Quantitative Sleep Monitoring - Quantitative EEG Analysis Methods and Clinical Applications - page 263

Awake with eyes closed
(a)
Awake with eyes open
(b)
Figure 10.3 Typical patterns of eye movements. (a) SEMs are pendular and are common in drowsy
wake and stage 1 sleep. (b) REMs are sharper (shorter duration) and are seen in eyes-open wake or
REM sleep. (Courtesy of James Geyer and Paul Carney.)
essential element only for identifying stage REM sleep. In stage REM, the chin EMG
is relatively reduced—the amplitude is equal to or lower than the lowest EMG
amplitude in NREM sleep. If the chin EMG gain is adjusted high enough to show
some activity in NREM sleep, a drop in activity is often seen on transition to REM
sleep. The chin EMG may also reach the REM level long before the onset of REM
sleep or an EEG-meeting criteria for stage REM. Depending on the gain, a reduction
in the chin EMG amplitude from wakefulness to sleep and often a further reduction
on transition from stage 1 to 4 may be seen. However, a reduction in the chin EMG
is not required for stages 2 to 4. The reduction in the EMG amplitude during REM
sleep is a reflection of the generalized skeletal-muscle hypotonia present in this sleep
stage. Phasic brief EMG bursts still may be seen during REM sleep. In Figure 10.4,
there is a fall in chin EMG amplitude just before the REMs occur. The combination
of REMs, a relatively reduced chin EMG, and a low-voltage mixed-frequency EEG
is consistent with stage REM.