Neuroimaging researchers typically consider the brain's response as the mean activity across repeated experimental trials and disregard signal variability over time as "noise". However, it is becoming clear that there is signal in that noise. This article describes the novel method of multiscale entropy for quantifying brain signal variability in the time domain.
Heisz, J. J., McIntosh, A. R. Applications of EEG Neuroimaging Data: Event-related Potentials, Spectral Power, and Multiscale Entropy. J. Vis. Exp. (76), e50131, doi:10.3791/50131 (2013).