Sleep depth oscillations: an aspect to consider in automatic sleep analysis.

The automatic sleep analysis aims at providing an accurate description of sleep process. We found that there exist so far poorly known sleep depth oscillations constantly. Quantitative analysis of these oscillations was done in this work via a mean frequency measure and FFT. Overall charasteristics of these oscillations were studied, focusing on the waves with period times of 5-150 s. These sleep depth oscillations have a relatively large amplitude and they should be considered in future sleep analysis systems. The results of this study give directions to automated sleep analysis regarding optimal estimation of sleep depth.