On the amplitude modulation in the various frequency bands of sleep EEG

The slow amplitude modulation of each conventional frequency band of the EEG signal, recorded during sleep in normal subjects, is examined. The delta band exhibits an approximate proportionality between band activity and modulation amplitude, that is an approximately constant percentage of modulation that has been found. On the contrary, the sigma band modulation is characterized by a peculiar pattern. The properties of the delta band are shared with the other EEG bands. The purpose of this paper is to provide a general description of both the peculiarity of the sigma band and the similarity among the other bands.