Figure 9.

Upper airway muscle activity during REM sleep in subjects with fully patent upper airway is dominated by nonrespiratory, phasic bursts that emerge from an otherwise atonic state. (A) Activity of the arytenoid (laryngeal) muscle during REM sleep in a healthy human subject. (Fig. 9 in Ref. 278 republished with permission from the American Physiological Society.) (B) Average time course of lingual muscle activity during transitions from NREM to REM sleep in rats. Lingual and nuchal EMG levels were measured during successive 10 s intervals from 60 s before to 200 s after the state transition (time zero) and averaged over multiple transitions in multiple animals. Root mean squares of muscle activity were normalized within each animal by their average levels during wakefulness. The bottom graph shows the corresponding average time course of the ratio of EEG powers in β-2 to Δ-2 bands (the ratio characteristically increases during REM sleep). Lingual and nuchal EMGs follow a different time course during the transition. Whereas nuchal EMG declines prior to the onset of REM sleep and then maintains a low level (atonia), lingual EMG is nearly atonic prior to the onset of REM sleep (see Fig. 8B) and first gradually increases and then declines after REM sleep onset. The relatively smooth time course of the increase and then decline is a result of averaging of many short bursts of activity (twitches) across many NREM to REM sleep transitions. The resulting mean time course indicates that, after the onset of REM sleep, individual twitches first become gradually larger and more frequent and then gradually become smaller and less frequent when the duration of REM sleep episodes extends beyond its mean (90 s in rats). (Modified from Fig. 6 in Ref. 446 and republished with permission from Archives Italiennes de Biologie and the University of Pisa.)