For a more comprehensive evaluation, we compared three synchrony measures: phase synchrony index, phase lag index, and imaginary part of coherency. These synchrony measures showed a significant correlation with FIM motor subscores in the same frequency bands, but in different ways. These differences may be partly attributed to the susceptibility to the spurious synchrony by volume conduction effects and/or presence of the ceiling effect of synchrony measures. Our results suggest that we should select an appropriate synchrony measure as a biomarker for stroke recovery depending on the brain network of interest.