Figure 1.

Single-Hz electroencephalographic (EEG) topography (left side, frequency range = 0.50–11 Hz; right side, frequency range = 12–24 Hz) at sleep onset (SO) after a period of prolonged wakefulness. In both halves of the figure, the first two columns show the topographic distribution of absolute EEG power in the 5-min intervals before SO and after SO, respectively. The maps were scaled between minimal (min) and maximal (max) values calculated for all frequencies and derivations in before SO and after SO periods. The third column shows the relative EEG changes expressed as the ratio between after SO and before SO periods. The maps were scaled between min and max values in before SO and after SO periods. The fourth column depicts the topographical statistical EEG power differences (assessed by paired t-tests) between these 5-min periods. Values are expressed in t-values: positive t-values indicate a prevalence of the after SO period and vice versa. The two-tailed level of significance is indicated by the arrow in correspondence of the t-values color bar (p ≤ 0.0005 corresponding to t ≥ 3.79 after the Bonferroni correction). White dots indicate significant differences after the Bonferroni corrections. Values are color-coded and plotted at the corresponding position on the planar projection of the scalp surface and are interpolated (biharmonic spline) between electrodes. The maps are based on the 19 unipolar EEG derivations of the international 10–20 system with averaged mastoid reference, and they are plotted for each frequency Hz bin in the 0.50- to the 24.75-Hz range.