
FIGURE 4.12: Time frequency maps of EEG signal energy for 20-second epochs
from different sleep stages shown above the corresponding signals. a) Wakefulness,
alpha waves marked by arrows; b) stage 2, two spindles and K-complex marked; c)
stage 3, two slow waves and a K-complex marked; d) stage 4, slow waves marked.
From [Malinowska et al., 2006].