Frequencies in frontal an parietal derivations

Figure 2 is composed from histograms of frequencies of sleep spindles plotted for each channel and placed on page according to relative position of electrodes (table 2). We notice that higher frequencies are present in posterior, and lower--in anterior derivations. This trend, present in all the analyzed recordings, conforms to the hypothesis of two generators of sleep spindles [Jankel and Niedermayer, 1985] [Jobert et al., 1992].

Figure: Histograms of frequencies of sleep spindles detected in one overnight EEG recording. Plots are placed on page according to relative positions of corresponding derivations (Table 2 on page )--front of head towards the top of page. We observe sparse occurences in peripheral (Fp*, O*, T* and F[7-8]) electrodes, therefore in the following multi-derivations plots (figures 3, 8, 9) results only for the central 9 derivations (O*, C* and F[3,4,z]) will be presented.

Figure 3: Amplitudes of detected spindles (vertical) plotted versus their frequencies (horizontal) for the nine central derivations from Figure 2.

In Figure 3 each spindle is marked in the frequency (horizontal) vs. amplitude (vertical) coordinates. Plots for each channel are positioned as in the previous figure. We observe that for predominant frequencies spindles of higher amplitudes are present.