Spherical harmonic decomposition applied to spatial-temporal analysis of   human high-density EEG
  We demonstrate an application of spherical harmonic decomposition to analysis of the human electroencephalogram (EEG). We implement two methods and discuss issues specific to analysis of hemispherical, irregularly sampled data. Performance of the methods and spatial sampling requirements are quantified using simulated data. The analysis is applied to experimental EEG data, confirming earlier reports of an approximate frequency-wavenumber relationship in some bands. 
Brett M. Wingeier, Paul L. Nunez, Richard B. Silberstein