Cover picture: The general pattern of origin and propagation of sleep slow oscillations (<1 Hz) obtained from high-density EEG recordings during one night. Each column is a separate subject. The first row contains the detection density maps. The probability of each electrode detecting the slow oscillation was highest over the frontal lobe. The second row contains the origin density maps. Note that the clusters of electrodes with the highest origin density were located on the most anterior scalp regions, overlying the orbitofrontal cortex. The third row contains the average delay maps. The prevalent direction of propagation was anteroposterior. Note that on average, channels located at homotopic scalp sites tended to have a similar delay. For details, see Figure 7 from the article by Massimini et al. in this issue (pages 6862–6870).