Transition from NREM 2 to REM sleep

Two 30-second epochs of sleep recorded in a 14-year-old during overnight PSG. The second epoch (labeled 768) is easily scored as REM sleep, because it contains all of the typical PSG features of REM sleep (rapid eye movements, low voltage mixed frequency EEG, and chin muscle atonia). Scoring of the first epoch (labeled 767) is more complex. In the epoch before (not shown), chin muscle tone was preserved, sleep spindles were seen, and it was scored as NREM 2. In epoch 767, a 3-second arousal is seen (diffuse 14 Hz activity), and there are no sleep spindles. Beginning 3 seconds into epoch 767, the chin EMG increases after the arousal, then drops to its lowest amplitude in the sleep study. Epoch 767 is therefore best scored as NREM 1 sleep, and epoch 768 as REM sleep. An arousal such as this one often occurs in the transition from NREM 2 to REM sleep.