Fig. 1

Tracings showing progression from full wakefulness to deep sleep. Both tracings a and b were staged awake despite their substantially different visual appearance and the presence of a 12-second period of sleep in b (horizontal line; 15 s of sleep are required to score sleep). Although its pattern is substantially similar to that of tracing b, tracing c was scored asleep (stage 1) because the sleep pattern lasted 18 s (horizontal line). Tracings d and e were both scored stage 2 even though the pattern in d is very similar to stage 1 (c), but a spindle appeared, while the pattern in e is very similar to delta sleep (f) but the duration of delta waves was just shy of 6 s. The numbers within each tracing are the 3-second odds-ratio-product (ORP) values and the number to the right of each tracing is the 30-second ORP average. Note the marked difference in ORP distribution within the two awake tracings and the transient reduction in ORP during the brief sleep in tracing b. ORP values are quite different between the two stage 2 epochs with ORP in tracing d being close to that in tracing c while ORP in tracing e being similar to that of tracing f. C3/A2, electroencephalogram. ORP reflects the visual appearance of the EEG. Adapted from (Younes et al. 2015a)