Temporal coherence of superimposed EEG waves: a problem in nonlinearity

Traditional "stimulus-time-locked signal averaging" of human EEG, as usually practiced in both clinical and basic contexts, assumes the superposition principle of algebraic summation for a linear time series. But there are now experimental data on nonlinear coupling of neural populations in the brains of two species, and reasons for regarding human EEG as a nonlinear, chaotic time series, reflecting a global mixture of subharmonics and harmonics of continually varying "fundamental" frequencies within the commonly observed power spectrum of a subject attending to sensory input (about 3-35 Hz). So we must ask ourselves if the established conventions for averaging and temporal comparison of both scalp-conducted voltages and related magnetic fluxes from human heads are appropriate for the suspected nonlinear coupling of neural oscillators.