All of the following statements are true about the changes seen from stage N2 to N3 EXCEPT:

• A. Sleep spindles may persist into stage N3 sleep
• B. Delta activity reaches 20% or more in the epoch
• C. EMG chin activity is often higher than in stage N2
• D. Eye movements are not typically seen

Answer: (C)

From N2 to N3 the EEG shifts to slower, higher-amplitude activity as sleep deepens. The defining feature of N3 is delta activity that makes up 20% or more of the epoch. Sleep spindles are typical of N2, but they can persist into early N3 at the transition, though they tend to diminish as delta dominates. Eye movements disappear in non-REM sleep, so no rapid eye movements are expected in N3. Muscle tone also lowers in deep sleep, so chin EMG activity is reduced compared with N2, not higher. The statement about chin EMG being higher in N3 contradicts this pattern, making it the exception.