A study of automatically computed parameters related to sleep microstructure

A simple method for the quantitative description of sleep microstructure is proposed. The application of this method makes it possible to recognize epochs characterized by the increase in the amplitude of some band activity. The length of these epochs and the time distance between two successive epochs are measured. The method is based on the consideration that the values of the band activity amplitudes, when averaged over time intervals in the order of approximately 1 minute, are generally related to the macrostructure, but, when averaged over shorter time intervals, tend to concern both the macrostructure and microstructure. From the calculation of these two different kinds of averages, it is possible to derive an adimensional descriptor closely related to the microstructure. The method was applied examining 4 frequency bands (1 to 4 Hz, 4 to 8 Hz, 8 to 12 Hz and 12.5 to 14.5 Hz), choosing the shorter time interval equal to 2 s and the longer equal to 64 s, and putting the threshold for the descriptors equal to 1. The results obtained automatically with this method were in close agreement with those provided by visual analysis.