Fig. 2.

Example showing the HFO rate and the time varying rate predicted by two Poisson process models common for every subject. The prediction in black corresponds to a model taking into account sleep stage and accumulated time in each stage. The prediction of the best model is shown in blue, and includes also the variables measuring the slow wave amplitude, the sigma band activity, and in the case of pathological ripples and fast ripples also the delta band activity. The rate is plotted as a function of time, and the sleep stage is indicated in color at the bottom of the graphs. Observe the rate increase with time during REM sleep for physiological ripples by comparing the vertical position of the red arrows, and a decrease during NREM sleep for pathologic ripples and fast ripples (most marked during stage N3, indicated also by the difference in the vertical position of the arrows). Note that the rate of physiological ripples is always below 15 per hour across the whole night's NREM sleep, and the rate of pathological HFOs is above 20 per hour during NREM sleep, but there is a larger difference in physiological and pathological HFO rates during the first sleep cycle as compared to the last sleep cycle.