Decaying of Phase Synchronization - A Physiological Tool
  We describe the effects of the asymmetry of cycles and non-stationarity in time series on the phase synchronization method. We develop a modified method that overcomes these effects and apply this method to study parkinsonian tremor. Our results indicate that there is synchronization between two different hands and provide information about the time delay separating their dynamics. These findings suggest that this method may be useful for detecting and quantifying weak synchronization between two non-stationary signals. 
Avi Gozolchiani, Shay Moshel, Jeffrey M. Hausdorff, Ely Simon, Jurgen   Kurths, Shlomo Havlin