  The fluctuation properties of the human electroencephalogram (EEG) time
series are studied using detrended fluctuation analysis. For all 128 channels
in each of 18 subjects studied, it is found that the standard deviation of the
fluctuations exhibits scaling behaviors in two regions. Topographical plots of
the scaling exponents reveal the spatial structure of the nonlinear electrical
activities recorded on the scalp. Moment analyses are performed to extract the
gross features of all the scaling exponents. The correlation between the two
scaling exponents in each channel is also examined. It is found that two
indices can characterize the overall properties of the fluctuation behaviors of
the brain dynamics for every subject and that they vary widely across the
subjects.
