Sleep spindles: Decomposition, parameterization and applications

A new methodology for sleep spindles characterization based on the amplitude/frequency modulation (AM/FM) model is introduced after an empirical mode decomposition (EMD) signal procedure. A set of intrinsic mode functions (IMF) is obtained which are basically AM/FM signals that we can demodulate to obtain sets of parameters characterizing the amplitudes and phases. The demodulation leads to the instantaneous envelope (IE) and the instantaneous frequency (IF) estimation and subsequent modelling as AM/FM signals. Three AM/FM models are compared for the analysis of the signals under scrutiny. For the calculation of the model parameters two different methods were also used, namely, the least squares method and genetic algorithms. Finally, the parameters of the AM/FM model are used to compare healthy and Alzheimer or dementia patients. It was concluded that, based only on analysis of the IMF in the range of 11-15 Hz, five parameters of the model can quantify significantly changes on the structure of sleep spindles in patients with dementia. In (Ktonas, 2007) it was carried out a similar study, but based on “complete” sleep spindles and, for the same AM/FM model, only two of the parameters showed significant variations. This led us to believe that the IMFs, not only can quantify the variations in the structure of sleep spindles of demented patients, as they do it in a more expressive form.