Studies of the coefficient of variation of the magnitude of EEG signals

An analysis of the variation in magnitude of EEG signals in various frequency bands of anesthetized patients and normal sleeping volunteers was carried out. The coefficient of variation (CoV), i.e. the standard deviation/mean, within 10 second epochs was found to be quite constant throughout the whole of the EEG recordings and was typically about 0.46. This was found to be the case for both the patients and the volunteers. Histograms of the magnitudes indicated that the magnitudes are distributed as f(x)=/spl beta/xe(-/spl alpha/x/sup 2/) functions. However a CoV of 0.46 is consistent with f(x)=/spl beta/xe(-/spl alpha/x/sup 3/) functions. The non-stationary nature of the EEG is such that it is likely that while over short periods the EEG magnitudes are distributed as f(x)=/spl beta/xe(-/spl alpha/x/sup 3/) functions, variations of /spl alpha/ over time mean that in the long term the EEG magnitudes are distributed as f(x)=/spl beta/xe(-/spl alpha/x/sup 2/) functions.